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.     

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.     

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.     

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.     

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.     

Optimum histidine requirement of fry African catfish, Clarias gariepinus (Burchell)

Dietary histidine requirement of fry African catfish, Clarias gariepinus (2.57 ± 0.02 cm; 0.22 ± 0.03 g) was quantified by feeding casein–gelatin-based isonitrogenous (40% crude protein) and isocaloric (17.90 kJ g⁻¹ gross energy) amino acid test diets with graded levels of histidine (0.25%, 0.30%, 0.35%, 0.40%, 0.45% and 0.50% dry diet) in eighteen 80 L indoor circular aqua-coloured troughs provided with the flow-through system for 12 weeks. Maximum absolute weight gain (2.66), best feed conversion ratio (1.29), highest protein efficiency ratio (1.94), protein retention efficiency (34%) and energy retention efficiency (70.4%) were achieved at 0.40% dietary histidine. Broken-line and non-linear regression models were adopted to assess dietary histidine requirement for C. gariepinus . When analysed using broken-line regression model these parameters were also best at 0.40% dietary histidine corresponding to 1.0% protein, respectively, whereas using second-degree polynomial regression analysis, histidine requirement was obtained at 0.42%, 0.41%, 0.40%, 0.41% and 0.41% of dry diet, corresponding to 1.05%, 1.02%, 1.0%, 1.02% and 1.02% protein respectively. Based on the broken-line and second-degree polynomial regression analyses of the growth and nutrient retention data, optimum histidine requirement of fry C. gariepinus was found to be in the range of 0.40–0.42% dry diet, corresponding to 1.0–1.05% of dietary protein.     

Replacement of fish meal with poultry by-product meal in practical diets for redclaw crayfish (Cherax quadricarinatus)

Aquaculture of redclaw crayfish, Cherax quadricarinatus, is rapidly developing in tropical and sub‐tropical regions of the world. As the industry is still in its infancy, grow out diets are generally not formulated specifically for this species as there is limited data on nutrient requirements and the acceptability of various ingredients. Given the recent increases in the price of fish meal (FM), the use of alternative protein sources such as poultry by‐product meal (PBM) may be more cost effective. The present research evaluated the response of juvenile redclaw to practical diets utilizing PBM as a replacement for FM. Juvenile redclaw crayfish (0.45 g ± 0.01) were stocked into 24, 600‐L, outdoor round tanks at a density of 12.5 m^?2. Tanks were supplied water from a watershed reservoir and maintained on a flow through regime. Crayfish in four replicate tanks were maintained on one of the six diets formulated to contain 260 g kg^?1 crude protein and 70 g kg^?1 crude fat which had previously demonstrated good growth under similar conditions. FM in the basal diets was replaced with PBM at various levels, on an iso‐nitrogenous basis, so that the diets contained 150, 120, 90, 60, 30 and 0 g FM kg^?1 diet and 78, 105, 132, 158, 185 and 212 g PBM kg^?1 diet, respectively. At the conclusion of the 56‐day growth trial, survival (>83%) and growth (>11.3 g or 2400%) of the crayfish were not significantly different among treatments. Based on these results, PBM appears to be a viable candidate as a replacement for FM in redclaw crayfish diets.     

The effect of diet and photoperiod on ammonia efflux rates of the African catfish, Clarias gariepinus (Burchell, 1822)

Total ammonia efflux rates of the African catfish, Clarias gariepinus (Burchell), were measured under different combinations of photoperiod (LD 24:0. LD 0:24, LD 12:12) and feeding regime (50% protein diet, 41% protein diet and zero food). A time-dependent variation of ammonia efflux following feeding was observed, with postprandial excretion rates in the first 12 h being greater than those in the following 12 h. Ammonia efflux rates were directly related to the level of protein in the diet under all photoperiod conditions. Photoperiod had no effect on ammonia efflux rate, except in the LD 24:0-high protein diet group, which may indicate a stress response.     

Substituting fish meal with poultry by-product meal in diets for black Sea turbot Psetta maeotica

A 60 days feeding experiment was carried out with Black Sea turbot Psetta maeotica to determine the amount of poultry by‐product meal (PBM) that could replace fish meal (FM) in formulated diets without reducing growth performance. Juvenile Black Sea turbot (initial average weight, 30 g) were fed five isoenergetic (gross energy, 20.5 ± 0.21 kJ g^?1 diet) and isonitrogenous diets (protein content, 550 ± 0.35 g kg^?1). The control diet used white FM as the sole protein source, the other four diets were prepared to replace FM protein at levels of 25%, 50%, 75% and 100% with PBM. The fish readily accepted all experimental diets and no mortality were recorded during the trial. There were no significant differences in growth performance of turbot (P < 0.05) fed the diets with 25% and 50% replacement levels compared with fish offered the control diet (100% FM), however, final body weight and specific growth rate values in the 50% replacement diet were about 8% lower than those of the control. Total nitrogen excretion in fish fed 50% replacement diet were about 10% higher than the control group, even though these parameters were not found to be statistically different. At the levels of 750 and 1000 g kg^?1 of the protein, PBM inclusion caused a severe decrease in growth performance, feed utilization, protein efficiency ratio and per cent nitrogen retention. The results in the present study indicate that up to 25% of FM protein can be replaced by PBM protein without causing reduction in growth performance, nutrient utilization and nitrogen retention.     

The urogenital papillae as an indicator of sexual maturity in male African catfish,Clarias gariepinus, (Burchell, 1822)

The present study investigated a non‐invasive method based on macroscopic morphological features of male Clarias gariepinus for the assessment of sexual maturity stage. As African catfish cannot be stripped for semen as in most other fish species; they have to be killed to obtain semen from the testes. This method could be used to ensure that males used to obtain sperm are sexually mature to increase the concentration and quality of mature sperm for egg fertilization in the production of C. gariepinus. Morphological features including the length and width of the urogenital papillae (UGP), an external secondary sexual characteristic of C. gariepinus (n = 89) were measured and calculated as a percentage of total body length. The urogenital papillae length (L_UGP) and width (W_UGP) index of each fish were used and compared with the macroscopic and microscopic maturity stage of the testes. The results revealed that although positive, a significant correlation does not exist between the L_UGP or W_UGP and maturity stage of the testes. Therefore, although this procedure would be valuable as an initial non‐invasive assessment of maturity, it does not provide an accurate or reliable indication of the maturity stage of the fish.     

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 consistency of individual differences in growth, feed efficiency and feeding behaviour in African catfish Clarias gariepinus (Burchell 1822) housed individually

Individual variation in growth, feed intake and feeding behaviour has been previously recognized in several fish species. However, there is a lack of information regarding the consistency of such individual differences, which is important to understand the probability of a certain individual trait to be inherent, i.e. genetically linked. The goal of this study is to quantify the consistency of individual differences in growth, feed intake/efficiency and feeding behaviour in African catfish Clarias gariepinus (Burchell 1822). Forty‐eight juvenile fish (58.9±0.4 g) were housed individually for 47 days and weighed every second week. The consistency of growth, feed efficiency (residual feed intake (RFI)) and feeding behaviour (total feeding time (TFT)) was determined using repeatability estimates. Fish exhibited pronounced individual variation in growth (CV=52.8%), feed intake (34.3%) and in the TFT (>100%). The repeatability estimates were 0.55 for growth, 0.70 for feed intake, 0.49 for RFI and 0.81 for TFT. Individual differences in growth were mainly explained by individual differences in feed intake (～80%). Individual differences in feeding behaviour contributed to explain differences in feed intake by affecting the RFI. With increasing TFT, the maintenance levels also increased suggesting that slow eaters were less efficient in feed/energy utilization. The results of this study indicate that individual differences in growth, feed intake/efficiency and feeding behaviour are consistent over time and therefore probably inherent. Moreover, this study may have implications on the use of feeding behaviour as a predictor of feed efficiency in juveniles of African catfish.     

Urea and ammonia excretion by embryos and larvae of the African catfish Clarias gariepinus (Burchell 1822)

Yolk-sac larvae and starved larvae of Clarias gariepinus (Burchell 1822), reared at 28°C, were predominantly ammonotelic, but urea excretion contributed about 19±7% to the total nitrogen excretion. Exogenously feeding larvae of C. gariepinus were mainly ammonotelic until 180-205 h post fertilization, but from then on the relative urea excretion stabilized at 44±13%. The contents of total free amino acids (FAA) and ammonia in C. gariepinus peaked around complete yolk absorption. During the first period after hatching 64% of the FAA and 60% of the total ammonia were located in the yolk compartment. The body compartment contained the highest amount of FAA and total ammonia at the end of the yolk-sac period (65 and 77%, respectively). The amount of nitrogen originating from catabolism of amino acids was balanced within 6% by the excreted sum of ammonia and urea. The high degree of ureotelism in C. gariepinus larvae may constitute an adaptive mechanism to a habitat of temporal water shortage.     

Effect of replacement of dietary fish meal by meat and bone meal and poultry by-product meal on growth and feed utilization of gibel carp, Carassius auratus gibelio

Triplicate groups of gibel carp Carassius auratus gibelio (initial body weight: 5.25 ± 0.02 g) were fed for 8 weeks at 20–25 °C on five isonitrogenous (crude protein: 400 g kg^?1) and isoenergetic diets (gross energy: 17 kJ g^?1). Meat and bone meal (MBM) or poultry by‐product meal (PBM) were used to replace fish meal at different levels of protein. The control diet contained fish meal as the sole protein source. In the other four diets, 150 or 500 g kg^?1 of fish meal protein was substituted by MBM (MBM₁₅, MBM₅₀) or PBM (PBM₁₅, PBM₅₀). The results showed that feeding rate for the MBM₅₀ group was significantly higher than for other groups except the PBM₅₀ group (P < 0.05). Growth rate in the MBM₁₅ group was significantly higher than that in the control (P < 0.05), while there was no significant difference in growth between the control and other groups (P > 0.05). Feed efficiency and protein efficiency ratio in MBM₅₀ was significantly lower while that in MBM₁₅ was significantly higher (P < 0.05). Replacement of fish meal by MBM at 500 g kg^?1 protein significantly decreased apparent dry matter digestibility (ADC_D) and gross energy (ADC_E) while apparent protein digestibility (ADC_P) was significantly decreased by the replacement of MBM or PBM (P < 0.05). The results suggest that MBM and PBM could replace up to 500 g kg^?1 of fish meal protein in diets for gibel carp without negative effects on growth while 150 g kg^?1 replacement by MBM protein improved feed utilization.     

Effect of feeding time and frequency on the growth and feed utilization of African catfish Clarias gariepinus (Burchell 1822) fingerlings

The effects of feeding time and frequency on the growth, feed utilization and survival of Clarias gariepinus (Burchell 1822; family Clariidae) fingerlings were evaluated in a 25-day study. Groups of African catfish with an initial individual weight of 0.98 ± 0.02 g were offered feeds continuously for 24 h, or during the day or night at different time intervals, with varying meal size. The growth rate was significantly affected by meal times. Widely practised day time feeding with three equal size meals a day gave the lowest growth and highest food wastage. The growth rates of fish fed continuously or during night time following their feed demand were significantly higher with lowest food conversion ratios and food wastage.     

不同饲料蛋白水平下点带石斑鱼对鸡肉粉、羽毛粉和血粉混合物的利用能力

通过10周网箱养殖实验,评价了不同饲料蛋白水平下点带石斑鱼对1种鸡肉粉、羽毛粉和血粉混合物的利用能力。采用2×4实验设计,设2个饲料蛋白水平(490 g/kg和530 g/kg粗蛋白),每个饲料蛋白水平下设4个鱼粉水平,其中1组饲料中加入500 g/kg鱼粉(对照),另外3组饲料中分别加入139、278、416 g/kg的鸡肉粉、羽毛粉和血粉混合物(鸡肉粉∶羽毛粉∶血粉=65∶20∶15)替代对照饲料中30%、60%、90%的鱼粉。实验鱼初始体重为(33.4±0.1) g。实验期间,除恶劣天气外,每天分两次按饱食量投喂实验鱼。实验结果表明,饲料蛋白水平对摄食量、增重,饲料系数、氮储积效率、能量储积效率和鱼体组成无显著影响;饲料鱼粉含量显著影响增重,饲料系数、氮储积效率和能量储积效率,但对摄食量和鱼体组成无显著影响。在相同饲料蛋白水平下,特定生长率(SGR)随鱼粉含量降低而下降;当鱼粉含量相同时,摄食高蛋白饲料的鱼SGR略高于摄食低蛋白饲料的鱼。本实验结果显示,通过添加鸡肉粉、羽毛粉和血粉混合物可将点带石斑鱼饲料鱼粉含量降低到200 g/kg,在490~530 g/kg范围内提高饲料蛋白水平无助于降低点带石斑鱼饲料鱼粉含量。     

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.