Nursing duration and pond fertilization level affect polycultures of Indian major carp (rohu Labeo rohita and mrigal Cirrhina mrigala) with monosex Nile tilapia Oreochromis niloticus

This study investigated the effects of nursing duration on the subsequent performance of rohu (R) Labeo rohita and mrigal (M) Cirrhina mrigala in polyculture with monosex male Nile tilapia (T) Oreochromis niloticus at four levels of pond fertilization. Nile tilapia, rohu and mrigal were stocked at a ratio of 4:1:1 in a 90‐day trial based on 40 20‐m² pens fixed in four 400‐m² earthen ponds. Growth of carp fingerlings during prolonged nursing (5 or 12 months) was stunted compared with fish nursed over a conventional duration of 3 months (3) but showed superior growth subsequently. Mean daily weight gain of stunted rohu (12) ranged from 2.2 to 2.8 g per fish day^?1 compared with 1.1–1.6 g per fish day^?1 for younger fish (3). The comparable ranges for mrigal were 1.9–2.8 and 1.4–2.1 g per fish day^?1. Growth of Nile tilapia was inversely related to duration of carp nursing at the four levels of fertilization. Nile tilapia showed more response to increasing levels of fertilizer input (Y=?1.421+1.716X, where Y is the daily weight gain of Nile tilapia and X is the fertilizer level, r²=0.98, P<0.01, n=12). At a high level of fertilization (3.0 kg N:1.5 kg P ha^?1 day^?1), performance of stunted fingerlings (5 and 12) of both rohu and mrigal was similar (range 2.3–2.8 g per fish day^?1, P>0.05), but younger mrigal (M3) grew faster than rohu (2.1 g per fish day^?1 and 1.6 g per fish day^?1 respectively). Older rohu (12) appeared to perform particularly well, and Nile tilapia poorly at the lowest level of fertilization (1.5 N:0.75 kg P ha^?1 day^?1), suggesting the impact of age of seed on competition within polycultures. The net fish yield (NFY) of tilapia was not affected significantly (P>0.05) by differential stocking age of carps; therefore, combined NFY of the three experimental fish species was not affected by the age of carp, as tilapia was the dominant species in polyculture. The highest combined NFY of all species in the most intensively fertilized pond (3.0 N:1.5 P kg ha^?1 day^?1) was calculated at 4.06±0.08 g·m^?2 day^?1, which was significantly higher (P<0.001) than the yield (1.82±0.12 g·m^?2 day^?1) from the pond with the lowest fertilization. At the highest fertilizer level, tilapia, rohu and mrigal contributed 72%, 14% and 14%, respectively, to the NFY, whereas the ratio was 60%, 20% and 20% at the lowest fertilization level. The study indicated that yields from tilapia in polyculture with the two carp species in more eutrophic water can be optimized if advanced nursing of carps is practised. Moreover, higher inputs of inorganic fertilizer and advanced nursing of carp are economically attractive under Bangladeshi conditions. Advanced nursing of rohu also improves its performance in more extensive systems when tilapia densities are high.     

Cage‐pond integration of African catfish (Clarias gariepinus) and Nile tilapia (Oreochromis niloticus) with carps

Cage‐pond integration system is a new model for enhancing productivity of pond aquaculture system. A field trial was conducted using African catfish (Clarias gariepinus) and Nile tilapia (Oreochromis niloticus) in cages and carps in earthen ponds. There were four treatments replicated five times: (1) carps in ponds without cage, (2) tilapia at 30 fish m^?3 in cage and carps in open pond, (3) catfish at 100 fish m^?3 in cage and carps in open pond, (4) tilapia and catfish at 30 and 100 fish m^?3, respectively, in separate cages and carps in open pond. The carps were stocked at 1 fish m^?2. The cage occupied about 3% of the pond area. The caged tilapia and catfish were fed and the control ponds were fertilized. Results showed that the combined extrapolated net yield was significantly higher (P < 0.05) in the catfish, tilapia and carps integration system (9.4 ± 1.6 t ha^?1 year^?1) than in the carp polyculture (3.3 ± 0.7 t ha^?1 year^?1). The net return from the tilapia and carps (6860 US$ ha^?1 year^?1) and catfish, tilapia and carps integration systems (6668 US$ ha^?1 year^?1) was significantly higher than in the carp polyculture (1709 US$ ha^?1 year^?1) (P < 0.05). This experiment demonstrated that the cage‐pond integration of African catfish and Nile tilapia with carps is the best technology to increase production; whereas integration of tilapia and carp for profitability.     

Effects of feeding rates on growth and production of Nile tilapia, common carp and silver carp polycultured in fertilized ponds

Abstract In an attempt to identify appropriate feeding rates for multispecies of fish raised in fertilized earthen ponds, the present work was conducted over a 19‐week experimental period to establish the growth performance, production and body composition of Nile tilapia, common carp and silver carp fed 0.0%, 0.5%, 1.0%, 3.0%, 5.0% biomass and to apparent satiation (treatments). Twelve ponds were stocked with a similar number and weight of each fish species. Two ponds were assigned to each of the treatments, and a 25% protein pelleted fish feed was used to feed fish at the specified rate of feeding. At the end of the experiment, growth, weight gain, survival, yield and body composition of fish groups were affected by the treatments. The economic effectiveness also varied among treatments. The most conspicuous attribute of the feeding rates was its lack of influence on growth (g day^?1), weight gain (g per fish), yield (kg ha^?1) or body composition of silver carp. The results of whole‐body proximate analysis indicated that various feeding rates had either an irregular pattern or no effects on the protein and ash gain per 100 g of fish body weight (bw) gain. The most notable exceptions were significant (P < 0.05) increases in body fat and gross energy gains in Nile tilapia, common carp and silver carp accompanied by decreases in percentages of moisture (but not in silver carp) as feeding rate increased. Among the six different feeding levels, feeding to apparent satiation (feed amount was equivalent to 2.67% of fish bw day^?1) appeared to be optimal, as it significantly (P < 0.05) supported the highest fish production, income and net profit compared with all other treatments except for the 3% feeding level, for which the differences in those measurements were comparable.     

Effects of stocking density on production and economics of Nile tilapia (Oreochromis niloticus) and freshwater prawn (Macrobrachium rosenbergii) polyculture in periphyton-based systems

The present research investigated the effect of stocking density on pond (75 m², depth 1.2 m) production of Nile tilapia (Oreochromis niloticus) and freshwater prawn (Macrobrachium rosenbergii) stocked at a fixed 3:1 tilapia:prawn ratio. Three stocking densities were tried in triplicate: 20 000 ha⁻¹ (treatment TP‐20), 30 000 ha⁻¹ (TP‐30) and 40 000 ha⁻¹ (TP‐40). The ponds were provided with bamboo as substrate for periphyton development. Bamboo poles (mean diameter 5.5 cm and 5.0 poles m⁻²) were posted vertically into pond bottoms, resulting in 60% additional substrate area in each pond. On average, 43 genera of algae and 17 genera of zooplankton were identified from pond water, whereas 42 genera of algae and six genera of microfauna were attached to bamboo substrates. No differences were observed between treatments in the ash‐free dry matter (AFDM), chlorophyll a and phaeophytin a content of periphyton (P>0.05). Survival of tilapia and prawn and individual weight gain of tilapia were lower (P<0.05) in treatment TP‐40. The net yields were higher (P<0.05) in treatments TP‐30 (2209 and 163 kg ha⁻¹ 105 day⁻¹ of tilapia and prawn respectively) and TP‐40 (2162 and 141 kg ha⁻¹ of tilapia and prawn respectively) than in treatment TP‐20 (1505 and 136 kg ha⁻¹ of tilapia and prawn respectively). The net tilapia yields were quadratic correlated (R²=0.92) with fish stocking density. The cost–benefit analysis shows that the net profit margin was highest in treatment TP‐30 (69%), followed by TP‐20 (50%) and TP‐40 (44%).     

Effects of common carp Cyprinus carpio (L.) and feed addition in rohu Labeo rohita (Hamilton) ponds on nutrient partitioning among fish, plankton and benthos

The effects of introducing common carp (CC) and of adding artificial feed to fertilized rohu ponds on water quality and nutrient accumulation efficiency were studied. All ponds were stocked with 15 000 rohu ha^?1. Treatments included ponds with rohu alone, rohu plus 5000 common carp ha^?1 and rohu plus 10 000 CC ha^?1. A comparison was also made between supplementally fed and non‐fed ponds. The overall highest nitrogen (N) and phosphorus (P) concentrations were observed in ponds with 5000 CC ha^?1, followed by ponds with 10 000 and 0 CC ha^?1. The largest fractions of N and P inputs accumulating in fish, phytoplankton and zooplankton were observed in ponds with 5000 CC ha^?1, followed by ponds with 10 000 CC ha^?1 and subsequently ponds without CC. Relatively more nutrients accumulated in benthic organisms in ponds without than in ponds with CC. A smaller fraction of the nutrient input was retained in fish, plankton and benthic organisms in ponds without CC compared with ponds with CC. Compared with 5000 CC ha^?1, stocking 10 000 CC ha^?1 can be considered as overstocking, because this leads to lower fish production and relatively less nutrients retained in plankton and benthic organisms.     

Effects of stocking density on growth, yield and profitability of farming Nile tilapia, Oreochromis niloticus L., fed Azolla diet, in earthen ponds

Two consecutive experiments were conducted to study the effects of stocking density on growth, food utilization, production and farming profitability of Nile tilapia (Oreochromis niloticus) fingerlings (initial mean weight: 16.2 ± 0.2 g) fed Azolla, as a main component in diet. In experiment 1, fish were hand‐fed twice daily with three isonitrogenous (28.5% crude protein) and isocaloric (14.5 kJ g⁻¹) diets A30, A35 and A40 containing 30%, 35% and 40%Azolla, respectively, for 90 days. Diets were formulated by mixing Azolla with locally available by‐products. No significant differences were found in growth parameters and production (P>0.05). Total investment cost was significantly higher with A30 (P<0.05), but same profitability values were obtained with all diets (P>0.05). In experiment 2, three stocking densities, 1, 3 and 5 m⁻², were assigned to three treatments T₁, T₂ and T₃ respectively. Fish were hand‐fed twice daily with diet A40. The final mean weight (89.53–115.12 g), the mean weight gain (0.81–1.10 g day⁻¹), the specific growth rate (1.90–2.20% day⁻¹) and the apparent food conversion ratio (1.29–1.58) were affected by stocking density, with significant difference (P<0.05) at 5 m⁻², compared with the other densities. Stocking density did not affect survival rate (P>0.05). Yield and annual production increased with increasing stocking density, ranging from 7.10 ± 0.90 to 25.01 ± 1.84 kg are⁻¹ and 28.79 ± 3.66 to 101.42 ± 7.48 kg are⁻¹ year⁻¹, respectively, with significant differences between all densities (P<0.05). Higher stocking density resulted in higher gross return and lower cost of fish production, with significant variations (P<0.05). The net return increased with increasing stocking density (P<0.05). However, both densities of 3 and 5 m⁻² produced the same profitability values. On the basis of growth values and economic return, it was concluded that Nile tilapia could be raised at a density of 3 fish m⁻² with A40 to improve production and generate profit for nutritional security and poverty alleviation in rural areas.     

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.     

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.     

Polyculture of silver barb, Puntius gonionotus (Bleeker), Nile tilapia, Oreochromis niloticus (L.), and common carp, Cyprinus carpio L., in Vietnamese ricefields: feeding ecology and impact on rice and ricefield environment

Rice production, ricefield environment and the feeding ecology offish were studied in an experiment conducted at a rice-fish station in the Mekong Delta, Vietnam. In total, six treatments (three replicates) were investigated: four different polyculture combinations of small sized silver barb, Puntius gonionotus (Bleeker), Nile tilapia, Oreochromis niloticus (L.), and common carp, Cyprinuso carpio L.; one treatment with pre-grown fingerlings; and a control treatment in which no fish were stocked. No insecticides or fungicides were utilized before or during the experiment. Frequent fertilization of the water and a low rice plant biomass during the early vegetative growth phase stimulated the development of phytoplankton and zooplankton. The total weed biomass was low (maximum = 5.3 g dry weight m^?2) and not significantly (P < 0.05) different between the treatments. A major component of the silver barb diet consisted of rice plants and accessible grains. However, the introduction of silver barb only had a significant effect on the number of rice tillers in the ratoon crop and not on the paddy yield. The quantitative differences in the diets of tilapia and common carp were minimal: both species fed mostly on detritus. Ricefields without silver barb produced the highest paddy yield (3120 kg ha^?1). The total yield of introduced fish increased after increasing the stocking density of silver barb from 319.9 to 494.1 kg ha-¹. The highest fish yield (541.8 kg ha-1) was obtained by stocking pre-grown fingerlings in the ricefields.     

Effect of salinity on carrying capacity of adult Nile tilapia Oreochromis niloticus L. in recirculating systems

Effect of salinity on carrying capacity of a recirculation system for Nile tilapia, Oreochromis niloticus L.; production was assessed. Survival, growth and feed conversion ratio of adult Nile tilapia fed 30% crude protein diet for 88 days were measured at three different salinity levels (8, 15 and 25 g L^?1) and two stocking densities (20 and 40 m^?3) in three independent recirculating systems. Highest survival (98%) and a linear growth in net biomass (P<0.01) was observed in both densities at 8 g L^?1 and in 20 m^?3 treatment at 15 g L^?1. Highest net biomass growth was observed in the 40 m^?3 stocking density treatment at 8 g L^?1 salinity level (P<0.05). Overall biomass growth was significantly affected by salinity indicating a decrease in Nile tilapia carrying capacity with increased salinity. About 11 000 kg ha^?1 crop^?1 of Nile tilapia can be obtained in recirculating systems at 8 g L^?1 salinity, significantly higher than the net production at 15 g L^?1 (5200 kg ha^?1 crop^?1) and 22 g L^?1 (4425 kg ha^?1 crop^?1).     

The effect of the introduction of Nile tilapia (Oreochromis niloticus,L.) on small indigenous fish species (mola,Amblypharyngodon mola,Hamilton; chela,Chela cachius,Hamilton; punti,Puntius sophore,Hamilton)

This is the first controlled experiment to quantify the effect of introduced tilapia on indigenous species. This experiment was conducted in small earthen ponds (100 m²) to assess the impact of mixed‐sex or all‐male Nile tilapia (Oreochromis niloticus) on small indigenous species (SIS) commonly found in south Asia, mola (Amblypharyngodon mola), chela (Chela cachius) and punti (Puntius sophore). Ponds were fertilized, then stocked with 0.56 fish m^?2 of water surface area in the mixed‐sex and all‐male tilapia treatments and 0.42 fish m^?2 in the treatment without tilapia. No additional nutritional inputs were applied after stocking. Treatments were: mixed‐sex tilapia with SIS, mono‐sex male tilapia with SIS and SIS without tilapia (control). All treatments were stocked with 14 fish per species. All species reproduced during the 21‐month culture duration. The number of recruits varied by species, Tilapia reproduced in greater numbers than SIS. Tilapia numbers at harvest were the highest (451 ± 25/100 m²) in the mixed‐sex treatment compared with mola (221 ± 22/100 m²), chela (94 ± 8/100 m²) and punti (100 ± 7/100 m²). The number of mola was higher (399 ± 33/100 m²) in the all‐male tilapia treatment. There was reduction in the number of mola and chela in the treatment containing mixed‐sex tilapia. Gut content analysis combined with water sampling revealed that all fish species fed selectively. Significant interspecies dietary overlap was found between Nile tilapia and SIS and among SIS. Thus, there is potential for tilapia to compete with indigenous fish species when space and other resources are limiting, but a longer duration study with varying level of management is needed to determine how successfully tilapia competes with locally adapted SIS.     

Pond farming of Nile tilapia, Oreochromis niloticus (L.), in northern Cameroon. Adding hand-sexed male tilapia to graze the dense algal blooms in ponds with African catfish, Clarias gariepinus (Burchell)

Four earthen ponds (250 m² each) were stocked each with 250 small catfish (W₀=39g). In treatment A, African catfish. Clarias gariepinus (Burchell), were raised in monoculture, while in treatment B catfish were raised in polyculture with an additional 125 male Nile tilapia, Oreochromis niloticus (L.) (W₀=44g). Feeding of cottonseed cake was at about 4% of catfish body weight day^?1. Daily feed quantities, however, were averaged over all four ponds so that each pond received the same amount of cottonseed cake. Rearing time was 118 days. In treatment A, catfish grew to an average weight of 200g. In treatment B, catfish reached 158g and tilapia 185g, Extrapolated marketable fish production was strikingly similar in all four ponds (around 4.8 t ha^?1 year^?1). No synergistic effect was obtained by stocking microphagous tilapia, although the feeding of cottonseed cake enhanced dense algal blooms in all ponds. Catfish did not appear to exploit the tilapia recruits, as an indirect pathway of algae cropping.     

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 day and night on swimming,grazing and social behaviours of rohu Labeo rohita (Hamilton) and common carp Cyprinus carpio (L.) in simulated ponds

Diel rhythmicity of grazing, swimming, resting and social interactions of rohu (Labeo rohita) (weight 66.5–68.3 g) and common carp (Cyprinus carpio) (79.9–82.0 g) were observed in 1 m² simulated ponds using video images. Fish behaviour was monitored during a full 24‐h period, starting at 08:00 hours with a 15‐min recording, which was repeated every 3 h. Rohu spent more time grazing during the day than at night. Grazing activity peaked at the beginning and at the end of the day. Grazing and resting of rohu were negatively correlated. Common carp grazed day and night, showing no distinct grazing peak. Considering the grazing time of rohu and common carp, a feeding schedule with two feeding times at 07:30 and 16:30 hours might be appropriate for better food intake and conversion in rohu–common carp polyculture system.     

The impact of net-isolated polyculture of tilapia (<Emphasis Type="Italic">Oreochromis niloticus</Emphasis>) on plankton community in saline–alkaline pond of shrimp (<Emphasis Type="Italic">Penaeus vannamei</Emphasis>)

We used 12 land-based experimental enclosures (6 m × 5 m) in a saline–alkaline pond of shrimp (Penaeus vannamei) to determine the impact of net-isolated polyculture of tilapia (Oreochromis niloticus) on plankton communities for 40 days. Tilapias were stocked in net cages suspended in enclosures, in polyculture ponds including tilapia and shrimp. Four tilapia biomass were tested: 0, 39, 115 and 227 g m⁻². Shrimp stocking biomass were 0.7 g m⁻² in all treatments. There were three replicates in each treatment. Our results showed that the presence of tilapia significantly reduced phytoplankton biomass directly through predation and indirectly through top-down effect. The stocking of tilapia reduced zooplankton biomass, particularly rotifer biomass. However, copepod biomass was not been significantly affected. So, net-isolated polyculture of tilapia can thus have a strong impact on phytoplankton allowing the co-existence of large numbers of copepods with planktivorous fish and improving the water quality of shrimp ponds.     

Polyculture of silver barb, Puntius gonionotus (Bleeker), Nile tilapia, Oreochromis niloticus (L.), and common carp, Cyprinus carpio L., in Vietnamese ricefields: fish production parameters

The fish production parameters of five polyculture combinations, consisting of small and large silver barb, Puntius gonionotus (Bleeker), small and large Nile tilapia, Oreochromis niloticus (L.), and small common carp, Cyprinus carpio L., fingerlings in three replicates, were investigated in a rice-fish culture experiment (duration 149 days) conducted in the Mekong Delta, Vietnam. The survival rate was not significantly (P > 0.05) affected by the polyculture combination, but when grouped according to species, the mean survival of silver barb and tilapia was 64.3% and 63.7%, respectively, significantly higher than the mean common carp survival rate (33.4%). The growth of silver barb and tilapia was proportionally related to the stocking density, probably because of intraspecific competition and a synergistic interaction between silver barb and tilapia. The growth of common carp was not significantly different among the polyculture combinations. The highest net production (474.1 kg ha^?1) was obtained in the polyculture combination consisting of 80% small-sized silver barb fingerlings, but the fish was not marketable at that time. In concurrent rice-fish culture, it is recommended to raise large silver barb fingerlings. Small tilapia can be polycul-tured with silver barb, provided a stocking density lower than 1400 ha^?1. Common carp is considered less suitable because of a limited tolerance for the water quality conditions in the ricefield and the large size required by the market.     

Effects of Two Densities of Caged Monosex Nile Tilapia, Oreochromis niloticus, on Water Quality, Phytoplankton Populations, and Production When Polycultured with Macrobrachium rosenbergii in Temperate Ponds

The effects of different densities of caged Nile tilapia, Oreochromis niloticus, on water quality, phytoplankton populations, prawn, and total pond production were evaluated in freshwater prawn, Macrobrachium rosenbergii, production ponds. The experiment consisted of three treatments with three 0.04‐ha replicates each. All ponds were stocked with graded, nursed juvenile prawn (0.9 ± 0.6 g) at 69,000/ha. Control (CTL) ponds contained only prawns. Low‐density polyculture (LDP) ponds also contained two cages (1 m³; 100 fish/cage) of monosex male tilapia (115.6 ± 22 g), and high‐density polyculture (HDP) ponds had four cages. Total culture period was 106 d for tilapia and 114 d for prawn. Overall mean afternoon pH level was significantly lower (P ≤ 0.05) in polyculture ponds than in CTL ponds but did not differ (P > 0.05) between LDP and HDP. Phytoplankton biovolume was reduced in polyculture treatments. Tilapia in the LDP treatment had significantly higher (P ≤ 0.05) harvest weights than in the HDP treatment. Prawn weights were higher (P ≤ 0.05) in polyculture than prawn monoculture. These data indicate that a caged tilapia/freshwater prawn polyculture system may provide pH control while maximizing pond resources in temperate areas.     

The effect of stocking different ratios of common carp, Cyprinus carpio L., and tilapias in polyculture ponds on production characteristics and profitability

Production characteristics and profitability of three carp-tilapia stocking ratios (1:1, 1:2 and 1:5) were compared in a semi-intensive polyculture system. The. experiment was carried out at the same total stocking density of 1 fish m², in nine 1000-m² earthen ponds. Common carp, Cyprinus carpio L., and a tilapia hybrid, Oreochromis niloticus (L.) x 0. aureus (Steindachner), were stocked at a joint density of 900 fish per pond, while grass carp, Ctenopharyngodon idella (Cuvier & Valenciennes), and silver carp, Hypophthalmichthys molitrix (Valenciennes), were each stocked at 50 fish per pond in all treatments. Mean harvested weights of both common carp and the tilapia hybrid were markedly decreased upon the increase in density of their own species. Survival of all four species was over 80% in all three carp-tilapia stocking ratios. The differences in relative profitability of the three carp-tilapia stocking ratios did not exceed 10% on the basis of 1991 prices. However, based on 1994 prices, relative profitability of the 1:2, and particularly, the 1:5 carp-tilapia stocking ratio were 35% and 41% higher than the 1:1 ratio, respectively. This was because of the increase in the price of large carp and tilapia of all sizes, and a decreases in the price of small carp.     

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.     

Productivity and Economics of Nile Tilapia Oreochromis niloticus Cage Culture in South-East Brazil

ABSTRACT

Fish cage culture is an intensive, continuous-flow fish farming system, allowing intensive exploitation of water bodies with relatively low capital investment. This study aimed to determine the production function of Nile tilapia, Oreochromis niloticus, in cages; the profit-maximizing biomass at 300–400 and 500–600 fish per m³ for cages of different volumes; and the influence of water body conditions in fish performance. Feed intake, survival rate, and water temperature were monitored daily; dissolved oxygen, pH, and transparency of water were monitored each 15 days. Caged tilapia were fed daily on commercial, floating pellets (32% crude protein) at 0900, 1300, and 1700, and feeding rate was adjusted based on weight gain and survival rate. Data were analyzed statistically by ANOVA (P = 0.05) and regression analysis; the Mitscherlich function was chosen to represent the production function. Carrying capacity of both stocking densities reached 200 kg/m³ and no differences were found (P > 0.05) regarding accumulated biomass and individual average weight over time. The larger stocking density yielded larger accumulated biomass and had better feeding efficiency and no differences between individual average weights of fish at both densities were observed (P > 0.05). Profit-maximizing biomass at 500–600 fish/m³ was 145 kg/m³ and at 300–400 fish/m³ was 121 kg/m³. Cage farming of Nile tilapia at 500–600 fish/m³, individual average weight 283 g, presented many advantages: optimization of space and production time, better feed efficiency, higher fish production per unit volume of cages, and increased profitability.