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.     

A partial economic analysis for Nile tilapia Oreochromis niloticus L. and sharptoothed catfish Clarias gariepinus (Burchell 1822) polyculture in central Kenya

Aquaculture development in Kenya has been hampered by lack of targeted feeds. Chemical fertilizers can enhance natural food production and thus indirectly provide protein to complement energy-rich cereal brans used as feed. Consequently, an experiment was conducted at Sagana Fish Farm in central Kenya to realize least-cost combinations of rice bran and fertilizer. Twelve 800 m² (0.08 ha) ponds were stocked with juvenile (32 g) Oreochromis niloticus L. at 2 m⁻² and Clarias gariepinus (Burchell 1822) (fingerlings of 4.6 g) at 0.2 m⁻². Four treatments, calculated to approximate isonitrogenous conditions, were applied in triplicate as follows: (1) urea and diammonium phosphate (DAP) to provide 16 kg of N ha⁻¹ week⁻¹ and 4 kg of P ha⁻¹ week⁻¹; (2) urea and DAP applied to give 8 kg of N ha⁻¹ week⁻¹ and 2 kg of P ha⁻¹ week⁻¹, plus rice bran fed at 60 kg ha⁻¹ day⁻¹; (3) rice bran fed at 120 kg ha⁻¹ day⁻¹; (4) rice bran as in treatment 3 and fertilizer as in treatment 2. Ponds were sampled monthly to measure fish growth, and drained completely after 20 weeks. A partial economic analysis indicated minimal net profits of K.Sh. 18 851 (US$ 251), K.Sh. 9895 (US$ 132), K.Sh. 3299 (US$ 44) and K.Sh. 7015 (US$ 94) for treatments 1–4, respectively, because of high feed and seed costs.     

Inherent variation in growth efficiency of African catfish Clarias gariepinus (Burchell, 1822) juveniles

Understanding the major causes of growth variation is crucial for the success of fish farming since its reduction contributes to maximize production efficiency, reduce food waste and improve water quality. The growth variation observed in aquaculture has been associated with the establishment of social hierarchies. However, some studies suggest that this variation may not be mainly a consequence of social hierarchies but mainly a result of inherent (genetic) differences. This study investigates the magnitude of individual responses, independently of group effects (fish housed individually), in growth efficiency and feeding behaviour of African catfish Clarias gariepinus (Burchell 1822). Despite the low variation in initial body weight (6.5%) and cumulative feed consumption (7.5%) over the experimental period, catfish exhibited high variation in final body weight (18.1%), specific growth rate (17.2%) and feed conversion ratio (27.9%), suggesting that individual variation in growth efficiency is important in determining growth rate. This individual variation may be related with individual differences in protein/fat deposition since faster growing fish deposited more protein and less fat than slower growing fish. Pronounced individual differences in feeding behaviour (reaction towards feed and time spent eating) were also observed and correlated with individual differences in growth efficiency. Fast eaters were the fast growers. We suggest that the growth variation observed in African catfish may be inherent and that the use of grading to increase uniformity should be further investigated.     

丁香油对鲤鱼和罗非鱼的麻醉作用

本实验将丁香油按体积比加入水中制备成不同浓度梯度的麻醉剂,分别在不同水温下对两种大小规格的鲤鱼和罗非鱼进行麻醉试验.28℃水温时,随着丁香油浓度由0.05 mL·L-1到0.1mL·L-1、0.15mL·L-1增加,鲤鱼和罗非鱼麻醉时间均缩短.鲤鱼恢复时间增长,罗非鱼则缩短.在0.1mL·L-1浓度下,随着水温从21℃到24℃、26℃、28℃升高,鲤鱼和罗非鱼麻醉作用时间缩短.鲤鱼恢复时间增长而罗非鱼则缩短.28℃水温0.1mL·L-1浓度下,小鲤鱼麻醉时间比小罗非鱼短,而恢复时间比小罗非鱼长.结果显示,丁香油是一种高效、廉价的鱼类麻醉剂.     

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.     

Growth and health performance of African catfish Clarias gariepinus (Burchell 1822) juvenile fed with graded levels of biofloc meal

The objective of the study was to evaluate the utilization of biofloc meal as a feed ingredient in enhancing the growth and health status of African catfish (Clarias gariepinus) juvenile. The study consisted of two experiments, that is digestibility and growth experiments. The digestibility of two biofloc meals produced with two different carbon sources, that is tapioca and molasses, were assessed in the digestibility experiment. Whereas the effect of four dietary treatments with different levels of biofloc meal, that is 0%, 5%, 10% and 20%, on the fish growth performance, feed utilization, immuno‐haematological response, antioxidant status and robustness against environmental stress were evaluated in the growth experiment. The results showed that the digestibility of dry matter, protein, lipid and phosphorus of biofloc grown using molasses as the carbon source were remarkably higher than that grown using tapioca (p < 0.05). The inclusion of biofloc meal in the diets at 10% and 20% resulted in higher feed intake, fish growth and final biomass and protein efficiency ratio, and lower feed conversion ratio (p < 0.05). Furthermore, the red blood cells counts, phagocytic, lysozyme activities and antioxidative capacity were significantly enhanced in the fish provided with diet containing 20% biofloc meal (p < 0.05).The fish survival following salinity stress test was higher in the treatments with biofloc meal at 10% and 20% inclusion levels. In conclusion, dietary inclusion of biofloc meal could improve the growth performance and health status of African catfish juvenile and an inclusion level of 20% could be recommended.     

Optimal dietary carbohydrate to lipid ratio in African catfish Clarias gariepinus (Burchell 1822)

An 8-week feeding trial was conducted in a recycling water system at 28±1°C to investigate carbohydrate to lipid ratio (CHO:L ratio) in African catfish Clarias gariepinus (12.32±0.04g). Five isonitrogenous (40% crude protein) and isoenergetic (20kJg^–1 gross energy (GE)) fishmeal based diets with varying carbohydrate to lipid (CHO:L g/g) ratios of 0.74, 1.13, 1.66, 2.47 and 3.42 for diets 1–5, were tested, respectively. The diets containing a fixed protein to energy ratio (P:E ratio) of 20-mg proteinkJ^–1 GE were fed to triplicate groups of 20 fish (per 30-L tank). Fish were fed 5% of their body weight per day adjusted fortnightly. Diet 1, containing 14% carbohydrate and 21% lipids with a CHO:L ratio of 0.74 produced the poorest (P<0.05) growth rates, feed and protein efficiency. Increasing carbohydrate content in the diets to 27% concomitant with a reduction in lipid content to 16% with a CHO:L ration of 1.66 of diet 3 significantly improved (P<0.05) growth rates, feed and protein efficiency. A further increase in dietary carbohydrate up to 38% and a decrease in lipids levels to 11% with a CHO:L ratio ranging from 1.66 to 3.42 (diet 3 – 5) did not significantly improve the fish performance. Apparent net protein utilisation (ANPU) of fish fed diet 4 was higher (P<0.05) than for diets 1–3 but did not differ from diet 5. Higher lipid deposition (P<0.05) in whole body and liver were observed with decreasing dietary CHO:L ratios as increasing lipid levels. Whole body protein and liver glycogen content, digestive enzyme activities (protease and lipase) and histological examination of intestine and liver of fish fed varying CHO:L diets did not show any discernible changes among the dietary treatments. However intestinal -amylase activity increased (P<0.05) with increasing dietary carbohydrate levels. This study revealed that African catfish can perform equally well on diets containing carbohydrate ranging from 27 to 38% of the diet, with lipid content ranging from 16 to 11% or at CHO:Lg/g ratio of 1.7–3.4.     

In vivo activity of native GnRHs and their analogues on ovulation in the African catfish, Clarias gariepinus (Burchell)

Four distinct forms of native gonadotropin‐releasing hormone (GnRH) and two newly designed analogues were tested for their in vivo activity to induce ovulation in African catfish. The effects of these peptides on ovulatory parameters were compared with those of carp pituitary and [d ‐Ala⁶, Pro⁹‐NEt]‐mammalian GnRH analogue (mGnRHa), two tested ovulation‐inducing agents in African catfish. Assessment of ovulation was carried out by determining the ovulation ratio and the relative quantity of egg produced. From the results of the experiments, the order of potency of the native GnRH peptides is summarized as chicken GnRH‐II (cGnRH‐II) >salmon GnRH (sGnRH) >mammalian GnRH >chicken GnRH‐I (cGnRH‐I). Chicken GnRH‐II was as potent as mGnRHa while cGnRH‐I was totally ineffective. The new d ‐Orn⁶‐cGnRH‐II and d ‐Orn⁶‐sGnRH with a substitution at position 6 with d ‐isomer residue were as potent as the most extensively used mGnRHa, indicating that the position 6 modification might be more crucial than the substitution at the C‐terminal. On the basis of our results, the potential use and incorporation of cGnRH‐II and sGnRH for the development of more generic spawning induction therapies are suggested.     

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.     

Approaches to optimizing dietary protein to energy ratio for African catfish Clarias gariepinus (Burchell, 1822)

An 8‐week feeding trial was conducted in a recycling water system at 28 ± 1 °C to investigate protein to energy ratio (P/E ratio) in African catfish Clarias gariepinus (10.9 ± 0.04 g). Six fishmeal‐based diets of two protein levels (330 and 430 g kg^?1), each with three lipid levels (40, 80 and 120 g kg^?1) resulted in P/E ratios ranging from 15.5 to 21.3 mg protein kJ^?1 gross energy (GE) were fed to 20 fish (per 30‐L tank) in triplicate. Fish were fed 50 g kg^?1 of their body weight per day adjusted fortnightly. Significantly higher (P < 0.05) growth rates and feed conversion efficiency were evident in fish fed with higher protein diet. The highest growth rate was found by fish fed 430 g kg^?1 protein, 21.2 kJ^?1 GE with a P/E ratio of 20.5 mg protein kJ^?1 GE. Significantly indifferent (P > 0.05) values of protein utilization were found in‐between the both (higher and lower) protein diets. Higher lipid deposition (P < 0.05) in whole body and liver was observed with increasing dietary lipid level at each protein diet and as higher (P < 0.05) for the lower protein diets. Liver glycogen tended to decrease with increasing gross energy at each protein diet and higher protein diet showed comparatively lower values (P > 0.05). Digestive enzyme activities (protease and lipase) and histological examination of intestine and liver of fish fed varying P/E diets found no significant differences in response to experimental diets. The study reveals that African catfish C. gariepinus performed best the diet containing 430 g kg^?1, 21.2 kJ g^?1 and 20.5 mg protein kJ g^?1 GE protein, gross energy and P/E ratio, respectively.     

The impact of elevated water nitrite concentration on physiology,growth and feed intake of African catfish Clarias gariepinus (Burchell 1822)

The nitrite threshold concentration in rearing water of African catfish (Clarias gariepinus) was assessed. African catfish with an initial mean (SD) weight of 219.7 (57.8) g were exposed to an increasing range of water nitrite from 6 (Control) to 928 μM nitrite for 28 days. Mean (SD) plasma nitrite concentrations increased from 5.0 (3.6) to 32.5 (12.6) μM at 928 μM ambient nitrite. The increase in nitrite was accompanied by gradual increase in plasma nitrate from 41.6 (28.4) μM to 420.2 (106.4) μM. Haematocrit, haemoglobin, methemoglobin, plasma concentrations of cortisol, glucose, lactate, osmolality, gill morphology and branchial Na⁺/K⁺‐ATPase activity were not affected. Feed intake, final weight, SGR, FCR and mortality were not affected. We advise not to exceed a water nitrite concentration of 43 μM (0.6 mg L^?1 NO₂^?‐N) to prevent the risk of reduced growth and feed intake in African catfish aquaculture.     

Characterization of the testicular semen of the African catfish, Clarias gariepinus (Burchell, 1822), and its short-term storage

Semen of the African catfish, Clarias gariepinus (Burchell, 1822), was investigated with respect to its cellular composition, sperm cell density, maturation grade, motility and fertility. Storage conditions were tested, whereby sperm viability was assessed by measurement of the motility after activation and by fertility tests. Testicular semen differed in its composition, i.e. the sperm density and numbers of spermatids, according to the maturity grade of the testis. Two semen types could be distinguished: semen type I was characterized by high sperm densities and low numbers of spermatids and semen type II had lower sperm densities and higher numbers of spermatids. Two semen types did not differ in motility and fertility (when adjusted for differences in sperm density). During storage, the sperm viability was influenced by the sodium concentration of the storage medium, temperature, membrane stabilizers as bovine serum albumen (BSA) or hen egg yolk, antibiotics and oxygen. Semen viability was maintained best when it was diluted at a ratio of 1:5 in storage solution (150 mmol L^?1 NaCl, 2.5 mmol L^?1 KCl, 1 mmol L^?1 CaCl₂, 1 mmol L^?1 MgSO₄, 20 mmol L^?1 Tris (pH 8.5) and 0.5% BSA or 0.5% hen egg yolk) and stored at 4 °C. Oxygen gassing and addition of antibiotics (1 mg mL^?1 gentamycine sulphate) to the storage solution affected the two semen types in different ways. Antibiotics had no effect on type I semen, but had a positive effect on type II semen. Oxygen gassing had a positive effect on type I semen but a negative effect on type II semen.     

The influence of food particle size on gastric emptying and growth rates of fingerling African catfish, Clarias gariepinus Burchell, 1822

This study investigates the effect of feed particle size on gastric evacuation and growth of fingerling African catfish, Clarias gariepinus . Fish (0.97 ± 0.07 g) held in 40-cm diameter tanks at a stocking density of 5 fish L^–1 (25 fish per tank) were presented with one of four sizes of food particles (1, 1.5, 2 and 3 mm diameter). Gastric evacuation rate could be described by an exponential function with small feed particles being evacuated more rapidly: values of 0.076, 0.054, 0.047 and 0.029 were observed for fish fed 1 mm, 1.5 mm, 2 mm and 3 mm food particles, respectively. Growth rates were highest for fish fed the 1.5 and 2 mm pellets. Based on these findings, recommendations are made on the optimum food particle size for C. gariepinus fingerlings.     

The impact of elevated water nitrate concentration on physiology,growth and feed intake of African catfish Clarias gariepinus (Burchell 1822)

The nitrate threshold concentration in rearing water of African catfish (Clarias gariepinus) was assessed. Female African catfish with an initial mean (SD) weight of 154.3 (7.5) g were exposed to 0.4 (Control), 1.5, 4.2, 9.7 and 27.0 mM nitrate for 42 days. Mean (SD) plasma concentrations of nitrate increased from 71 (29) to 6623 (921) μM at the highest ambient nitrate level. Mean (SD) plasma nitrite concentration ranged from 1.2 (0.5) to 7.9 (9.0) μM. Haematocrit, plasma concentrations of non‐esterified fatty acids (NEFA), cortisol, glucose, lactate, osmolality, gill morphology and branchial Na⁺/K⁺‐ATPase activity were not affected. Feed intake and specific growth rate were significantly reduced at the highest nitrate concentration. We advise not to exceed a water nitrate concentration of 10 mM (140 mg L^?1 NO₃‐N) to prevent the risk of reduced growth and feed intake in African catfish aquaculture.     

Digestive capabilities of three commensal fish species: carp, Cyprinus carpio L., tilapia, Oreochromis aureus×O. niloticus, and African catfish, Clarias gariepinus (Burchell 1822)

Abstract. This paper examines the digestibility of different feed mixtures by three species of fish: carp, Cyprinus carpio L., tilapia, Oreochromis aureus × O. niloticus , and African catfish, Clarias gariepinus (Burchell 1822). Protein from poultry sources was digested better by tilapia than by carp or catfish, but no significant difference was found in the case of protein mainly from fish meal. Carp showed the best ability to digest fats, followed by catfish, with tilapia having the least ability. Tilapia digested carbohydrate better than the other two species, however, whether from wheat or corn sources. The same pattern applies to the digestibility of energy.     

Quality of testicular semen of the African catfish Clarias gariepinus (Burchell, 1822) and its relationship with fertilization and hatching success

Quality differences of testicular semen of the African catfish, Clarias gariepinus, and their influence on fertilization and hatching success were investigated. In accordance with an earlier study, two semen types of the African catfish were distinguished according to testicular maturity stage. Semen type I derived from males with white mature testes whereas type II semen derived from males with grey, partly mature testes. Semen volume, sperm cell concentration and seminal plasma pH was significantly higher in type I semen than in type II semen, while sperm motility was similar. Similar fertilization percentages were obtained with semen type I and semen type II. However, the hatching percentage was higher and the percentage of deformed hatched larvae was lower for type I semen. There were significant (P<0.01) positive correlations between sperm motility and fertilization percentage, seminal plasma pH and hatching percentage and a negative correlation between seminal plasma pH and percentage of deformed larvae. Therefore seminal plasma pH and sperm motility are useful to predict semen quality of the African catfish.     

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.     

The effect of nearly closed RAS on the feed intake and growth of Nile tilapia (Oreochromis niloticus), African catfish (Clarias gariepinus) and European eel (Anguilla anguilla)

One of the challenges that Recirculating Aquaculture Systems (RAS) are still facing is the risk that in RAS fish grow less than in flow-through systems due to the accumulation of substances originating from feed, fish or bacteria associated with the water re-use. The present study investigated whether RAS with high and low accumulation levels of these substances affect feed intake and growth of Nile tilapia Oreochromis niloticus, African catfish Clarias gariepinus, and European eel Anguilla Anguilla. One-hundred and twenty individuals of each species were used (start body weights: Nile tilapia 264.8 ± 8.3 g; African catfish 253.2 ± 2.1 g and European eel 66.6 ± 1.3 g). For a period of 39 days, growth and feed intake were compared between high and low accumulation RAS. HIGH accumulation RAS was designed for maximal accumulation of substances in the water by operating the system at nearly-closed conditions (30 L/kg feed/d), using mature biofilters and high feed loads; and (2) LOW accumulation RAS was designed to be a proxy for flow-through systems by operating at high water exchange rates (1500 L/kg feed/d), new biofilters and low feed load. HIGH accumulation RAS induced a reduction in feed intake (42%) and growth (83%) of Nile tilapia, as compared to systems that are a proxy for flow-through conditions. This effect was not observed in European eel and African catfish. The cause of this reduced feed intake and growth rate of Nile tilapia is still unclear and should be addressed in further studies.     

Effect of totally or partially replacing fish meal by alternative protein sources on growth of African catfish Clarias gariepinus (Burchell, 1822) reared in concrete tanks

A 12‐week feeding trial was carried out in concrete tanks to examine complete and partial replacement (75%) of fish meal (FM) with poultry by‐product meal (PBM), meat and bone meal (MBM) and soybean meal (SBM) in practical feeds for African catfish Clarias gariepinus. Triplicate groups of fish (initial body weight ranged from 90.33 to 93.93 g fish⁻¹) were fed seven isonitrogenous and isocaloric diets of 20% digestible protein and 300 kcal 100 g⁻¹ of digestible energy. The control contained 25% herring meal, whereas in the other six diets, PBM, MBM and SBM replaced 75% or 100% of the FM. Final body weight (FBW) and specific growth rate (SGR) of the fish fed diets containing PBM (75% and 100%), SBM (75% and 100%) and MBM (75%) were all higher, but not significantly different than those for fish fed the control diet. Replacing 100% of the FM by MBM significantly lowered FBW and SGR. Concerning whole body composition, there were no significant differences in ash and gross energy content of whole‐body among fish; fish fed diets containing PBM‐100% recorded significantly lower protein content compared with the control diet, while fish fed diet SBM‐100% recorded significantly lower moisture content compared with the control diet. Also fish fed diets SBM‐100% and PBM‐75% recorded higher lipid and gross energy contents compared with the control diet. The study revealed that satisfactory growth and feed utilization responses could be achieved through the replacement of FM by PBM, SBM and MBM in the diet of African catfish.     

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.