Olive barb, Puntius sarana (Hamilton) is a potential candidate species for introduction into the grow-out carp polyculture system

The compatibility of olive barb, Puntius sarana (Hamilton) with major carps was studied in grow-out carp polyculture system for one year in a set of nine earthen ponds of 0.08 ha each. Three different species combinations evaluated were Control: catla (Catla catla Ham.), silver carp (Hypophthalmichthys molitrix Valenciennes), rohu (Labeo rohita Hamilton) and mrigal (Cirrhinus mrigala Hamilton) at 0.5:0.5:1:1; T1: catla, silver carp, rohu and olive barb at 0.5:0.5:1:1 and T2: catla, silver carp, mrigal and olive barb at 0.5:0.5:1:1 at combined density of 7500 fingerlings/ha. While survival levels of the carps did not differ significantly in treatments (P > 0.05), silver carp recorded highest survival levels (94–96%) followed by olive barb (87–90%), mrigal (72–74%), rohu (72–73%) and catla (67–69%). The specific growth rate (SGR) and average harvested body weight (ABW) of catla and silver carp did not differ significantly among the treatments revealing their competition with mrigal or olive barb to be minimum. In absence of rohu in T2, both mrigal and olive barb showed higher SGR and ABW revealing minimal competition between these two species, while their lower performance in presence of rohu in Control and T1 indicated inter-specific competition with the latter. Such olive barb–rohu inter-specific competition, however, failed to yield significant effect on growth of rohu as revealed from its non-significant SGR difference in presence and absence of olive barb. The lower FCR (2.54 ± 0.06) and higher treatment biomass production (3418.4 ± 95.0 kg ha^− 1 year^− 1) in T1 with rohu–olive barb combination compared to T2 with mrigal–olive barb (2.84 ± 0.11; 3155.1 ± 104.7 kg ha^− 1 year^− 1) indicated feasibility and advantage of culturing rohu with olive barb rather than mrigal in carp polyculture. Further, similar biomass production in Control and T1 also indicated feasibility of replacing mrigal with olive barb in the grow-out carp polyculture system.     

Evaluation of minor carps intercropping in carp polyculture vis‐à‐vis other grow‐out cropping patterns of carp farming

One year grow‐out evaluation of four cropping patterns of carps, viz. control: single stock single harvest (SSSH); T‐1:intercrop of minor carps and Indian major carps (IMC); T‐2:single stock multiple harvests (SSMH); and T‐3:multiple stock multiple harvests (MSMH) was conducted in eight earthen ponds (0.09 ha each). Ponds were stocked with three IMCs (catla, rohu and mrigal) at 1:1:1 ratio at 10,000 fingerlings/ha combined density. T‐1 was additionally stocked with 10,000 fingerlings/ha of minor carps (Puntius gonionotus, Labeo fimbriatus and Puntius sarana), while T‐2 with additional 10,000 fingerlings/ha of the IMC. Periodic removal of partial biomass ensured prevalence of better water quality in treatments (higher water pH, higher dissolved oxygen and reduced inorganic nutrients). It helped to improve fish growth as average harvested weight of rohu and mrigal remained similar in treatments despite the presence of greater inter‐ and intraspecific competitions in intercrop and SSMH, respectively, and periodic stocking of younger juveniles in MSMH. Catla showed significantly higher growth in MSMH. The biomass yield in intercrop, SSMH and MSMH were 21%, 17% and 24% higher than SSSH, but the respective net incomes were 32.9, 21.3 and 56.5% higher. Partial harvest also helped reducing FCR in the order T‐3<T‐2<T‐1<control. While the study showed MSMH as the most productive cropping pattern for biomass yield, the intercrop of minor carps and IMCs proved to be the most water productive (gross and consumptive water use) cropping method to produce varied fish protein with higher biomass yield.     

Compatibility of silver barb Puntius gonionotus (Bleeker) with Indian major carps in a grow-out polyculture

The compatibility and growth performance of silver barb Puntius gonionotus (Barbonymous gonionotus) with the three Indian major carps, i.e., Catla catla, Labeo rohita and Cirrhinus mrigala, were assessed in a 10‐month carp polyculture trial. Treatments T‐1, T‐2, T‐3 and T‐4 were stocked with three of the above four carp species, with an absence of silver barb, mrigal, rohu and catla, respectively, while all four species were stocked in treatment T‐5. The treatments were stocked at 6000 fingerlings ha⁻¹, with an equal species ratio maintained in each treatment. Incorporation of silver barb into the polyculture system neither affected the survival of any carp irrespective of species combination nor yielded significant changes in biomass production among treatments, except for the one without catla, where it was significantly low. The study revealed a higher extent of competition between silver barb and rohu, perceptible from the lower growth of one in the presence of the other. Although a certain level of competition of silver barb with mrigal was evident, competition with catla was not perceptible. Irrespective of species combination with silver barb as a component species, similar total biomass production in treatments revealed the feasibility of its incorporation into the Indian major carp‐based polyculture practice without affecting the total yield.     

Grow‐out performance of Kuria labeo,Labeo gonius (Hamilton), with major carps in carp polyculture system

A year‐long grow‐out carp polyculture trial was conducted in nine earthen ponds to study the growth performance of Kuria labeo (Labeo gonius) with the different major carps such as catla (Catla catla), silver carp (Hypophthalmichthys molitrix), rohu (Labeo rohita) and mrigal (Cirrhinus mrigala). Suitable water quality parameters were maintained in ponds through intermittent liming, manuring and fertilization. Three different species combinations of carps were evaluated using silver carp and catla as the common species and varying other carp components as rohu–Kuria labeo, mrigal–Kuria labeo and rohu–mrigal in the three treatments. The ponds were stocked at a combined density of 7500 fingerlings ha^?1. Silver carp and catla showed similar growth performances in all the three combinations, suggesting that other carps in the combination do not have any differential influence on their growth. Kuria labeo was compatible with rohu, while competition was observed with mrigal. Although growth performance of Kuria labeo was inferior to that of mrigal, better compatibility of Kuria labeo with rohu helped this combination to yield a biomass equivalent to the mrigal–rohu combination, suggesting feasibility to use Kuria labeo as an alternative species to mrigal in the major carp polyculture system without compromising the total biomass yield.     

Over-wintering growth of Macrobrachium rosenbergii (de Man) with carp polyculture in Bangladesh fed formulated diets

An experiment was conducted from December 2003 to April 2004 to observe the over‐wintering growth of freshwater prawn, Macrobrachium rosenbergii, with catla, Catla catla and rohu, Labeo rohita in polyculture using formulated diets. The study was conducted in eight experimental ponds, each 80 m². Three experimental diets containing 30% protein were prepared using fish meal, meat and bone meal, mustard oilcake, rice bran, wheat bran and molasses (binder), and assigned to treatments T₁, T₂ and T₃ respectively. A commercial diet from Saudi‐Bangla Fish Feed was assigned to T₄ (reference diet). Each treatment had two replicate ponds. Juvenile prawns and catla and rohu fingerlings (initial weight 1.60±0.10, 30.0±1.2 and 25.0±1.1 g respectively) were stocked at a ratio of 2:1:1 (prawn:catla:rohu). A total of 160 prawn and fish (20 000 ha^?1) were stocked in each pond. Fish were fed twice daily at 3% body weight (b.w.) for the first 3 months and 5% b.w. for the last 2 months. Prawns in T₁ fed diet 1 had significantly higher (P<0.05) weight gain compared with that of T₃. The reference group and T₂ had intermediate values not significantly different from either. Weight gains of catla and rohu were significantly higher in T₁. The feed conversion ratio values of different diets ranged between 1.89 and 2.13. Survival (%) ranged from 90.0% to 95.0% for catla, 87.5% to 92.5% for rohu and 70.0% to 76.3% for M. rosenbergii, and there were no significant differences (P>0.05) among different treatments. Total production ranged between 2196 and 2679 kg ha^?1, with T₁ showing significantly higher production and net profit (taka 56 531.9 ha^?1). The results of the study demonstrated that it is possible to culture M. rosenbergii with carp in polyculture during the winter utilizing the late‐produced PLs. Further study is needed to determine the optimum stocking density of M. rosenbergii in carp polyculture.     

Influence of duration of aeration on growth and survival of carp fingerlings during high density seed rearing

Impact of varied durations of aeration on growth, survival and production performances of catla (Catla catla), rohu (Labeo rohita), fringe lipped carp (Labeo fimbriatus) and olive barb (Puntius sarana) were evaluated in outdoor concrete tanks (10 m × 5 m × 1.3 m) during fingerlings rearing. At a combined stocking density of 0.5 million fry/ha, provision of night time aeration for 4, 8 and 12 h was evaluated as the three treatments, T-I, T-II and T-III, respectively against control (T-c, without aeration). Overall survival and net biomass of the species increased among the treatments significantly as a function of aeration hours (T-c < T-I < T-II < T-III). Aeration for 8 and 12 h showed significantly higher survival, harvested body weight and SGR in all the carps than those with 4 h (T-I) and no aeration (T-c), suggesting 8–12 h of aeration requirement for fingerlings rearing at such high density. Further, no significant difference between survival levels in T-II and T-III groups suggested 8 h of aeration to be adequate. However, while species-wise performance showed 8–12 h night time aeration to be advantageous for catla and rohu, aeration for 4 h was adequate for fringe lipped carp and olive barb.     

Effects of varied levels of incorporation of Labeo gonius in carp polyculture system in India

Growth performance of kuria labeo, Labeo gonius as a component species in the major carp polyculture system was evaluated at two incorporation levels against a control without the species through a year‐round grow‐out study in nine earthen ponds (0.08 ha). Three species ratio of catla, silver carp, rohu, mrigal and kuria labeo at 15:15:40:30:0 (T‐1: control), 15:15:40:20:10 (T‐2) and 15:15:40:10:20 (T‐3) were evaluated as three treatments. The carps were stocked at a combined density of 7500 fingerlings ha^?1. Silver carp demonstrated the highest survival (75–81%) followed by rohu (70–76%), catla (69–76%), kuria labeo (69–71%) and mrigal (67–69%). Species‐wise yield attributes such as survival, harvest weight, SGR and biomass yield of silver carp, catla and rohu were similar in their respective treatments. Kuria labeo at 10% inclusion demonstrated 12% higher harvest weight than its 20% inclusion. However, such higher weight gain could not affect the total biomass yields of carps which remained similar among the treatments. Furthermore, harvest weight of kuria labeo at 10% inclusion was comparable to that of mrigal when the latter incorporated at 20–30% level. Therefore, the study suggested 10% to be a suitable incorporation level for kuria labeo in the commercial grow‐out carp polyculture system.     

Polyculture of Thai pangus (Pangasius hypophthalmus,Sauvage 1878) with carps and prawn: a new approach in polyculture technology regarding growth performance and economic return

An experiment was conducted during May to December 2002 to determine growth performance, the highest economic return and suitable species composition in the polyculture of Thai pangus (Pangasius hypophthalmus) with carps (catla, Catla catla and rohu, Labeo rohita) and freshwater giant prawn (Macrobrachium rosenbergii) using low‐cost formulated feed. Three treatments (T₁, T₂ and T₃) were conducted with three replications. The treatment T₁ was designed as a monoculture of pangus with a stocking density of 17 500 individual ha^?1. The other two treatments (T₂ and T₃) were designed as polyculture and stocked with pangus, catla, rohu and prawn with densities of 10 000, 2500, 5000, 3750 ha^?1; and 10 000, 5000, 2500, 3750 ha^?1 in T₂ and T₃ respectively. The net weight gain and production of pangus were significantly different (P>0.05) between monoculture and polyculture but were not different within the two polyculture systems. The production of catla and rohu were significantly different (P>0.05) in both treatments where prawn was not. Though the gross production (8.53 ton ha^?1) was significantly (P>0.05) higher in T₁, the higher gross net profit (Tk 154 201 ha^?1) was in T₂. Thus, the polyculture of pangus is more profitable than its monoculture and the species composition in T₂ is more suitable than other composition.     

Effects of increasing the stocking density of large carps by 20% on 'cash' carp–small fish polyculture of Bangladesh

This experiment was carried out in the framework of a project to develop a viable fish polyculture technology under Bangladeshi conditions that allows simultaneous fish production of small indigenous species for the farmers' family consumption and of large carp species as a cash crop. The objectives of this experiment were to assess the effects on fish performance and on the environment of adding 20% large fish to the basic ‘cash crop’ carp–small fish polyculture consisting of 10 000 fish ha^?1 of the large carp rohu Labeo rohita (Hamilton), catla Catla catla (Hamilton) and common carp Cyprinus carpio (L.) at a species ratio 1:1:1, and 15 000 fish ha^?1 of each small indigenous fish punti Puntius sophore (Hamilton) and mola Amblypharyngodon mola (Hamilton) (control). The treatment ponds were stocked with additional 2000 large fish ha^?1, either all rohu, or all catla, or all common carp, or half rohu and half common carp, or half catla and half common carp. The results obtained and the analysis of interactions through the food web that affect food resource availability of the different fish species and account for the trends and differences observed among treatments confirm the positive effect of common carp on rohu reported in previous experiments and show that a 20% increase in large carps stocking neither affect the survival of the large carps nor reduce harvesting biomass of the small fish for the farmer's family consumption. Increased stocking densities of each large carp species did not significantly reduce its own harvesting weight and mean growth rate, while significantly increased rohu and catla (but not common carp) harvesting biomass and yield. The complex relations between species led to inter‐ and intraspecific competition, which in some treatments increased growth or yield of one species and in other treatments of other species, so that the gains on one species and the losses on the other led to no significant total harvested biomass differences between treatments. Yet, the results herein reported may help farmers to select their species stocking ratios. Thus, if the main target of the farmer is rohu, then a stocking density increase of 10% common carp and 10% rohu would improve rohu growth rate (due to common carp) and result in 50% higher rohu harvesting biomass and yield. If the main target of the farmer is catla, then a 20% increase in catla stocking density would lead to 20% higher catla harvesting biomass.     

Evaluation of Growth,Survival, and Production of an Endangered Fish,Labeo gonius (Hamilton) Fingerlings in Earthen Nursery Ponds

ABSTRACT

Nursery rearing of an endangered fish, Labeo gonius (Ham.) was studied in relation to varying stocking densities in earthen ponds. The experiment was conducted for 8 weeks in nine nursery ponds having an area of 0.012 ha with an average depth of 1 m. Four-day-old hatchling stocked at 0.6 million/ha was designated as treatment-1 (T₁), 0.8 million/ha as treatment-2 (T₂) and 1.0 million/ha as treatment-3 (T₃), respectively. At stocking, all hatchlings were of same age group with a mean length and weight of 0.66 ± 0.08 cm and 0.001 ± 0.0001 g, respectively. Hatchlings in all the experimental ponds were given wheat flour for the first 7 days, finely ground mustard oilcake for the next 7 days and a mixture of rice bran, and mustard oilcake (1:1) for days 15 to 56. The rate of feeding was 20 kg/million hatchling/day for the first two weeks, 25 kg for the second two weeks, 30 kg for the third two weeks and 35 kg for the fourth two weeks. The physicochemical parameters of water and plankton were monitored simultaneously and were within the acceptable range for fish culture. Growth parameters (final weight, final length, weight gain, length gain and specific growth rate) and survival of fingerlings were significantly higher in T₁ (0.6 million hatchling/ha) than those in T₂ (0.8 million/ha) and T₃ (1.0 million/ha), respectively. Feed conversion ratio (FCR) was significantly lower in T₁ followed by T₂ and T₃ in that order. The estimated gross and net productions of fingerlings were significantly higher in T₁ than in T₂ and T₃, respectively. Significantly higher number of fingerlings was produced in T₃ than those in T₂ and T₁. Despite this, consistently higher net benefits were obtained from T₁ than from T₃ and T₂. Overall, highest growth, survival, production and benefits were obtained from T₁ where stocking density of hatchlings was 0.6 million/ha. Hence, of the treatments evaluated, stocking density of 0.6 million hatchling/ha appears to be the most efficient stocking density for rearing of L. gonius fingerlings in earthen nursery ponds.     

Optimization of stocking density of freshwater prawn Macrobrachium rosenbergii (de Man) in carp polyculture in Bangladesh

A study was conducted to optimize stocking density of freshwater prawn, Macrobrachium rosenbergii, in carp polyculture for 3 months in 10 experimental ponds of 80 m². Five stocking densities of prawn, 2500, 5000, 7500, 10 000 and 12 500 ha^?1, were assigned to treatments T₁, T₂, T₃, T₄ and T₅ respectively. The densities of catla, Catla catla, rohu, Labeo rohita and silver carp, Hypophthalmicthys molitrix, were 2500, 5000, and 2500 ha^?1, respectively, in each treatment. Each treatment had two replicate ponds. The mean initial weights of prawn, catla, rohu and silver carp were 1.1±0.02, 8.28±0.1, 25.2±1.1 and 36.32±1.2 g respectively. A pelleted diet containing 30% protein was prepared using fish meal, meat and bone meal, mustard oilcake, rice bran, wheat bran and molasses, and was fed twice daily at a rate of 5% of fish biomass. Water quality parameters were measured fortnightly and the ranges of temperature, pH and dissolved oxygen were 27.5–1.3°C, 6.9–8.6 and 4.5–8.6 mg L^?1 respectively. Feed conversion ratios ranged from 2.05 to 2.20 among the treatments. Per cent survival (%) of prawns ranged from 72% to 78%, while it varied from 80% to 93%, 90% to 95% and 90% to 92% for catla, rohu and silver carp respectively. The results showed that there were no significant differences among the weight gains of prawn and carp in different treatments. However, the overall total production of prawn and fish together was significantly (P<0.05) higher in T₃ and T₄ compared with other treatments. The total production for 3 months ranged between 2618 and 2916 kg ha^?1. The production of prawn was significantly higher (361.3 kg ha^?1) in T₅ with a highest stocking density of 12 500 prawn ha^?1. Although there was no significant difference (P>0.05) between the total production of prawn and fish together in T₃ and T₄, the highest net profit (Tk. 69 006 ha^?1) was obtained in T₄. Therefore, from the result of the study it may be concluded that a stocking ratio of 4:1:2:1 of prawn:catla:rohu:silver carp at a total density of 20 000 ha^?1 may be recommended for prawn–carp polyculture in ponds.     

Integrated Duck-cum-Fish Farming in Bangladesh

An experiment on integrated duck-cum-fish farming was conducted in 11 ponds of 0.1 ha each at the Fisheries Research Institute, Mymensingh, Bangladesh. Khaki Campbell layer ducks Anas platyrhychos were housed directly over the pond water surface at 200, 400 and 500 dncks/ha. Each density had three replicate ponds and two ponds had no ducks. Fish fingerlings were stocked at a total density of 8,850/ha. The species composition was silver carp Hypophthalmicthys molitrix 33.9%; catla Catla catla 12.4%; rohu Labeo rohita 18.1%; mrigal Cirrhina mrigala 28.8%. grass carp Ctenopharyngodon idella 1.4% and sor puti Puntius gonlonotus 5.4%. The fish were not given any supplemental feed, and the ponds were not fertilized except for the split duck feed and duck manure falling directly into the ponds. Ducks were fed with a feed formulated from locally available ingredients.
After one year the fish were harvested. The yield of fish increased with an increase in duck density. Highest net fish production of 4,250 kg/ha/yr was obtained from ponds with 500 ducks/ ha, compared to 490 kg/ha/yr from the control ponds. Manure of each duck contributed a net fish yield of 6.9–7.5/yr. Average egg production was 237 eggs per female duck per year. Economic analysis of the technology showed a net profit of about 100% of the total costs, indicating the economic viability of the technology.     

Effects of silver carp and the small indigenous fish mola Amblypharyngodon mola and punti Puntius sophore on fish polyculture production

A sustainable semi-intensive pond aquaculture technology including major carp species as cash-crop and small indigenous fish species (SIS) as food for the farmers' families is being optimized in Bangladesh. The inclusion of silver carp (Hypophthalmichthys molitrix), a cheap large species affordable by poor farmers, is now being considered. As part of a study on the effects of this filter feeder on polycultures including the large carps rohu (Labeo rohita), catla (Catla catla) and common carp (Cyprinus carpio) and the SIS punti (Puntius sophore) and mola (Amblypharyngodon mola), an experiment was carried out under farm conditions to test the effects of silver carp and of each SIS species on the growth, survival and yield of the large and small species and on pond ecology.The experiment was performed in 38 farmers' fishponds of different sizes, from 220 m² to 1200 m². The results show that the larger the fish pond the better rohu performance, the larger punti fry weight and the lower punti fry harvested biomass. Pond size did not affect other fish species. The addition of 250 mola and/or punti per 100 m² fishponds affected rohu and catla and did not affect common and silver carps. The addition of mola alone reduced rohu's parameters by 15%. The addition of SIS in the three combinations tested (250 mola, 250 punti, 125 of each species) reduced catla's parameters by 20-24%. Punti fry were larger when both SIS were stocked and punti fry biomass was larger when only punti were present. Total mola harvested biomass and yield were larger when the entire SIS stocked were only mola.The addition of 10 silver carp over the 99 large carps stocked per 100 m² fishponds negatively affected rohu and catla growth and yield by about 15-21% and 45-50% respectively but not their survival, did not affect common carp performance, did not affect punti and mola reproduction in the ponds, reduced punti yields by 25%, reduced mola performance by about 35%, and silver carp own biomass increased total yield and total income in about 12% each. These effects are explained and discussed considering fish interactions through the food web. The decreased income from selling the more expensive large carps is more than compensated by that obtained from silver carp, which allows the option to the farmer to sell part of the silver carp to complete the cash income that would have been obtained from large carps only if silver carp would not be stocked, and consume the rest with the family.     

Effects of all‐male,mixed‐sex and all‐female freshwater prawn in polyculture with major carps and molas in the fallow rice fields

This study was conducted to evaluate the effects of all‐male, mixed‐sex and all‐female freshwater prawn (Macrobrachium rosenbergii) in a polyculture with major carps (Catla catla and Labeo rohita) and self‐recruiting small fish molas (Amblypharyngodon mola) in the fallow rice fields of Bangladesh. There were three treatments with three replicates. All ponds were stocked with carps and molas plus either all‐male prawns (treatment MP), mixed‐sex prawns (MFP) or all‐female prawns (FP). Prawn, mola, catla and rohu were stocked 20 000, 20 000, 1750 and 750 ha^?1, respectively, in all treatments. The prawns were fed twice daily, starting at 8% body weight and gradually reduced to 3% body weight. The fish were fed in the morning with mustard oil cake and rice bran (1:2 ratios) at 3% body weight. Significantly higher production of prawns (697 kg ha^?1) was obtained in treatment MP, which yielded 34.7% and 56.2% more production than MFP and FP respectively. Significantly higher total production of 1620 kg ha^?1 and a higher benefit–cost ratio of 2.10:1 were also obtained in treatment MP. It can be concluded that an all‐male prawn culture is economically more viable than all‐female and mixed‐sex prawn cultures, along with other fish like major carps and the nutrient‐dense molas in the polyculture.     

Growth and production performance of threatened snakehead fish,Channa striatus (Bloch), at different stocking densities in earthen ponds

Production trials of threatened snakehead fish (Channa striatus) were carried out under different stocking densities in earthen ponds of Bangladesh. The average weight and length of the fingerlings during stocking was 17.63 ± 1.23 g and 13.21 ± 0.52 cm. Fingerlings were stocked at 5000 ha^?1 in treatment‐1 (T₁), 6250 ha^?1 in treatment‐2 (T₂) and 7500 ha^?1 in treatment‐3 (T₃) respectively. Fish in all the experimental ponds were fed with supplementary feed comprising of fish meal (30%) and mustard oilcake (70%) at the rate of 3–6% of estimated body weight two times per day. In addition, trash fish were supplied at the rate of 2–3% of the estimated biomass on each alternate day. In situ water quality parameters of the pond were within the suitable range for fish culture. The growth and survival of fingerlings were significantly higher in T₁ than in T₂ and T₃. The food conversion ratio was significantly lower (P<0.05) in T₁ than in T₂ and T₃. The estimated gross and net production of fish was higher in T₁, followed by T₂ and T₃. Overall, the highest growth, survival and production were obtained from T₁. Therefore, it could be concluded that of 5000 fingerlings ha^?1 is the most suitable stocking density for culturing C. striatus under a monoculture system in the earthen ponds for better production.     

Culture-based fisheries in non-perennial reservoirs in Sri Lanka: production and relative performance of stocked species

Abstract In Sri Lanka, there is a great potential for the development of culture-based fisheries because of the availability of around 12 000 non-perennial reservoirs in the dry zone (<187 cm annual rainfall) of the island. These reservoirs fill during the north-east monsoonal period in October to December and almost completely dry up during August to October. As these non-perennial reservoirs are highly productive, hatchery-reared fish fingerlings can be stocked to develop culture-based fisheries during the water retention period of 7–9 months. The present study was conducted in 32 non-perennial reservoirs in five administrative districts in Sri Lanka. These reservoirs were stocked with fingerlings of Indian (catla Catla catla Hamilton and rohu Labeo rohita Hamilton) and Chinese (bighead carp Aristichthys nobilis Richardson) major carps, common carp Cyprinus carpio L., genetically improved farmed tilapia (GIFT) strain of Nile tilapia, Oreochromis niloticus (L.) and post-larvae of giant freshwater prawn, Macrobrachium rosenbergii De Man, at three different species combinations and overall stocking densities (SD) ranging from 218 to 3902 fingerlings ha⁻¹, during the 2002–2003 culture cycle. Of the 32 reservoirs stocked, reliable data on harvest were obtained from 25 reservoirs. Fish yield ranged from 53 to 1801 kg ha⁻¹ and the yields of non-perennial reservoirs in southern region were significantly (P < 0.05) higher than those in the northern region. Naturally-recruited snakehead species contributed the catches in northern reservoirs. Fish yield was curvilinearly related to reservoir area (P < 0.05), and a negative second order relationship was evident between SD and yield (P < 0.05). Chlorophyll-a and fish yield exhibited a positive second order relationship (P < 0.01). Bighead carp yield impacted positively on the total yield (P < 0.05), whereas snakehead yield impact was negative. Bighead carp, common carp and rohu appear suitable for poly-culture in non-perennial reservoirs. GIFT strain O. niloticus had the lowest specific growth rate among stocked species and freshwater prawn had a low return.     

Effects of Stocking Size and Density of Tilapia on Macrobrachium rosenbergii in Polyculture

Studies were conducted to determine the effect of stocking size and density of prawns in polyculture.
In one experiment, postlarval prawns (av. wt. 0.02 g) were stocked in six 0.02 ha earthen ponds at 35,00O/ha. Two ponds were stocked with tilapia fry (av. wt. 0.14 g) and two were stocked with tilapia fingerlings (av. wt. 30.1 g), each at 10,000/ha. Two control ponds had no tilapia. Tilipia stocking size had no effect on prawn growth. Mean weight of prawns after 70 days of culture ranged from a low of 4.5 g when cultured with tilapia fingerlings to a high of 6.6 when cultured in monoculture. Prawn survival was adversely affected by tilapia fry. Average prawn survival in tilapia fry ponds was 65% compared to 75% and 91%, respectively, in tilapia fingerling and monoculture ponds.
In a second experiment, postlarval prawns were stocked in nine 0.02 ha earthen ponds at 40,000/ ha. Six ponds were stocked with 30 g tilapia fingerlings, three at 5,000/ha and three at 15,000/ha. Three control ponds received prawns only. After 100 days of culture, prawn weight ranged from an average of 15.9 g in monoculture ponds to 11.5 g in polyculture ponds. Survival was highest (93.8%) in low density polyculture ponds. Survival was lowest (85.6%) in prawn monoculture ponds. Tilapia reproduction had a negative impact on shrimp production.     

POLYCULTURE OF THE FRESHWATER PRAWN (Macrobrachium rosenbergii) WITH TWO COMBINATIONS OF CARPS IN MANURED PONDS

A study was conducted to 1) evaluate the compatibility of prawns (Macrobrachiurn rosenbergii) with carps, especially the effect of the common carp (Cyprinus carpio); and 2) measure the ability of prawns to utilize the foods available in manured systems. Carps used were the silver (Hypophthalmichthys molitrix), bighead (Aristichthys nobilis), grass (Ctenopharyngodon idella) and common carp (Cyprinus carpio). Four ponds (0.09 to 0.17 ha) were stocked with silver, bighead and grass carps while common carp were stocked in only two ponds. Total fish densities were 8,600/ha where four carps were stocked, but only 6,200/ha when common carp were omitted. Post-larval prawns (wt 0.116 g) were stocked at densities of 17/m². Swine (approximately 60/ha of pond surface area) were housed on pond dikes so that fresh manure continuously entered each pond. Two lots of swine were fattened during the experimental period and loadings of swine manure were calculated based on hog size and feed consumption. Growth periods were 163 days for fish and 107 and 121 days for separate stockings of prawns. Gains in biomass by prawns averaged 714 kg/ha in ponds without common carp and 364 kg/ha in ponds containing common carp. Gains in biomass for both fish and prawns were 3,619 kg/ha (19.8 kg/ha/day) in ponds with common carp and 2,924 kg/ha (18.0 kg/ha/day) in those without common carp. Prawn survival was higher (X = 84.5% vs X = 72.5%), but final average weight of prawns was lower (2.64 vs 5.86 g) in the presence of common carp due to competition for food between common carp and prawns. Competition from carp is believed to have exerted less influence on prawn survival than predation on small prawns by larger, faster-growing prawns.     

Stocking density effects on growth and production of the threatened silurid catfish,Mystus cavasius (Hamilton) fingerlings in nursery ponds

The fingerling‐rearing experiment of the threatened catfish, Mystus cavasius was carried out at different stocking densities in earthen nursery ponds. Twelve‐day‐old fry were stocked at 200 000 ha^?1 in treatment‐1 (T₁), 250 000 ha^?1 in treatment‐2 (T₂) and 300 000 ha^?1 in treatment‐3 (T₃) respectively. The mean length and weight of fry at stocking was 1.24 ± 0.25 cm and 0.11 ± 0.04 g respectively. Fry in all the experimental ponds were supplemented with SABINCO nursery feed for the first 14 days and starter‐I feed for days 15–56. The physico‐chemical parameters and plankton population of pond water were within the suitable level for fish culture. Growth in terms of final weight, final length, weight gain, length gain and specific growth rate and survival of fingerlings were significantly higher in T₁ than those in T₂ and T₃. Feed conversion rate was significantly lower in T₁ followed by T₂ and T₃ in that order. Significantly higher number of fingerlings was produced in T₃ than that in T₂ and T₁. Even then, consistently higher net benefits were obtained from T₁ than those from T₃ and T₂. Among the treatments evaluated, 200 000 fry ha^?1 was the best stocking density considering the highest growth, production and net benefits of fingerlings of M. cavasius in nursery ponds.     

Effects of Fertilization and of Fry Stocking Density on Pond Production of Fingerling Walleye,Stizostedion vitreum

The influence of fertilization and of fry stocking density on production of fingering walleye, Stizostedion vitreum, was evaluated in earthen ponds at North Platte State Fish Hatchery, North Platte, Nebraska. In 1990, five 0.4-ha ponds were fertilized with alfalfa pellets, and five were fertilized with soybean meal; four unfertilized ponds served as controls. All ponds were stocked with D2 (Dl = the day at hatch) walleye fry at 250.000ha. Differences in yield, number of fingerlings harvested, mean length, and mean weight amone treatments were not statistically significant (P> 0.05). In 691, two fertilization schedules (no fertilizer and fertilization with alfalfa pellets) and two fry stocking rates (250.000 and 375,000 fry/ha) were evaluated. Four ponds were used for each treatment. Statistically significant treatment differences were found in yield, number of fingerlings harvested/ha, average length, and average weight. Yield was higher in fertilized ponds compared with yield from unfertilized ponds at both stocking densities, but yield did not differ significantly between stocking density treatments given the same fertilizer treatment. Survival did not differ between density treatments, but total number of fish harvested was significantly greater from ponds stocked at the higher density. Fingerlings with the largest average weight were raised in fertilized ponds that were stocked at 250,00O/ha, while the smallest fingerlings were from unfertilized ponds that were stocked at 375,000ka. Days in culture interval, which varied among ponds by 9 days in 1990 and 10 days in 1991, was significantly correlated with most production variables in 1990 and with all production variables in 1991. Means of water quality variables were not significantly different between fertilized and unfertilized ponds in either year, but significant differences were found in means of three water quality variables between 1990 and 1991. Yield in both fertilized and unfertilized ponds in 1991 was less than in 1990.