Effect of stocking density on growth performance,survival, production,and financial benefits of African sharptooth catfish (Clarias gariepinus) monoculture in earthen ponds

ABSTRACT

The present on-farm study assessed the effect of different stocking densities on growth, production, and financial benefits of African sharptooth catfish (Clarias gariepinus) in earthen ponds for 180 days. Low stocking density (LSD), medium stocking density (MSD), and high stocking density (HSD) of 3, 6, and 9 fish m^?2, respectively, were tested. C. gariepinus stocked at LSD and MSD showed significantly higher weight gain, specific growth rate, and final mean weight than those cultured at HSD (P < .05). There was a significant linear relationship between the stocking density and the yields and financial variables (P < .05). Net fish yields were significantly higher for C. gariepinus reared at HSD and MSD than those stocked at LSD (P < .05). Similarly, C. gariepinus raised at MSD and HSD generated significantly more profit than those cultured at LSD (P < .05). Results demonstrated that farmers can achieve high net yield and financial benefits by stocking C. gariepinus at HSD of 9 fish m^?2.     

Effects of stocking density on mortality,growth and physiology of juvenile Amur sturgeon (Acipenser schrenckii)

To evaluate effects of stocking density on welfare of Amur sturgeon (Acipenser schrenckii), an experiment was designed using three initial stocking densities in flow‐through tanks (LSD = 3.7 kg m^?3, MSD = 6.9 kg m^?3, and HSD = 9.3 kg m^?3, respectively) for 60 days. Growth, body composition, and haematological and biochemical parameters were monitored. The mortality and feed conversion rate (FCR) were not affected by stocking density. However, the specific growth rate (SGR), final weight and weight gain in the HSD group were significantly lower than in the LSD and MSD groups. The hepatosomatic (HSI) and viscerosomatic indices (VSI) varied inversely with regard to stocking density. Stocking density did not affect crude protein levels in fish. In contrast, the total lipid level was significantly higher in the LSD group compared to the MSD and HSD groups. The levels of erythrocytes and haemoglobin were positively correlated with stocking density. Serum total bilirubin and urea in HSD group were significantly higher than in the LSD group while serum triglycerides showed opposite tendencies. Differences between treatments were not registered for glucose, total protein and albumin. In conclusion, higher stocking density resulted in increased immunosuppression and enhanced energy mobilization. The latter was necessary to enable Amur sturgeon to cope with crowding.     

Effects of stocking density on growth performance and welfare‐related physiological parameters of Atlantic salmon Salmo salar L. in recirculating aquaculture system

Stocking density, representing a potential source of long‐term stress, is widely recognized as a critical factor in aquaculture husbandry. Atlantic salmon were reared at low‐density (LSD, ~9.80–18.41 kg m^?3, initial to final density), medium‐density (MSD, ~19.62–36.96 kg m^?3) and high‐density (HSD, ~28.79–53.54 kg m^?3) stocking levels for 66 days to investigate the stress‐induced changes in fish growth and welfare. At the end of the trial, the salmon in HSD group showed significant lower final weight and higher ration level than those in MSD and LSD groups (P < 0.05). The salmon farmed in LSD group had higher special growth rate (SGR) and lower feed conversion ratio (FCR) (P < 0.05). However, stocking density could not affect the mortality, condition factor and coefficient of variation of salmon. The pectoral fin index of salmon in LSD group was significantly higher than that in HSD group (P < 0.05). Fifteen haematological and serum parameters were detected to assess the stress and welfare levels of salmon. The salmon farmed in HSD group had higher glucose (GLU) level and lower Cl^?, haemoglobin (HGB) and red blood cell (RBC) concentrations (P < 0.05). Contrast to the pattern of superoxide dismutase (SOD) activity, the cortisol, maleic dialdehyde (MDA) and alkaline phosphatase (ALP) levels of HSD group were higher than those in other two groups (P < 0.05). All these findings will provide a reference for selecting suitable stocking density in Atlantic salmon farming industry.     

Growth,digestive enzymes activities,serum biochemical parameters and antioxidant status of juvenile genetically improved farmed tilapia (Oreochromis niloticus) reared at different stocking densities in in‐pond raceway recirculating culture system

The feeding trial was conducted in 80 days to assess the effects of stoking densities on growth, digestive enzymes activities, serum biochemical parameters and antioxidant status of juvenile genetically improved farmed tilapia (GIFT, Oreochromis niloticus) reared in in‐pond raceway recirculating culture system (IPRS). Fish (initial body weight: 6.25 ± 0.32g ) were randomly allotted to six in‐pond raceways (22 × 5 × 2.5 m) stocked at three different stocking densities: low stocking density (LSD, 0.28 kg/m³), medium stocking density (MSD, 0.57kg /m³) and high stocking density (HSD, 0.85 kg /m³). The results indicated that no significant differences were observed in final body weight, weight gain and specific growth rate of GIFT reared at different stocking densities on day 20 (p > 0.05). Fish reared in the HSD group showed poor growth than those reared in the LSD and MSD groups on day 50, but fish reared in the MSD and HSD groups showed poor growth than those reared in the LSD group on day 80. There were no significant differences found in digestive enzyme activities, serum cortisol, lysozyme and superoxide dismutase (SOD) content, hepatic catalase (CAT), total SOD, total antioxidant capacity (T‐AOC) activities and malondialdehyde (MDA) content among fish reared at different densities treatments (p > 0.05). Fish reared in the HSD group exhibited significant higher red blood cell number, haematocrit and glucose (GLU) contents on day 80 (p < 0.05). In brief, under this trial conditions, high stocking densities (0.57 kg/m³) resulted in decrease in growth, and GIFT might have an adaptation capability to crowding stress without a change in antioxidant activity, some physiological and immune parameters.     

崇明清水蟹与澳洲红螯螯虾高效生态混养技术

为抵御单一养殖崇明清水蟹带来的风险,开展了崇明清水蟹与澳洲红螯螯虾高效生态混养试验。以2020年上海崇东水产养殖专业合作社的混养试验为例,养殖池塘面积1 hm~2,蟹种放养量12 000只,产量1 125 kg,澳洲红螯螯虾放养量15 000尾,产量450 kg,总产值31.5万元,利润20.1万元。结果表明,采用崇明清水蟹与澳洲红螯螯虾高效生态混养模式,不会影响清水蟹的产量,且单位面积利润比单养模式提高了34%,因此是1种生态效益和经济效益兼顾的养殖模式。     

Production of the Malawi chambo, Oreochromis karongae (Trewavas, 1941) association, and Oreochromis shiranus (Boulenger, 1896) in polyculture with the African catfish, Clarias gariepinus (Burchell, 1822)

Results are reported of the growth and yield of the Malawi chambo, Oreochromis karongae (Trewavas, 1941) association, and Oreochromis shiranus (Boulenger. 1896) in polyculture with Clarias gariepinus (Burchell. 1822). Six ponds of 150 m² were assigned to two replicates of three treatments: C. gariepinus and O. shiranus; C. gariepinus and chambo spawned on station; C. gariepinus and chambo collected from the lake. Total fish stocking density was 3 m^?2, and stocking ratio 1:2 (C. gariepinus: titapias). Initial mean body weights were 10.9 g for O. shiranus. 13.2 g for C. gariepinus and 13.3 g for chambo. The ponds were fertilized with chicken manure at the rate of 13.5 kg dry matter ha^?1 day^?1, representing the daily NPK loading of 0.618.0.186 and 0.191 kg ha^?1, respectively. Maize bran was applied at 3% body weight day^?1 for 168 days. Fish growth rate for C. gariepinus was significantly higher (P < 0.05) than that of the tilapias. Weight gains were 0.48-0.57 g day^?1 for C. gariepinus, 0.30-0.31 g day^?1 for chambo and 0.24 g day^?1 for O shiranus. There was no difference (P > 0.05) in the growth of chambo despite the source of fingerlings. More fish biomass came from C. gariepinus stocked at 1 m^?2 than from the tilapias stocked at 2 m^?2. Extrapolated fish yields in the range of 4.37-4.75 t ha^?1 year^?1 were obtained from the polyculture of chambo and C. gariepinus. Oreochromis shiranus and C. gariepinus gave 3.95 t ha^?1 year^?1. Low water temperatures for 112 days slowed the growth of tilapias but did not seem to inhibit the growth of C. gariepinus. Chicken manure and maize bran, applied at smallholder farmer's level, has produced higher yields than by using O. shiranus in monoculture at optimal temperatures. The yields obtained show that the polyculture system is feasible during the cold season and may justify investment in aquaculture at semi-intensive level in Malawi.     

The potential of mixed culture of genetically improved farmed tilapia (Oreochromis niloticus) and freshwater giant prawn (Macrobrachium rosenbergii) in periphyton-based systems

The production performance of genetically improved farmed tilapia (GIFT, Oreochromis niloticus) and freshwater prawn (Macrobrachium rosenbergii) in periphyton‐based systems were studied in farmers' ponds at Mymensingh, Bangladesh. Fifteen ponds (200–300 m² area and 1.0–1.5 m in depth) were used to compare five stocking ratios in triplicate: 100% GIFT, 75% GIFT plus 25% prawn, 50% GIFT plus 50% prawn, 25% GIFT plus 75% prawn and 100% prawn. Ponds were stocked at a total density of 20 000 GIFT and/or prawn ha^?1. Bamboo poles (mean diameter 6.2 cm and 5.5 pole m^?2) were posted in pond bottoms vertically as periphyton substrate. Periphyton biomass in terms of dry matter (DM), ash‐free DM and chlorophyll a were significantly higher in ponds stocked with prawn alone than in ponds with different combinations of GIFT and prawn. Survival of GIFT was significantly lower in ponds stocked with 100% GIFT (monoculture) whereas, that of prawn was significantly higher in its monoculture ponds indicating detrimental effects of GIFT on prawn's survival. Individual weight gains for both species were significantly higher in polyculture than in monoculture. The highest total fish and prawn yield (1623 kg GIFT and 30 kg prawn ha^?1) over 125–140 days culture period was recorded in ponds with 75% GIFT and 25% prawn followed by 100% GIFT alone (1549 kg ha^?1), 50% GIFT plus 50% prawn (1114 kg GIFT and 68 kg prawn ha^?1), 25% GIFT plus 75% prawn (574 kg GIFT and 129 kg prawn ha^?1) and 100% prawn alone (157 kg ha^?1). This combination also gave the highest economic return. Therefore, a stocking ratio of 75% GIFT plus 25% prawn at a total density of 20 000 ha^?1 appeared to be the best stocking ratio in terms of fish production as well as economics for a periphyton‐based polyculture system.     

Influence of Stocking Density on Growth and Physiological Responses of Beluga,Huso huso (Brandt, 1869), and Ship Sturgeon,Acipenser nudiventris (Lovetsky, 1828), Juveniles in a Flow‐through System

The influence of three different initial stocking densities (low stocking density [LSD] = 1.5 kg/m²; medium stocking density [MSD] = 3 kg/m²; and high stocking density [HSD] = 6 kg/m²) in flow‐through systems was evaluated on growth and welfare in beluga, Huso huso, and ship sturgeon, Acipenser nudiventris, juveniles for 2 mo. Fish were kept in 18 concrete square tanks (2.0 × 1.0 × 1.2 m³) at 22.3 ± 0.4 C and under a natural photoperiod. In both species, the growth performance in terms of final body weight, weight gain, specific growth rate, and feed intake significantly decreased with increasing stocking density (P < 0.05). In both species, the percent of neutrophils increased after 60 d of trial (P < 0.05). Moreover, hematocrit and white blood cell counts increased after 60 d of trial in ship sturgeon (P < 0.05). Plasma immunoglobulin significantly decreased with increasing stocking density in both species. Plasma insulin‐like growth factor I decreased with increasing stocking density in beluga; however, it was not affected in ship sturgeon. Overall, these results showed that the LSD group in both species demonstrated more homogeneous and higher growth rate than the MSD and HSD groups.     

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.     

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.     

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.     

High stocking density induces crowding stress and affects amino acid metabolism in Senegalese sole Solea senegalensis (Kaup 1858) juveniles

Fish held at high stocking densities are generally exposed to chronic stress situations that impose severe energy demands and may predispose the fish to infection. Senegalese sole Solea senegalensis (Kaup) juveniles (78.8±18.9 g body weight) were maintained at low (LSD; 4 kg m^?2 at the end of the experiment), medium (MSD; 9 kg m^?2) and high (HSD; 14 kg m^?2) stocking densities during a period of 63 days. Although disease outbreaks were observed in fish reared at HSD, growth and food consumption did not vary among different treatments. Results from plasma cortisol and free amino acids (FAAs) showed significant differences among different rearing densities pointing to HSD as stressful rearing condition. However, higher plasma glucose and osmolality levels indicated that fish held at MSD may also be under stress. The higher usage of FAAs from the HSD group may be due to the higher demand for energy production in order to cope with stressful rearing conditions, higher rate of protein synthesis or due to synthesis of other important metabolites related to stress response. Therefore, results from the present study point out to HSD as a stressful rearing condition and suggest that crowding stress may affect amino acid requirements.     

Protocols for the development of indigenous species: polyculture of indigenous species under Malawian smallholder conditions*

Shire tilapia, Oreochromis shiranus shiranus (Boulenger 1897), was grown in monoculture and polyculture with either straightfin barb, Barbus paludinosus (Peters 1852), or threespot barb, Barhus trimaculatus (Peters 1852), (collectively known as matemba) under conditions which simulated smallholder farming conditions in Southern Malawi. Over 150 days, B. paludinosus-O. shiranus shiranus polyculture was significantly (P < 0.05) more productive than either O. shiranus shiranus or B. paludinosus monoculture. Over 107 days. B. trimaculatus-O. shiranus shiranus monocultures and polyculture were equally productive (P < 0.05). Average weights of O. shiranus shiranus and matemba were not affected by polyculture (P < 0.05). Survival of O. shiranus shiranus from stocking to harvest was not affected by polyculture with B. paludinosus, but was significantly (P < 0.05) lower in polyculture with B. trimaculatus. Survival of matemba from stocking to harvest was not affected by polyculture (P<0.05). Total weight and number of O. shiranus shiranus and B. paludinosus juveniles produced during growout were the same in monoculture and polyculture (P<0.05). but total weight of B. trimaculatus was significantly (P<0.05) lower in polyculture. Polycultures were clearly more profitable than all monocultures. Next most profitable were tilapia monocultures. Matemba monocultures were least profitable. Based on these findings, preliminary protocols for the development of other indigenous fish species for aquaculture are described.     

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.     

Stocking density affects growth and metabolic parameters in the brill (Scophthalmus rhombus)

In this work, the effects of the stocking density on the physiological stress and biometric features of the brill were studied. No differences for survival rate, feeding efficiency, Conversion Index and feeding intake were not detected among the treatments. The growth rate showed an inverse lineal relationship with stocking density, and there were no significant differences between specimens cultured at medium and high density. Plasma cortisol and osmolality were directly related to stocking density, though the former was not significantly different among the treatments. Plasma glucose and lactate significantly increased, while stocking density rose. Triglycerides enhanced significantly in MSD and HSD with respect to LSD cultured specimens. Differences among treatments were not registered for hepatic glucose, triglycerides and amino acids. However, glycogen showed an inverse lineal relationship with respect to stocking density with significant differences between low and high stocking density. Several lipid classes were different among the treatments, with the high-density specimens presenting the highest values. Liver total lipid was not significantly different among the treatments, but total polar lipid was higher in high density. Muscle metabolites did not vary significantly among the treatments. Concluding, the brill showed a clear secondary response to crowding stress through the mobilization of energy substrates to tissues, evoking a reduction in the growth and other biometric parameters.     

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.     

Enhancing productivity of Labeo victorianus ponds using maize flour as a carbohydrate source

This study investigated the effects of manipulating carbon–nitrogen (C/N) ratio and fish stocking density on pond productivity: total heterotrophic bacteria counts, plankton biovolume and benthic macro‐invertebrates. Labeo victorianus juveniles were reared for 72 days in 18 hapas suspended in six ponds measuring 150 m² at densities of 10, 15 and 25 fish m^?2. Fish in hapas received a locally formulated and prepared feed containing 295 g kg^?1 crude protein, and ponds were treated with a C/N ratio of either 10 or 20. All treatments were carried out in triplicate. Increasing C/N ratio from 10 to 20 increased phytoplankton by 13% and zooplankton biovolume by 25% in the water column (P < 0.001). Total benthic macro‐invertebrates biovolumes were also 30% higher (P < 0.05) with a C/N ratio of 20 compared to 10. Total heterotrophic bacteria counts increased both in water and sediment by 29% while net yield increased by 15% from 1534 (C/N 10) to 1821 (C/N 20) kg ha^?1 72 day^?1. C/N ratio of 20 and a stocking density of 25 fish m^?2 led to the highest yield, survival, production and net benefits. It is suggested that polyculture may lead to better utilization of pond communities to further improve pond productivity.     

Effects of C/N ratio and periphyton substrates on pond ecology and production performance in giant freshwater prawn Macrobrachium rosenbergii (De Man, 1879) and tilapia Oreochromis niloticus (Linnaeus, 1758) polyculture system

The production performances of giant freshwater prawn Macrobrachium rosenbergii and Nile tilapia Oreochromis niloticus in C/N‐controlled periphyton‐based polyculture systems were evaluated in triplicate. Three different management practices were compared: the traditional practice without addition of periphyton substrates and carbohydrate (Control), addition of maize flour to maintain a carbon: nitrogen rate of 20:1 (treatment CN) and addition of both maize flour and periphyton substrates (treatment CN+P). This experiment used a pre‐optimized stocking density of tilapia and freshwater prawn by Asaduzzaman et al. Aquaculture [286 (2009) 72]. All ponds were stocked with prawn (3 m²) and monosex Nile tilapia (1 m^?2). Bamboo side shoots were posted vertically into the pond bottoms as periphyton substrate covering an additional area of 171 m² for periphyton development. A locally formulated and prepared feed containing 17% crude protein with C/N ratio close to 15:1 was applied twice daily in all ponds considering the body weight of freshwater prawn only. Water quality parameters, except total alkalinity did not vary significantly (P > 0.05) among treatments. Both, organic matter and total heterotrophic bacterial loads (THB) in the sediment were significantly (P < 0.05) higher in treatment CN+P followed by treatment CN and control. Periphyton biomass in terms of dry matter and chlorophyll a values constantly decreased during the culture period. Substrates contributed 66% and 102% higher net yield of freshwater prawn than CN and control treatment respectively.     

Effect of stocking density on the growth performance and yield of Nile tilapia [Oreochromis niloticus (L., 1758)] in a cage culture system in Lake Kuriftu,Ethiopia

This research was conducted to investigate the effect of stocking density on the growth performance and yield of Oreochromis niloticus in cage culture in Lake Kuriftu. The treatments had stocking densities of 50 (50F), 100 (100F), 150 (150F), and 200 (200F) fish per m^?3. All treatments were in duplicate. Juveniles with an average weight of 45. 76±0.25 g were stocked in the treatments. The fish were fed a composite mixture of mill sweeping, cotton seed, and Bora food complex at 2% of their body weight twice per day using feeding trays for 150 days in powdered form. The growth performance of O. niloticus was density dependent. The final mean weight of O. niloticus ranged 147.76±0.28–219.71±1.42 g and the mean daily weight gain was 0.69±0.01–1.15±0.02 g day^?1. Fish held in cages with lower density were heavier than the ones held at higher densities, and showed higher weight gain and daily weight gain. The most effective stocking density, in terms of growth parameters, was 50 fish m^?3. The gross yield (4.5–20.55 kg cage^?1) showed a significant difference with increasing stocking density (P<0.05). Moreover, the apparent food conversion ratio (2.48–7.22) was significantly affected by stocking density (P<0.05). However, survival rate was not affected by stocking density (P>0.05). It can be concluded that the most effective stocking densities were at 50 fish m^?3 cage for larger size fish demand in a short period and 200 fish m^?3 for higher gross production with supplementary feed.     

Comparison of the survival, growth and yield of red swamp crayfish and white river crayfish in monoculture and polyculture systems

Red swamp crayfish (Procambarus clarkii) and white river crayfish (P. acutus acutus) production for monoculture and polyculture systems were compared. The experiment consisted of three treatments with six replicates each. The stocking rates were 43 crayfish/m² in 0.18-m² tanks fitted with a stand of green rice. Each tank contained six crayfish, either six individuals of the same species or three individuals of each species. The mean stocking size for monoculture and polyculture were 32.6 ± 0.05 and 33.0 ± 0.07 mm total length, respectively. Survival and growth was assessed at 30-day intervals over a 90-day experimental period. Survival of two species was the same in the monoculture system (62.5%). Survival of P. clarkii in the polyculture system (25.0%) was significantly lower than in the monoculture system (62.5%), whereas P. acutus acutus survived at similar rate in the polyculture system (41.7%) and monoculture system (62.5%). Survival was lower but growth was higher in the polyculture system than in the monoculture system for both species. Growth of P. acutus acutus in the polyculture system was significantly greater than in the monoculture system. No difference was observed in the growth of P. clarkii between polyculture and monoculture and the overall growth of P. acutus acutus and P. clarkii was similar for the 90 days. Yield did not differ significantly between monoculture and polyculture systems (P < 0.05). Total yields were in 1.15 kg/ha in monoculture and 1.18 kg/ha in polyculture.