Socio-economic issues related to stock enhancement in inland waters

		Produced by:  Regional Office for Asia and the Pacific
	Title:  A review of stock enhancement practices in the inland water fisheries of Asia...	PDF version

It is evident from the preceding sections that all forms of stock enhancement in the Asian region have one purpose: to increase the foodfish supplies, thereby contributing to human nutrition, providing additional employment opportunities, and in the long term, contributing significantly to poverty alleviation. It is also important to note that the great bulk of stock enhancement practices in Asia occur in rural areas, by design rather than choice, because the waterbodies used for this purpose happen to be located in rural areas.
One of the major features of larger waterbodies in Asia is that they are often common-property, open-access resource waters. This could be one reason that stock enhancement in large, lacustrine waters, in most Asian countries, such as lakes and reservoirs, has not yielded the expected results. Floodplain stock enhancements, which are designed to enhance fisheries benefits in a more equitable manner, have been undertaken in Bangladesh and Myanmar. However, it must be recognized that despite the effort to deliver benefits to the fishing community as a whole, social traditions and hierarchies are still prevalent and often an integral part and parcel of the societal structure, thus benefits may not be distributed evenly and may still be captured by an elite group.
As previously discussed, the success of most stock enhancement practices is highly dependent upon community participation. Different practices bring together different communities. Enhancement in beels in Bangladesh succeeds when coherent groups of traditional fishers are formed, whereas culturebased fisheries depend on mobilizing farmer groups into adopting a somewhat alien practice that will generate synergies and community well being for individual and community benefit. In all instances, some intervention is needed, at least at the initial stages, that will finally culminate in sustainable practices managed and owned by the relevant community/stakeholders. The successful stock enhancement practices that are prevalent in the region are perhaps good examples of the purposeful secondary use of a primary resource - water - for the community well being, whose benefits are expected to filter down to other such activities as the practices mature.
Of course there is also a down side to stock enhancement. In the main, this pertains to stock enhancement of large lacustrine waters, which are usually a common-property resource. All evidence indicates, with perhaps the single exception of stocking giant river prawn in Thai reservoirs, that the returns are not cost-effective. Indeed, the most devastating affect on inland fisheries, resulting in a complete collapse of the inland fishery in large lacustrine waters, occurred in Viet Nam when the subsidized stock enhancement programme was withdrawn by the government as a consequence of economic liberalization that commenced in the mid-1980s. Asian countries need to reconsider strategies in respect of stock enhancement of such waters. It may be that the size of fingerlings at enhancement needs to be significantly increased if a economically viable return is to be obtained, or it may be that countries are better advised to use the stocking material for other purposes, such as rationalizing stock enhancement programmes in smaller waterbodies that are more suitable for culture-based fisheries development, and so on. Most importantly, stock enhancement practices should not be used for the sole purpose of political gain, as is often the case.
In contrast to large lacustrine waters, stock enhancement in floodplain and culture-based fisheries has shown to be cost effective, economically viable and sustainable in the long term. It needs to be pointed out however, that the number of socio-economic studies on stock enhancement practices in Asia is few. There is an urgent need for such studies to ensure improvement and sustainability of these practices, and to effect a greater mobilization of the communities. A sizeable array of studies in individual countries will also enable a better comparison of performances among countries and a realization of technologies and extension work that should be put in place in order to achieve better results.
It has also been shown in the previous sections that the success of stock enhancement practices depends largely on the availability of suitable institutional structures, aptly demonstrated for Bangladesh (Toufique 1999), Sri Lanka (Pushpalatha 2001) and Thailand (Lorenzen et al. 1998). In Viet Nam, where culture-based fisheries are in a relatively early stage of development, the average tenure of a lease ranges from three to six years, but varies both between and within provinces. More often than not, farmer lessees find the lease period too short, and the uncertainty has, on occasion, inhibited development. However, with the current commitment of the Government of Viet Nam to develop inland fisheries, it is expected that more uniform lease regulations will be brought forward. Such problems are not unique to Viet Nam. For example, in Sri Lanka the non-perennial, small waterbodies used for culture-based fisheries development are under the purview of the Department of Agrarian Services, which delegates its authority for water management purposes to Farmer Committees that essentially consist of downstream users. However, under the Agrarian Services Act fisheries development/activities are prohibited in such waters, suggesting that there is an urgent need to change the statute to encourage downstream farmers to take up fishery activities. The most important change that is needed in all Asian countries is a change in public perception - that fishery activity in a waterbody does not negatively affect downstream activity and/or use of the waterbody for daily household needs.

---

Biodiversity issues in relation to stock enhancement in inland waters

	Produced by:  Regional Office for Asia and the Pacific
Title:  A review of stock enhancement practices in the inland water fisheries of Asia...

Relatively unregulated tropical rivers and their floodplains support a high biodiversity, rivalling that of the most diverse marine systems. This is due, in part, to extreme ecosystem complexity. Such rivers traditionally support very important, but often under-valued, fisheries (Coates et al. 2003).
Although surface freshwaters account for only a very small proportion of all waters on earth (see Figure 6), they are estimated to contain 2.4 percent of all known living species, and per unit area, are slightly richer in species than is the land (3.0 vs 2.7), and about ten times richer than are the oceans (3.0 vs 0.2) (McAllister 1999). They also account for a relatively richer ichthyofauna, an estimated 41 percent of the approximately 25 000 species of fish occurring in freshwaters. On the negative side, 20 to 35 percent of freshwater fish species are thought to be either threatened or extinct, and 43 percent of crocodilians and 59 percent of freshwater mammals are threatened (McAllister 1999). An analysis of fishes under threat in the 1996 International Union for the Conservation of Nature (IUCN) Red List indicated that species that depend on freshwater at any stage of their lifecycle are 10 times more likely to be threatened than marine and brackishwater species (Froese and Torres 1999). These authors, who confined themselves to only those species listed in FishBase (Froese and Pauley 2005), observed that 547 of the 637 threatened species (nearly 85 percent) had a link to freshwater. All these facts show the need to consider the impacts of stock enhancement on biodiversity if fisheries in inland waters in developing countries are to be sustainable.
There seems to be a common perception that, apart from recent developments such as dam building and a general deterioration of the quality of natural waters, the deliberate and/or accidental introduction of species has had a significant affect on biodiversity. However, De Silva et al. (2004), in reference to tilapias, which have had a major impact on fisheries and aquaculture in the Asia-Pacific region, concluded that there is no objective evidence to show that these introductions have significantly affected biodiversity in the region. Indeed, these authors went on to demonstrate that most of the evidence that has been brought forth previously has been misinterpreted and misconstrued.
Most stock enhancement practices in Asia, except perhaps in PR China and India, tend to use exotic species, mostly Indian and Chinese carps, which are known to grow fast and reach large sizes. There has not been a concerted attempt to assess the influences of these species on biodiversity in any nation, except for the preliminary study by Hossain et al. (1999) on stock enhancement in beels in Bangladesh described in Section 9.1. Even more disconcerting is that translocations of some of the above species within national boundaries are a common practice. More often than not, such translocations are not considered as "introductions", and any affects they may have on biodiversity receive little or no attention.

9.1 Biodiversity issues associated with floodplain fisheries stock enhancement

Floodplain waterbodies are neither riverine nor lacustrine, exhibiting features of both of these categories at some stage of their annual watercycle. The importance of floodplains as nursery, breeding and feeding grounds for many riverine fish species has been well documented. It is within this context that human interventions through physical changes to the floodplains and/or biological modifications such as through stock enhancement and introductions and transfers can impact biodiversity.
In the floodplain examples cited in the previous sections, stock enhancement activities have almost without exception involved exotic species, e.g. the use of Chinese carps and Java barb in Bangladesh and tilapia in Myanmar. Appropriate assessment of the biodiversity of floodplain fisheries is problematic, as they do not always have a permanent/resident fauna and the cyclical effects of flooding mean that this fauna changes according to the effects of inundation. To assess changes in biodiversity under such conditions is difficult, and to attribute the impacts of stock enhancement to any of these changes is even more problematic.
Hossain et al. (1999) conducted a study in three floodplain beel fisheries in Bangladesh from 1992 to 1995 that involved catches for 23 gear types (11 of which were selective). In this study, 41 species belonging 19 families (Table 30) were recorded (not taking into account species groups and two species for which the family status was not clear). Most importantly, only six species (including stocked species) were common to all three fisheries, clearly indicating the diversity of the fish fauna of the different floodplains. The authors used the Shannon-Weaver Index as a measure of diversity and concluded that (Table 31):

• in one beel (BSKB), fish diversity increased during the study period;
  
• the diversity index for all three beels varied from year to year;
  
• the stocked species dominated (by number) in the catches only once and in one beel only;
  
• the diversity index in two of the beels (Chanda and Halti beels) declined on termination of stocking with carp fingerlings; and
  
• overall, fish diversity declined significantly in one beel, remained unchanged in another and showed a small increase in the other beel.

In general, it is accepted that fish biodiversity of rivers and their associated wetlands is under severe threat. Welcomme (2000) suggested that perhaps the current threats make them the most endangered ecosystems on earth. Although the extent of stock enhancement of floodplain fisheries, and in particular, the use of exotic species for their enhancement, is not widespread in Asia, we know very little of the influence of this practice on biodiversity.
As the fragility of river and associated wetland ecosystems is increasingly perturbed through direct and indirect human intervention, the threat to the biodiversity of these systems is likely to increase. Stock enhancement offers opportunities for sustaining the productivity of some waterbodies - particularly those waterbodies whose fisheries have been impacted by environmental modifications or man-made structures such as reservoirs. This must be balanced against potential negative effects on biodiversity in other waterbodies that are still in a relatively unperturbed state and which still provide fisheries services through natural, unenhanced recruitment processes.
The study of Hossain et al. (1999) is perhaps the only attempt in Asia to discern a relationship between stock enhancement and fish faunal biodiversity, and it brings to focus the complexity of the problem and the serious lack of information relating to the issues concerned. With the current state of knowledge, it would be difficult, if not impossible, to draw general guidelines for future developments of stockenhanced fisheries of floodplains. Indeed, the only way this would become possible is through the commissioning of some relatively long-term studies on some of the significant floodplain fisheries of the region where stock enhancement is currently (or intended to be) undertaken.

9.2 Biodiversity issues related to stock enhancement in large lacustrine waters

The impoundment of rivers and streams brings about a reduction in biodiversity of the fish species of the impounded waters. This is due to the changes in flow regimes, barriers to spawning migrations, stratifications and altered trophic interactions. A recent study by Li (2001) on four representative reservoirs in PR China clearly showed a reduction in fish species biodiversity resulting from reservoir impoundment (Table 32). Another feature of impoundment is that, with the decrease in diversity, a few fish families tend to dominate the ichthyofauna. For example, in Danjiangkou Reservoir members of the family Cyprinidae account for 64.2 percent of all the species, whereas in the original river they accounted for only 44.2 percent. Similarly, only 12 families occur in the reservoir as opposed to 49 in the original river (Li 2001).

Table 30. Fish species recorded from three floodplain, stock-enhanced fisheries in Bangladesh. Based on data from Hossain et al. (1999); only data on identifications to the specific level are included

Family	Species	CB2	HB	BSKB
Anabantidae	Anabas testudineus			++
Aplocheilidae	Aplocheilus panchax		+
Badidae	Badis badis			+
Bagridae	Mystus cavasius		+	+
	M. tengara			++
	M. vittatus	++3	++
	Sperata aor	+		+
Belontidae	Xenetodon cancila	++
Channidae	Channa marulius		+	+
	C. punctata	++	++	++
	C. striata		+	++
Cobitidae	Botia dario		+
	Lepidocephalichthys guntea	+		+
Clupeidae	Corica soborna	+	++
	Gudusia chapra	+	++	+
	Tenualosa ilisha		+
Cyprinidae	Amblypharyngodon mola			+
	Barbonymus gonionotus1		+
	Catla catla		+
	Cirrhinus cirrhosus			++
	Ctenopharyngodon idellus1		+	+
	Cyprinus carpio1	++
	Labeo ariza	+	+	+
	L. gonius	+	+
	L. rohita			++
	Hypophthalmichthys molitrix1	+		+
	Rasbora daniconius	+	+
Gobiidae	Glossogobius giuris		++
Heteropneustidae	Heteropneustes fossilis	++		++
Mastacembelidae	Macrognathus aculeatus		+	+
	M. pancalus
Mugilidae	Rhinomugil corsula		++	+
Nandidae	Nandus nandus	++	+	+
Notopteridae	Chitala chitala	+	+	+
	Notopterus notopterus		+
Schilbeidae	Ailia coila			+
	Clupisoma garua	+	+
	Pseudeutropius atherinoides			+
	Silonia silondia		+
Siluridae	Ompok pabda			+
Sisordidae	Bagarius bagarius	+	+	+

¹ introduced species.
² CB - Chanda Beel, 10 870 ha; HB - Halti Beel, 16 770 ha; BSKB Beel, 26 040 ha.
³ ++ recorded among top five species at least once; + recorded at least once.

Table 31. Summary results of the Shannon-Weaver Index on fish species diversity, in different years, including (A) and excluding (B) stocked species, of the three floodplain beels (modified after Hossain et al. 1999)¹

SWI:	Chanda Beel				Halti Beel				BSKB Beel
Year:	’92	’93	’94	’95	’92	’93	’94	’95	’92	’93	’94	’95
Species	43	41	43	37	43	45	37	44	29	35	35	43
A	4.13	4.27	5.96	na2	4.27	3.94	na	na	3.5	3.66	3.53	4.14
B	3.69	3.55	5.96	4.05	3.98	3.41	3.41	2.72	2.49	2.82	2.89	3.30

¹ Note the number of species includes some species groups and hence, the discrepancy from Table 30.
² na = not available.

Table 32. Selected features of four reservoirs and the status of the fish fauna in comparison to the original river and the principal river system (modified from Li 2001)

Feature		Danjiangkou	Xinanjiang	Chanhshouhu	Hongmen
Original river		Hanshui	Xinanjiang	Longqi	Ganjiang
Principal basin		Yantze	Qiantangjiang	Yantze	Yantze
Year of impoundment		1967	1959	1955	1960
Size (ha)		62 000	53 333	4 470	6 900
Mean depth (m)		20.0	30.4	10.0	7.3
No. of fish species
	- Reservoir	67	83	40	69
	- Original river	75	102	20	na1
	- Principal basin	340	220	340	340

¹ na = not available.

Comparable reductions in the biodiversity of the ichthyofauna have been demonstrated in other countries. For example, in Hoa Binh Reservoir in northern Viet Nam, only 21 species have been recorded, whereas the river basin is purported to have 108 species (Ngo and Le 2001).
The loss of biodiversity in reservoirs cannot be avoided; it is an inevitable consequence of change from a riverine to a lacustrine habitat and the dam acting as a barrier to upstream movement of species. Conversely, it has been clearly shown that reservoirs have enabled increases in aquatic reptilian fauna and in fish-eating birds. Reservoirs are man-made habitats, and the more important question is whether the construction of a reservoir has resulted in a loss of biodiversity in the river that has been dammed and/or the principal river system of which the river is a part. The study of the effects of water management structures on river fisheries has been largely ignored during the initial environmental impact assessments, and it has only more recently been acknowledged that there have been wide ranging changes in the fisheries that were part of the systems affected.
More recent constructions have attempted to assess the effect of impoundments, but these have largely targeted the economic impact and/or overall production rather than the wider issue of species diversity. There is still a very poor understanding of how to balance the impacts of water management structures on fisheries and local livelihoods against the more wildly perceived benefits of income from electricity generation and irrigation. The reduction of the issues to gross economic returns often fails to capture relevant issues relating to people and their homes and the critical issue of long-term sustainability. A good example of this is the inappropriate application of aquaculture as mitigation for lost fishing livelihoods.
It is worth mentioning at this point that (typically cage) aquaculture is occasionally suggested as a means of offsetting the impacts on fisheries caused by dam closure or other changes to inland fisheries. The assumption is that the fishers can merely shift their activity to aquaculture. This simplistic approach is critically flawed for the following reasons:

• The aquaculture operation may often be geographically remote from the original fishing location (i.e. the loss of river fishing and requirement to move activities into the headpond behind a dam).
  
• The cost of the cages for aquaculture limits the ability of the great majority of fishers to change over to this activity.
  
• Fish in cages must be permanently guarded against theft, requiring a time investment that may have previously been used for other income generating/livelihood activities (this is rarely taken into economic calculations of the viability of aquaculture).
  
• The technical complexity of aquaculture is something that must be learned, making the activity highly risk prone in its early years.
  
• The establishment of aquaculture in a reservoir where there is a fishery means that marketing of the aquaculture product is in direct competition with the fish from the fishery, which may be lower priced or have a higher consumer preference (the result is that the aquaculture product may be more difficult to market profitably).

What is more relevant to the present study, however, is to assess whether stock enhancement in large inland waterbodies has been or is responsible for directly or indirectly influencing biodiversity. With the exception of PR China and Thailand, it can be generalized that the species used for stock enhancement of large waterbodies are almost always exotics. The issue then becomes more complex, as there are the double effects of the introduction of exotic species coupled to their effects on the existing species. This makes it very difficult to demonstrate cause and effect.
Perhaps the most controversial issue has been the introduction of exotic tilapias, most notably into Lake Lanao in the Philippines and their purported adverse affects on native cyprinids. Another example was the near extinction of a small endemic goby (the "sinarapan", Mistichthys luzonensis) in Lake Buhi, which is also suggested to be the result of the introduction of tilapia. De Silva et al. (2004) critically examined the available evidence on both cases and concluded that the exotic tilapia was not a primary factor in the decline of these indigenous species. This is evidenced by the fact that, with better management of the fishery activities in Lake Buhi, "sinarapan" is staging a recovery. More recently, Guerrero (1999) considered the influence of tilapias on the biodiversity of finfish in lakes and reservoirs in the Philippines and concluded that there had not been any adverse affects on the endemic fish fauna.
In Indonesia, the decline of the indigenous cyprinid Lissochilus spp., considered to have cultural importance, in Lake Toba, was attributed to the introduction of Oreochromis mossambicus to the lake (Baluyut 1999), although supporting evidence for this observation is not available.
Perhaps the primary reason that most stocked species (particularly the Chinese and Indian major carps) do not tend to influence the biodiversity of large inland, lacustrine waterbodies is that they are generally unable to reproduce in such waters and thereby form large populations that would compete for common resources. The accidental introduction of silver carp into Gobindasagar Reservoir (16 867 ha), Himachal Pradesh, is reported to have resulted in a marked decline in the fishery for indigenous major carps and other indigenous species and a concurrent dominance of silver carp, followed by grass carp and common carp. The contribution to the fishery from the latter group increased to 87.4 percent in 1989 from a meagre 14.2 percent in 1974-1975 (Sugunan 1995).
During this change, the importance of indigenous species, in particular Labeo dero, L. dyocheilus, L. bata, L. ariza and Barbodes sarana drastically declined, not necessarily a reduction in biodiversity per se, but a change that could lead to such a status in the future.
The exception to this is the tilapia, which readily establishes in large waterbodies and forms large self-sustaining populations. The case may be clearer for natural waterbodies; however, it is difficult to resolve the issue for large man-made waterbodies. In this case, it is necessary to determine the extent to which the tilapia is exploiting vacant niches within the artificial waterbody and the extent to which it is directly displacing indigenous species that may otherwise have established following the creation of the waterbody.

9.3 Biodiversity issues in culture-based fisheries

Except perhaps for the oxbow lakes in Bangladesh, all culture-based fisheries in the region are conducted in quasi-natural habitats. These are most commonly man-made waterbodies, some ancient and some relatively recent. Needless to say, these habitats are colonized to varying degrees by indigenous flora and fauna. However, the fish populations are not generally sufficiently large to support subsistence or artisanal fisheries on their own, and hence the secondary use of the waters for culture-based fisheries. From the earlier sections and previous reviews on the subject (De Silva 2003, Lorenzen 2003), it is evident that one other characteristic feature of these fisheries, with the exception of PR China, is that the practices depend either wholly or partially on exotic species. For example, the culture-based fisheries of Sri Lanka, Thailand and Viet Nam and to a lesser extent, India and Bangladesh, are based almost entirely on exotic species (Indian and Chinese major carps, common carp etc.).
As enhancement activities are most frequently conducted in quasi-natural waters, the apparent negative impacts on the biodiversity of the ‘indigenous’ flora and fauna of such waters cannot be strictly considered to be invasive as the environment has been artificially created. Indeed, the interactions and potential competition between exotic and native species in small waterbodies in the region have been barely studied. In one such study, in Sri Lanka, Wijeyaratne and Perera (2001) concluded that although some exotic and indigenous species shared common food resources, because of the nature of these food resources and their great abundance, there was no foreseeable competition per se between the two groups. This conclusion is supported by the study of Piet (1996).
Conversely, negative effects of culture-based fisheries could arise from exotic escapees invading the natural habitats of indigenous species, but there is no evidence yet that this has occurred. Since exotic species have been used for both fisheries enhancement and also aquaculture, it will be difficult, if not impossible to determine the specific effect of an enhancement activity. Despite this uncertainty, it is still important is to ensure that no new exotics are introduced for culture-based fisheries development per se and to make do with those species that are currently available. Additionally, it is preferable to explore the possibility of using other indigenous species, although economic considerations such as yield reductions that may result from this will have a strong influence on decisions.
There is an urgent need to address biodiversity issues in Asian waters, particularly in relation to fish species usage in stock enhancement practices. Not only are the direct affects of such practices important, but also their affects on the genetic diversity of the enhanced species brought about through generations of inbreeding. Unlike in aquaculture operations where there are deliberate efforts to prevent escapees of species with reduced genetic diversity, stock enhancement activities deliberately introduce hatchery-bred stocks (which may have similarly narrow genetic diversity to aquaculture stocks) to open environments where there is a greater probability of mixing with wild stocks, thereby increasing risks to the biodiversity of natural systems.

BANGLADESH FISHERIES SOCIETY: They're taking me to Bangladesh

BANGLADESH FISHERIES SOCIETY: They're taking me to Bangladesh

They're taking me to Bangladesh

 One big fish story

By: Beth                                              Tuesday, July 20, 2010

After our stay in the villages we traveled to the Grameen Fisheries. These  ponds were taken over from the Bangladeshi government because they were "derelict, full of debris and the aquatic vegetation was unfit for the fish culture". Grameen cleaned up the ponds and turned them over to the villagers to fish in them and take the fish to market. The objective is to make the villagers self sufficient, plus provide a constant food source. Many of them have no other income generating activity. The villagers catch the fish and take them to market. From the water they load about a dozen large barrels with fish and make the 1 1/2 hour trip to market.They receive 50 percent of the profit and Grameen gets the other 50 percent. Grameen's share is reinvested in the production of hatchlings, so there will continue to be fish in the ponds.

  While at the fisheries, while we were watching the men haul the nets in filled with fish, a local villager approached me and ask where I was from. "America," I replied. Then she asked if she could shake my hand, to which I graciously agreed.

BANGLADESH FISHERIES SOCIETY: EFFECT OF STOCKING DENSITY ON GROWTH AND PRODUCTION PERFORMANCE OF TILAPIA (Oreochromis niloticus L.) IN PONDS

BANGLADESH FISHERIES SOCIETY: EFFECT OF STOCKING DENSITY ON GROWTH AND PRODUCTION PERFORMANCE OF TILAPIA (Oreochromis niloticus L.) IN PONDS

EFFECT OF STOCKING DENSITY ON GROWTH AND PRODUCTION PERFORMANCE OF TILAPIA (Oreochromis niloticus L.) IN PONDS

ABSTRACT

The experiment was conducted to evaluate the effect of stocking density on the growth and production performance of tilapia (Oreochron:is niloticus) in ponds. Three stocking densities were used as 150, 200 and 250 fish/decimal and designated as treatment T1, T2 and T3 respectively having three replicates. All the fishes were of same age group having body weight of 12.5 g. A formulated feed (28.25% protein) was applied @ 5% body weight, at the beginning of the experimental period and reduced to 3% of their body weight and continued up to harvesting period. The result of the present study showed that the fish in the treatment T1 resulted with the best individual weight gain (124.37g) followed by treatments T2 and T3 respectively. The specific growth rates (SGR) are 2.65, 2.60 and 2.36 and the food conversion ratio (FCR) values arel.82, 1.77 and 2.04 in treatment T1, T2 and T3 respectively. There was no significant (P<0.05) differences among the survival rate of fishes which ranged from 94.2 to 96.99%. The fish productions were 18.09, 22.76 and 21.74 kg/decimal in treatments T1, T2 and T3, respectively. But the highest production 22.76 kg/decimal was obtained from the treatment T2 with a stocking density of 200 fish /decimal.

Key words: FCR, Growth, Production, SGR, Stocking density and tilapia

INTRODUCTION

Modern fish culture means improvement of culture practices through adopting different measures such as proper doses of fertilizer application, regular feeding, optimum stocking density, maintenance of physico­chemical factors, disease prevention and various control measures (Balarin and Hailer, 1982). The stocking density is the major concern for mono-culture. Some times excellent fish fry do not perform satisfactory growth unless correct stocking practices (Sanches et at 1999). In general the stocking density and growth of fish are very much related. The optimum stocking density ensures sustainable aquaculture providing proper utilization of feed, maximum production, sound environment and health. In comparison to low stocking density, high stocking density exerts many negative impacts such as competition for food and shelter and rapid out break of disease if occurred. Therefore it is important to optimize the stocking density for the target species in aquaculture for desired level of production. Tilapia has good resistance to poor water quality and disease, tolerance to a wide range of environmental conditions, ability to convert efficiently the organic and domestic waste into high quality protein, rapid growth rate and good flavour (Ballarin and Hallar, 1982). Tilapias are currently having important impacts on poor people in developing countries, both as cultured species in household-management systems and through access to fish produced in informal and formal fisheries (Edwards, 2003; and Little, 2003). But the culture practice of tilapia varies to a great extent from country to country and even among the different farming systems.

In view of above facts, the present experiment was undertaken to achieve the following objectives, to study the effect of stocking density on the growth and production performance of tilapia in ponds and determine the suitable stocking density for culture of tilapia in ponds.

MATERIALS AND METHOD

Study area

The experiment was carried out during the period from 151 March to 30th May, 2007 in ponds located at the South-West corner of the Faculty of Fisheries, Bangladesh Agricultural University, Mymensingh.

Pond preparation ,

The pond dykes and embankments were raised and repaired properly in broken places and unwanted species was removed by-using rotenone @ 50 gm/decimal. After one week ponds were limed at a dose of 1 kg/decimal and fertilization of the pond was done with cow-dung, urea, and TSP (Triple Super Phosphate) @ 7 kg/decimal, 100gm/decimal and 100gm/decimal respectively.

Experimental design and stocking

The experiment was conducted in 9 mini ponds with three treatments in CRD i.e. T1, T2, and T3 each having three replications. The ponds were stocked with 150, 200 and 250 tilapia fingerlings per decimal in T1, T2 and T3.

Post stocking management

Fertilization

Fertilization of the ponds was done fortnightly with cow dung, urea and triple super phosphate (TSP). Cow dung was applied Q 3 kg/ decimal and urea and TSP fertilizers were applied @ 40 g /decimal. Urea and TSP were applied after dissolving them in water in a bucket and then spreaded over the pond surface manually.

Feeding

Throughout the experiment supplemental feed which contains 28.25% protein was given at the rate of 5% (151 month), 4% (2nd month) and 3% up to harvesting of their body weight. The feed was supplied in the dried form and feeding was done directly without any feeding trays. Half of the ration was supplied at 8.00 am and remaining half was supplied at 4.00 pm.

Water quality parameter monitoring

The four major water quality parameters such as water temperature, dissolved oxygen, transparency and pH were measured at 9 am by using a commercial kit box (Model: FF-3, USA) at monthly intervals.

Growth and production monitoring

The growth and production of fishes were measured monthly through random sampling method. The weight of fish (in gm) was measured by using a portable balance (Model: OHAUS) and were calculated by following formula.

Weight gain (g) = Mean final weight (g) -mean initial weight (g)

   Mean final fish wt - Mean initial fish wt.

(%) Weight gain =  _________________________________________ x 100

Mean initial fish wt.

                                                          ).

Specific Growth Rate, (SGR%  per day) = (Log, W_Z -Log, W,  ____ x 100

T, - T_z

Where, W1= the initial live body weight at time T1 W2⁼ the final live body weight at time T2 Tz_ Ti = Duration of the experiment (day)

Food conversion ratio (FCR) = Feed fed (dry weight). x 100 Live weight gain Survival (%) = No^-.of fish harvested.

x100

No. of fish stocked

Production = No of fish harvested ^x Final weight of fish Data analysis

Analysis of the data was done by using the software SPSS (Statistical Package for Social Science) version 11.5 significance was assigned at 0.05% level.

                                                                                                                                                                   

RESULTS AND DISCUSSION

Water quality parameters

The results of the water quality parameters such as temperature, pH, dissolved oxygen and transparency during the experimental period are presented in Tables 1 and Fig. 1.

Transparency

Water transparencies of the experimental ponds under different treatments are presented in Table 1.The mean values of transparency were 30.653.43, 31.751.08 and 35.7(5.6) for treatment T1, T2 and T3 respectively. There was no significant variation of transparency among different treatments. The present findings agreed with the findings of Kohinoor (2000) who recorded transparency values ranging from 15 to 58 cm. Wahab et al. (1994) found transparency ranging from 15 to 75 in polyculture pond. Rahman (1992) concluded that the transparency of productive water bodies should be 40 cm or less.

Water Temperature (°C)

During the study period, the water temperature varied from 26.65°C to 29.65°C in Tt , 26.60°C to 30.10°C in T2 and 26.65°C to 29.10°C in T3 (Table 1). The mean values of temperature in TI, T2 and T3 were 30.03 3.25, 28.623.52, and 27.533.20 respectively. Dewan et al. (1991) recorded the water temperature ranged from 29.3 to 34.OoC whereas Kohinoor (2000) observed the water temperature ranged from 24.2 to 33.3⁰C. So the results of this study were similar to the findings of above authors.

Table 1. Average (Mean±SD) values of water quality parameters under different treatments throughout the study period

Treatment	Water	temperature (°C)	Dissolved	oxygen	(mg/L)		pH	Transparency (cm)
Ti		28.46.38		5.630.	56		7.860.31		30.653.43
T2		28.62.52		5.710.51			7.950.30		31.754.08
T3		27.53.50		5.160.74			8.490.62		35.715.61

Figures indicates mean values lstandard deviation

 

TI

T2

Treatments

T3

Fig I Average value of water quality parameters under
different treatments throughout the study period

Dissolved Oxygen

During the study period, the dissolved oxygen contents of water were varied from 4.85 to 6.65 mg/L in T1, 5.10 to 6.65 mg/L in T2 and 4.35 to 6.65 in T3 (Table 1). The mean values of dissolved oxygen content obtained in treatments T₁, T2 and T3 were 5.63 #3.56, 5.71, ± 0.51, 5.16, X1.74. Wahab et n1. (1995) recorded DO ranging form 2.2 to 7.1 mg/L in nine ponds of Bangladesh Agricultural University Campus, Mymensingh, while Kohinoor (2000) measured DO 2.0 to 7.9 mg/L in the seasonal ponds of BAU Campus, Iviy>nensingh.

                                                                                                                                                                 

. pH

The pH values under different treatments are presented in (Table 1). During the study period, the range of pH values recorded in treatment T₁. Tz and T3 were found to vary between 7.35 to 8-05, 7.55 to 8.15 and 7.55 to 9.25 respectively. The mean values of pH obtained in the treatments T1, T2 and T3 were 7.86fl.31, 7.958.30 and 8.4937.62 respectively (Fig. 1). Hussain ( 1997) found pH 6.7 to 8.3, while Kohinoor et al. (1998) reported pH 7.2 to 7.3 in the research ponds of BAU Campus, Mymensingh.

Growth performance offish

For the evaluation of growth performance of fish in different treatments in terms of initial weight gain, specific growth rate (SGR% per day), food conversion ratio (FCR), survival rate (%) and production (kg/decimal/90 days) were calculated and are shown in Table 2. The present experiment showed the highest mean weight gain of fish in treatment Tl which was stocked at lower densities although same feed and feeding rate were applied in all the treatments.

Weight gain            _

No significant (PO.05) variation was recorded in initial weight of fish under different treatments (Fig. 2). The mean weight gain of fish at the end of the experiment was significantly higher in Tl (124.375 g) than those of treatments Tz (118.6 g) and T3 (92.35 g). The mean lowest weight gain was obtained in T3 treatments which stoking rate was 250 fish/decimal. Kohinoor et al. (1998) obtained the highest growth of tilapia stocked at the rate of 80 fish/decimal fed with supplemental feed compared to those which received only fertilizer application.

160

--*--T1     -a--T2      -*-- T3

140 -

 

120 - 100

-

rn

o, 80 -

--_y

3 so -

40 - 20 -

a

60

90

30          45

Days

Fig 2. Growth of tilapia into rms of increase in weight (g) in
diffarent treatments during the experimental period

75

0

15

Specific growth rate (SGR) and Food Conversion Ratio (FCR)

The mean specific growth rate of tilapia in different treatments ranged between 2.363 to 2.655. The significantly (P< 0.05) highest SGR values (2.65) was recorded in treatment Ti while the lowest (2.363) was obtained in T3. In the present study, the food conversion ratio was higher (2.04) in treatment T3 than T1 (1.82) and T2 (1.77) treatments.

Survival rate and production of fish

The survival as recorded in the present study was fairly high which ranged from 94.2 to 96.99% (Table 2). The survival rate recorded in present study is higher that the survival rate recorded by Hussain et al. (1987), which might be attributed to the relatively larger size of fingerlings (12.5 g) stocked in the present study. Although the mean weight gain in treatment T1 was the highest, the total yield of fish were highest in

treatment T2 followed by treatment Tl which is due to the higher stocking density i.e. the higher number of fish used in treatments T2 and T3 (Fig. 3). The present results supports the findings of Dirnitroy (1976) who achieved the best production from higher stocking densities (80 fish/m3) when compared to that achieved with the lower ones (15 and 50 fish/m3). Thus, the results of the present study indicated that a stocking density of 200 fish per decimal is optimum for tilapia culture in ponds.

Table 2. Growth parameters of tilapia observed in different Treatments

Growth		Treatment
parameters	T1	T2	T3
Mean initial weight (g)	12.50-(@))	12.50 a (8)	12.50 a (ffi)
Mean final weight (g)	136.87a (8.17)	131.10 b (8.56)	104.85 r(fl.21)
Weight gain (g)	124.37- (8.17)	118.60 n (8.56)	92.35 x(8.21)
Weight gain	995.00 a (4.41)	948.80 n (4.52)	778.80 c (1.69)
SGR (% per day)	2.65 a (01.0071)	2.60 b (8.0071)	2.36 c (8.0021)
FCR	1.82 b (8.0085)	1.77 1 (8.0148)	2.04 a (8.0141)
Survival rate (%)	96.99 a (8.47)	96.00 a (8.70)	94.20 a (8.84)
Fish production (kg/decimal/90 days)	18.09 b (8.11)	22.76 x(8.28)	21.74 x(8.14)

*Values in the same row having the same superscript are not significantly different (P<0.05), values are given with t standard deviation

 

CONCLUSIONS'

By concluding the conducted study the effect of stocking density on the growth and production .performance of Tilapia in ponds fed with formulated diet for a period of three months in nine experimental ponds, the different issues related to experiment i.e. the water quality parameters such as temperature, dissolved oxygen, pH and transparency and growth performance of fish in different treatments in terms of initial weight gain , specific growth rate (SGR% per day), food conversion ratio (FCR), survival rate (%) and production (kg/decimal/90 days) were calculated, analyzed and discussed. From the experiment it may be suggested that the optimum stocking density (200 fish/decimal) performs the better results.

                                                                                                                                                                  REFERENCES

Balarin, J. D. and R. D. Haller. 1982. The intensive culture of Tilapia in tanks, raceways &ages, P. 265-355. In J. F. Muir 8R. J. Roberts (eds.). Recent advances in Aquaculture. West view press. Boulder, Colorado, USA.

Dewan, S., M. A. Wahab, M. C. M. Beveridge, M. H. Rahman and B. K. Sarker. 1991. Food selection, selectivity and dietary overlap among planktivorous Chinese and Indian major carp fry and fingerlings grown in extensively managed, rain fed ponds in Bangladesh. Aquaculture and Fisheries Management, 22: 277-294. -

Dimitroy, M. 1976. Carp culture in net cages. FAO Aquaculture Bull., 8 (1) : 8-16.

Edwards, P. 2003. Role of tilapia in rural Aquaculture. Global Aquaculture Advocate, February-2003. 59-61 pp. Hussain, M. G. 1997. Studies on production, growth and survival of Tilapia area in Syrian experimental

ponds. UNV multi-sectoral Asst. project SYR/78/077. United nations Development programme,

Damascus, Syria.

Hussain, M. G., M. A. Rahman and M. Akteruzzaman. 1987. A study on the production of O. niloticus
(Linnaeus) under semi-intensive system in Bangladesh. Bangladesh J. Fish. Res., 1 (2) :19-23.

Kohinoor, A. H. M. 2000. Development of culture technology of three indigenous fish mola (Ani6lyphnryngodon niola), Punti (Puntius sophore) &hela (Chela crtchius) with notes on some aspects of their biology. Ph. D. dissertation. Department of Fisheries Management, Bangladesh Agriculture University, Mymensingh. 363.

Kohinoor, A. H. M., P. C. Modak and M. G. Hussein. 1998. Growth and production Performance of red Tilapia

and Nile Tilapia under low input culture system. Bangladesh J. Fish. Res., 3 (1):11-17.

Little, D. C. 2003. Meeting the needs of the. poor in Asia- Tilapia in the new millennium. Striling, U.K. Institute

of Aquaculture, University of Stirling.

Rahman, A.K.A. 1992. Tilapia in Bangladesh. In: E.A. Balayut (ed.), Paper Contributed to the Workshop on Tilapia in Capture and Culture enhanced Fisheries in the Indo-Pacific Fishery Commission Countries 27-29 June, 1991, Bogor, Indonessia. FAO Fisheries Report No. 458, Supplement, FAO, Rome, 139­142.

Sanches, L.E.F. and C. Hayashi. 1999.Stocking density effect on Nile Tilapia (0. niloticus) fry performance during sex reversal. Acta seientiarum. 21(3): 619-625.

Wahab, M. A.1 Z. F. Ahmed, A. Islarn and S. M. Rahmatullah. 1995. Effect of introduction of common carp, Cyprinus carpio (L) on the pond Ecology and growth of fish in polyculture. Aquacult. Res.26: 619-628.