Growth and physiological changes in scaled carp and blue tilapia under behavioral stress in mono- and polyculture rearing using a recirculated water system

Growth performance, carcass composition, liver and blood parameters ofscaled carp (C), Cyprinus carpio, and blue tilapia (T),Oreochromis aureus, reared for eight weeks in twomonoculture (100%C and 100%T) and two polyculture (60%C–40%T and40%C-60%T) conditions were investigated. In polyculture 40%C–60%T bothspecies achieved the highest levels of specific growth rate and the lowestlevels of food conversion ratio and carcass lipid content. In addition, theyexhibited the highest values of plasma pO₂ and pH and the lowestvalues of plasma pCO₂, cholesterol and albumin, although thedifferences among treatments were not significant in the case of tilapia.Tilapia showed significantly lower plasma Cl^– levels than underthe other conditions. Carp in monoculture and tilapia in polyculture60%C–40%T had the lowest levels of specific growth rate and significantlyhigher levels of liver lipids and plasma triglycerides than in the other groups.In addition, carp in monoculture exhibited a significantly higher haematocritthan in polyculture. No significant variations among treatments were observedconcerning plasma cortisol, glucose, osmolality, Na⁺, K⁺,HCO₃ ^– andHCO₃ ^–/H₂CO₃ in either species.The combination of scaled carp and blue tilapia, in which blue tilapia were themain species, proved to be the best for both species. It was suggested thatgrowth and physiological changes under mono- and polyculture rearing, in anintensive system, seem to be as a result of a different state of stress relatedto fish behavior.     

Evaluation of the production potential of Macrobrachium rosenbergii (de Man) in monoculture and in polyculture with Nile tilapia and common carp in Saudi Arabia

The feasibility of polyculture of Macrobrachium rosenbergii (de Man) with two fish species, Nile tilapia, Oreochromis niloticus (L.), and common carp, Cyprinus carpio L., was examined and compared with monoculture of M. rosenbergii in 100-m² ponds. Overall percentage of females (56.8%) was higher than that of males (43.2%). The proportions of females, males and their morphotypes did not differ significantly between monoculture and polyculture. After 196 days of culture, the mean harvest weight of prawns in monoculture (30.2 g) was significantly greater than that in polyculture (21.3 g). Yield in monoculture (1152 kg ha^-1) was significantly greater than (1.62 times) that of polyculture (711 kg ha^-1). Total yield from polyculture including yield of tilapia (2544 kg ha^-1) and common carp (2999 kg ha^-1) was almost five times as great as that of prawn monoculture. Survival and food conversion rate of M. rosenbergii did not differ significantly between monoculture and polyculture.     

Comparison of Tilapia Monoculture and Carp Polyculture in Fertilized Earthen Ponds

A comparison of a monoculture of Nile tilapia Oreochromis niloticus and a polyculture of carps (silver carp Hypophthalmichthys molitrix; rohu Labeo rohita; and mrigal Cirrhinus mriga la; ratio 4:3:3) was carried out in 200-m² earthen ponds fertilized with cattle manure and supplemented with inorganic fertilizer at 3-kg nitrogen and 1.5-kg phosphorus/ha per day. A control treatment of a tilapia monoculture without fertilizer inputs was included to assess the effect of pond basal fertility. Net yields of 23.5 kg/pond per 112 d (3.8 t/ha per 1 yr) in the tilapia monoculture and 19.2 kg/pond per 112 d (3.1 t/ha per yr) in the carp polyculture were not significantly different; net yields from unfertilized tilapia monoculture ponds were negative. In the carp polyculture, silver carp was the dominant species at harvest contributing 73% of the total net fish production compared to 9% and 19% by rohu and mrigal, respectively. Water quality data suggested that tilapia yields could have been further improved by increasing fertilization rate but that critical dissolved oxygen concentration constrained this option for carp polyculture.     

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.     

Effects of common carp (Cyprinus carpio Linnaeus, 1758) and the African catfish (Clarias gariepinus Burchell, 1822) on growth and reproductive performance of native tilapia Oreochromis shiranus (Boulenger, 1896)

A study was conducted to assess the effects of common carp and the African catfish on growth and reproduction of the native tilapia Oreochromis shiranus in Malawi. The study was done from 1 May to 1 October 2018 at the National Aquaculture Centre (NAC), Zomba. Four triplicated treatments were used: O. shiranus + carp (T1), O. shiranus + catfish (T2), O. shiranus + carp + catfish polyculture (T3) and O. shiranus monoculture (T4). Fish were stocked at uniform density of 0.8 fish/m². Data collection was done once every month. Results showed that O. shiranus mean weight gain (%), specific growth rate (% body weight/day), average daily gain (g fish^?1 day^?1) and condition factor (g/cm³) were highest in T3 and lowest in T1 and T4 treatments. T3 had better water quality regime and higher tilapia biomass than T1 and T4 treatments. Tilapia fry production (no. fry pond^?1 day^?1) was highest in T4 but did not significantly differ (p > .05) between T2 and T3 treatments. It is concluded that the farming of common carp in aquatic ecosystems containing the African catfish may not adversely affect growth and reproduction of O. shiranus and that the polyculture of the African catfish, common carp and tilapia can be adopted to mitigate the potential adverse effects of carp on the environment and improve tilapia growth.     

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.     

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.     

Effect of stocking density on growth,production and economic benefits of mixed sex Nile tilapia (Oreochromis niloticus) and African sharptooth catfish (Clarias gariepinus) in polyculture and monoculture

On‐farm fish production experiments were conducted for 240 days to investigate the effect of stocking density on growth, yield and economic benefits of Nile tilapia (Oreochromis niloticus) in monoculture and polyculture with African sharptooth catfish (Clarias gariepinus). Low stocking density (LSD), medium stocking density (MSD) and high stocking density (HSD) of 30 000, 60 000 and 90 000 fish ha^?1 respectively, were tested. O. niloticus cultured in polyculture attained significantly higher mean weight gain than those cultured in monoculture. O. niloticus and C. gariepinus raised together in polyculture attained significantly higher net annual yield than O. niloticus cultured alone in monoculture. Profitability analysis using partial enterprise budgets revealed that polyculture is a more profitable system than monoculture. The highest growth, yield and economic benefits were achieved at HSD and MSD than at LSD with no significant difference between HSD and MSD. Results demonstrate that farmers can achieve the highest net yield and economic benefits by culturing O. niloticus and C. gariepinus in polyculture at HSD and MSD, preferably MSD for economic reasons.     

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.     

鱼蚌混养对池塘水质、藻相结构及三角帆蚌生长的影响

2012年4月26日—2012年12月12日通过在鲢鳙鱼养殖池塘中放养不同密度的三角帆蚌,研究不同三角帆蚌放养比例对鲢鳙鱼养殖池塘中水质、藻相结构及三角帆蚌生长的影响。实验中,鲢鳙放养比例统一为3∶7,总密度为1.5尾/m3。三角帆蚌放养密度则设置4个水平,分别为单养鲢鳙鱼池塘(0只/m3),低密度三角帆蚌混养池塘(0.8只/m3),中密度三角帆蚌混养池塘(1.0只/m3)和高密度三角帆蚌混养池塘(1.2只/m3)。结果显示,混养三角帆蚌池塘的水化指标(TP、PO4-P、NH3-N、NO2-N和NO3-N)均显著低于单养鱼池塘。中密度三角帆蚌混养池塘除NH3-N和化学需氧量(COD)与低密度三角帆蚌混养池塘无显著差异外,其他各项水化指标均显著低于其他3个池塘,并且极显著低于单养鲢鳙鱼池塘。单养鲢鳙鱼池塘藻类平均密度均极显著高于鱼蚌混养池塘,其中在鱼蚌混养池塘中浮游植物密度与三角帆蚌密度成负相关关系。单养鲢鳙鱼池塘的浮游植物生物量均极显著低于中、高密度鱼蚌混养池塘,并且显著低于低密度混养池塘。浮游植物生物量与三角帆蚌密度成正相关关系,鱼蚌池塘中绿藻和裸藻的生物量在养殖过程中上升显著。低、中密度三角帆蚌混养池塘三角帆蚌存活率均显著高于高密度三角帆蚌混养池塘;低密度混养池塘中蚌湿重、壳长及壳宽相对增长率均为最大,显著高于中、高密度三角帆蚌混养池塘。研究表明,养鱼池塘混养三角帆蚌不仅能改善养殖池塘的水质,还能控制藻类数量,促使绿藻和裸藻等大型藻类的生长,提高养殖水体浮游植物的生物量总量,最终还能有效提高三角帆蚌的存活率及生长率。从改善水质,藻相结构,蚌成活率及生长等指标角度考虑,在鲢鳙鱼养殖池塘中,三角帆蚌最佳放养密度为1.0只/m3。     

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 stocking density of freshwater prawn Macrobrachium rosenbergii and addition of different levels of tilapia Oreochromis niloticus on production in C/N controlled periphyton based system

An on-station trial was conducted to evaluate the effect of stocking density of freshwater prawn and addition of different levels of tilapia on production in carbon/nitrogen (C/N) controlled periphyton based system. The experiment had a 2 × 3 factorial design, in which two levels of prawn stocking density (2 and 3 juveniles m^? 2) were investigated in 40 m² earthen ponds with three levels of tilapia density (0, 0.5 and 1 juveniles m^? 2). A locally formulated and prepared feed containing 30% crude protein with C/N ratio close to 10 was applied considering the body weight of prawn only. Additionally, tapioca starch was applied to the water column in all ponds to increase C/N ratio from 10 (as in feed) to 20. Increasing stocking density of tilapia decreased the chlorophyll a concentration in water and total nitrogen in sediment, and increased the bottom dissolved oxygen. The concentrations of inorganic nitrogenous species (NH₃–N, NO₂–N and NO₃–N) were low due to maintaining a high C/N ratio (20) in all treatment ponds. Increasing prawn density decreased periphyton biomass (dry matter, ash free dry matter, chlorophyll a) by 3–6% whereas tilapia produced a much stronger effect. Increasing stocking density of freshwater prawn increased the total heterotrophic bacterial (THB) load of water and sediment whereas tilapia addition decreased the THB load of periphyton. Both increasing densities of prawn and tilapia increased the value of FCR. Increasing prawn density increased gross and net prawn production (independent of tilapia density). Adding 0.5 tilapia m^? 2 on average reduced prawn production by 12–13%, and tilapia addition at 1 individual m^? 2 produced a further 5% reduction (independent of prawn density). The net yield of tilapia was similar between 0.5 and 1 tilapia m^? 2 treatments and increased by 8.5% with increasing stocking density of prawn. The combined net yield increased significantly with increasing stocking density of prawn and tilapia addition. The significantly highest benefit cost ratio (BCR) was observed in 0.5 tilapia m^? 2 treatment but freshwater prawn density had no effect on it. Therefore, both stocking densities (2 and 3 juveniles m^? 2) of prawn with the addition of 0.5 tilapia m^? 2 resulted in higher fish production, good environmental condition and economic return and hence, polyculture of prawn and tilapia in C/N controlled periphyton based system is a promising options for ecological and sustainable aquaculture.     

Comparison of food selection and growth performance of koi carp, Cyprinus carpio L., and goldfish, Carassius auratus (L.) in mono- and polyculture rearing in tropical ponds

To compare the effect of polyculture against conventional monoculture on ornamental carp production, investigations on food selection and growth performance of koi carp (K), Cyprinus carpio L. and goldfish (G), Carassius auratus (L.) were conducted in a 11‐week rearing experiment in two monoculture (100% K and 100% G) and five polyculture (90% K–10% G, 70% K–30% G, 50% K–50% G, 30% K–70% G and 10% K–90% G) conditions in tropical ponds. There were three replicates for each treatment. Environmental conditions and food availability were similar in all the treatments. Ivlev's electivity index showed that both fish species avoided phytoplankton and preferred cladocerans to other zooplankton groups (copepods and rotifers) in monotypic conditions. However, in the polyculture treatments, the positive electivity of goldfish towards cladocerans reduced significantly (P<0.05), while the percentage of copepods, rotifers and phytoplankton in the gut content increased. No significant differences in weight gain, specific growth rate and deformities were recorded at harvest for koi carp between the different treatments (P>0.05). Even the survival rate of koi carp recorded above 90% in all the treatments. However, the goldfish recorded significantly better weight gain, specific growth rate and survival in monoculture (100% G), compared with the polyculture treatments (P<0.05). Goldfish deformities were lowest (P<0.05) in the monoculture treatment (2.42%). The number of marketable fish above a set size limit of 4 g total weight was significantly higher in the two monoculture treatments, compared with the five polyculture treatments (P<0.05). Keeping in view of the dietary similarities of koi carp and goldfish, and the aggressive nature of koi carp in polyculture, it is suggested to refrain from polyculture of goldfish and koi carp until further documentations relating to optimum stocking density and management of polyculture of ornamental carps are available.     

Growth, Survival, Yield, and Size Distributions of Freshwater Prawn Macrobrachium rosenbergii and Tilapia Oreochromis niloticus in Polyculture and Monoculture Systems in Puerto Rico

Abstract.— Tilapia and freshwater prawn production in Puerto Rico for monoculture and polyculture systems were compared. The experiment consisted of three treatments with three replicates each. The stocking rates for the prawn monoculture, fish monoculture and polyculture treatments were respectively: 7 prawns/m², 1 tilapia/M², and 7 prawns with 1 tilapia/ m². The mean stocking size for tilapia and prawn were respectively, 7–8 g and 1–1.3 g. After 145 d of culture, yields and mean weight of tilapia in monoculture and polyculture system were not significantly different. Total yields were 2,942 and 2,769 kg/ha, respectively. Mean weights were 348 g in monoculture and 331 g in polyculture. Yields and mean weight of prawns in monoculture and polyculture were significantly different. Total yields were 1,367 and 951 kg/ha, respectively. Mean weights were 55 g in monoculture and 31 g in polyculture. Total yield in polyculture was 3,720 kg/ha showing an increase over the production separately obtained in prawn and fish monoculture.     

Introduction of jundia Rhamdia quelen (Quoy & Gaimard) and Nile tilapia Oreochromis niloticus (Linnaeus) increases the productivity of carp polyculture in southern Brazil

Fish polyculture is based on the assumption that each species has its own feeding niche and may increase the maximum standing crop of a pond by exploring a wider range of available food and ecological niches. In order to identify the better species ratio and to introduce jundia (JN) (Rhamdia quelen Quoy & Gaimard) and Nile tilapia (NT) (Oreochromis niloticus Linnaeus) in to the carp polyculture practiced in South Brazil, a 162‐day experiment was conducted, in 12 250‐m² earthen ponds (1.2 m deep). Treatment I (T‐I) contained 35% common carp, Cyprinus carpio (L.) (CC); 35% grass carp, Ctenopharyngodon idella Valenciennes (GC); 15% silver carp, Hypophthalmichthys molitrix Valenciennes (SC); and 15% bighead carp, Aristichthys nobilis Richardson (BC). Treatment II (T‐II) consisted of three ponds stocked at the following ratio: 17.5% CC, 35% GC, 15% SC, 15% BC and 17.5% JN. Treatment III (T‐III) consisted of three ponds with 35% CC, 35% GC, 7.5% SC, 7.5% BC and 15% NT. Treatment IV (T‐IV) consisted of three ponds with 17.5% CC, 35% GC, 7.5% SC, 7.5% BC%, 17.5% JN and 15% NT. No significant correlation was found between the treatments with different species ratio and water quality parameters. The final weight of different species, in different treatments, was statistically different. The major result was the clear positive effect on growth parameters observed by the introduction of JN and/or NT in to the carp polyculture. The yield per hectare was 2083.33±183 kg ha^?1 for polyculture with carp species; 2476.67±139.88 kg ha^?1 following the introduction of JN only; 2801.67±111.42 kg ha^?1 for isolated introduction of NT; and 2506.67±422.31 kg ha^?1 for simultaneous introduction of JN and NT. The introduction of JN and/or NT had a positive effect on growth parameters when compared with carp‐only polyculture. The reduction in CC ratio also had a positive effect on growth parameters.     

Biotic communities and feeding habits of Litopenaeus vannamei (Boone 1931) and Litopenaeus stylirostris (Stimpson 1974) in monoculture and polyculture semi-intensive ponds

Zooplankton, macrozoobenthos and feeding habits of Litopenaeus stylirostris and L. vannamei in monoculture and polyculture semi‐intensive experimental ponds were evaluated. Zooplankton was more abundant in monoculture of L. stylirostris (1002±670 organisms (org.) L^?1) than in monoculture of L. vannamei (470±37 org. L^?1), and polyculture (321±188 org. L^?1). The main zooplanktonic groups were polychaeta larvae, nauplii, copepods and polychaeta. Macrozoobenthos was more abundant in polyculture (6898±11 137 org. m^?2) compared with monoculture of L. stylirostris (3201±350 org. m^?2) and L. vannamei (2384±3752 org. m^?2). The main benthic groups were copepods, polychaeta, ostracods, nematodes and insects. Differences in feeding habits were found between species and regimes. Litopenaeus vannamei showed to be a more voracious species and fed mostly on organic detritus and benthos in both culture regimes. Litopenaeus stylirostris had a more restricted sources of feed in the ponds. The major component in the stomach content of both species was detritus. Macroalgae, sand, exuvia, formulated feed, prey and microalgae were minor components for both species (<7%). Ingestion of formulated feed was <4% for L. stylirostris and was not detected for L. vannamei. The stomach repletion rates were larger for L. vannamei (55.6% and 48.8%) than for L. stylirostris (43.75% and 44.89%). Litopenaeus stylirostris grew better in polyculture (10.3±3.4 g) that in monoculture (9.0±3.8 g). Litopenaeus vannamei grew better in monoculture (16.1±4.8 g) than in polyculture (13.4±4.5 g). For both species, feed conversion ratio was lower in polyculture.     

Recruitment control and production of Tilapia aurea (Steindachner) with the predator,Cichlasoma managuense (Günther)

The effects of different stocking rates and ratios of Tilapia aurea (Steindachner) in combination with Cichlasoma managuense (Günther) on tilapia recruitment and production were evaluated in 440 m² ponds. The research was conducted at the National Fisheries Station in El Salvador, Central America.The tilapia A_T value, the total weight of marketable tilapia (14 cm or larger) expressed as a percentage of the total weight of the whole tilapia population, averaged 96 or greater at a stocking ratio of 4:1 (fingerling tilapia: fingerling C. managuense) and at a stocking ratio of 8:1 (fingerling tilapia: adult C. managuense). Tilapia A_T values at a stocking ratio of 8:1 (fingerling tilapia: fingerling C. managuense) ranged from 71–89.Highest estimated annual production of marketable tilapia (3611 kg ha^?1) occurred at the highest stocking rate of 12000 tilapia ha^?1 in populations with an average tilapia A_T value of 98. Greatest weight gain of marketable tilapia (167 g of 1.17 g day^?1) occurred at the lowest stocking rate of 6000 tilapia ha^?1 in populations with an average tilapia A_T value of 99.Estimated annual production of marketable C. managuense ranged from 212–414 kg ha^?1. The average weight gain of marketable fish varied from 48–60 g (0.32–0.40 g day^?1). The average C. managuense, A_T value was 54, ranging from 29–84.The estimated production of marketable fish of both species at stocking rates of 6000, 9000 and 12000 tilapia ha^?1 in populations with tilapia A_T values of 96 or greater averaged 3295, 3290 and 4025 kg ha^?1 per year, respectively.     

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.     

Effect of supplemental dietary zinc sources on the growth and carbohydrate utilization of tilapia Smith 1840, Oreochromis niloticus × Oreochromis aureus

An 8‐week feeding trial was conducted to investigate the effect of supplemental dietary zinc sources on the growth performance and carbohydrate utilization of juvenile tilapia Smith 1840, Oreochromis niloticus × O. aureus. The goal was to compare the bioavailability of two zinc sources, zinc sulphate (ZnSO₄) or zinc methionine (ZnMet), by using two practical basal diets with 350 g kg^?1 (C350) or 400 g kg^?1 (C400) carbohydrates based on wheat as the carbohydrate source. The results showed that fish fed with a diet supplemented with 60 mg kg^?1 Zn from either ZnSO₄ or ZnMet had a significantly (P < 0.05) greater specific growth rate and protein efficiency ratio than those fed with the diets of ≤30 mg kg^?1 Zn. The composition of tilapia carcass was also found to be influenced by various levels of dietary zinc from the two zinc sources. The G6P‐DH in fish fed with the 20 mg kg^?1 ZnMet diet and the PK levels in fish fed with 20 mg kg^?1 ZnSO₄ and 30 mg kg^?1 ZnMet diet were significantly (P < 0.05) higher than those in fish fed with the C400 diet. The data suggest that supplemental dietary zinc from either ZnMet or ZnSO₄ significantly affects the growth performance and carbohydrate utilization of tilapia.