Protein and energy nutrition of brook trout (Salvelinus fontinalis) at optimal and elevated temperatures

The digestible protein (DP) and digestible energy (DE) requirements for maintenance and growth of brook trout (Salvelinus fontinalis) were determined using a factorial model at either optimum (15 °C) or elevated temperature (19 °C). Several key parameters of the factorial model were measured using a series of inter‐related studies. The maintenance requirements for DP and DE were 0.10 gDP kg^?0.69 day^?1 (15 °C) and 0.31 gDP kg^?0.78 day^?1 (19 °C), and 34.86 kJDE kg^?0.84 day^?1 (15 °C) and 46.14 kJDE kg^?0.86 day^?1 (19 °C). The total requirements for DP were 0.10 gDP kg^?0.69 day^?1 + 2.14PG (protein gain) (15 °C) and 0.31 gDP kg^?0.78 day^?1 + 1.98PG (19 °C). The total requirements for DE were 36.86 kJDE kg^?0.84 day^?1 + 1.58EG (energy gain) (15 °C) and 46.14 kJDE kg^?0.86 day^?1 + 1.64EG (19 °C). The partial efficiencies for growth were 0.47 (15 °C) and 0.51 (19 °C) for protein, and 0.63 (15 °C) and 0.61 (19 °C) for energy. Nutrient gain was lower at the elevated temperature; however, feed formulation for brook trout should be adjusted to match changes in nutrient requirements at different culture temperatures. The protein and energy requirements model will be useful for developing commercial feeds and feeding charts for brook trout.     

Effect of feeding level on growth and nutrient deposition in rainbow trout (Oncorhynchus mykiss Walbaum) growing from 150 to 600 g

The effects of feeding level on growth and energy partitioning were studied in rainbow trout growing from 150 to 600 g. Triplicate groups of fish (initial weight 158 g fish^?1) were fed a practical diet at various feeding levels (25%, 50%, 75% and 100% of near satiation) for 24 weeks at 8.5°C. The final body weights of fish were 235, 381, 526 and 621 g. Restricted feeding levels significantly reduced live weight gain. Feeding levels had less pronounced effects on feed efficiency ratio, which were 0.98, 1.08, 1.02 and 0.83, respectively, for the 25%, 50%, 75% and 100% feeding levels. The growth of fish fed to near satiation was accurately described by the thermal‐unit growth coefficient. The growth data also showed that the widely used specific growth rate was not an appropriate model. Fish fed at the lowest feeding level (25%), which represented a maintenance ration (energy gain was less than 2 kJ fish^?1 day^?1), showed positive protein deposition but negative lipid deposition. This indicates that fish fed a maintenance ration mobilize body lipid reserve to support protein deposition. The efficiency of energy for growth (k_g) was estimated to be 0.63. The factorial multiple regression approach estimated that the partial efficiencies of metabolizable energy utilization for protein deposition (k_p) and lipid deposition (k_f) were 0.63 and 0.72, and that maintenance energy requirement was about 19 kJ (kg BW^0.824)^?1, for rainbow trout held at 8.5°C.     

The effect of food type (formulated diet vs. natural) and fish size on feed utilization in common sole,Solea solea (L.)

This study compares the effect of food type (formulated diet vs. natural food) and fish size on protein and energy utilization efficiencies for growth in common sole, Solea solea (L.). Replicate groups of common sole (mean initial body weight ± SD was 45.7 g ± 2.1 and 111.2 g ± 4.2) received the diets at five (natural feed) or four (formulated diet) feeding levels. The protein utilization efficiency for growth (k_gCP) was higher (P > 0.001) in common sole fed ragworms than in common sole fed the formulated diet (respectively, 0.40 and 0.31). Likewise, the energy utilization efficiency for growth (k_gGE) was higher (P = 0.001) in common sole fed ragworms than in common sole fed the formulated diet (respectively, 0.57 and 0.33). The protein maintenance requirement was not different between food types (P = 0.64) or fish size (P = 0.41) being on average 0.82 g kg^?0.8 day^?1. The energy maintenance requirement was not different between food type (P = 0.390) but differed between fish size (P = 0.036). The gross energy maintenance requirement of small common sole was 35 kJ g^?0.8 day^?1. The gross energy maintenance requirement of large common sole was 25 kJ g^?0.8 day^?1. In conclusion, the low growth of common sole fed formulated diets was related to reduced feed utilization.     

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.     

Comparison of starch utilization in fingerlings of two Asian catfishes from the Mekong River (Pangasius bocourti Sauvage, 1880, Pangasius hypophthalmus Sauvage, 1878)

Five diets were formulated to provide an isoproteic daily dietary intake of 15 g kg^?1 day^?1, while maintaining daily starch intake ranging from 0 to 40 g kg^?1 day^?1. The 4‐week experiments started with initial mean weights of 4.7 and 4.4 g for Pangasius bocourti and P. hypophthalmus, respectively. The results clearly show the protein sparing action of starch in both species. Best protein retention was obtained with starch intake of 20 and 10 g kg^?1 day^?1 for P. bocourti and P. hypophthalmus, respectively, which was equivalent to 40 and 20% starch in the feed. Pangasius bocourti and P. hypophthalmus fingerlings attained maximal growth with starch intake of 30 and 10 g kg^?1 day^?1, equivalent to 60 and 20% starch in the feed. It was noted that body lipid accumulation was much higher in P. bocourti than in P. hypophthalmus, and that excess dietary starch intake depressed diet digestibility and growth.     

Comparative study on the effect of dietary lipid level on growth and feed utilization for gibel carp (Carassius auratus gibelio) and Chinese longsnout catfish (Leiocassis longirostris Günther)

An 8‐week growth trial investigated the effect of dietary lipid level on growth performance of a carnivorous fish, Chinese longsnout catfish (Leiocassis longirostris Günther) and an omnivorous fish, gibel carp (Carassius auratus gibelio). For each species, seven isonitrogenous semi‐purified diets (455 g kg^?1 crude protein for Chinese longsnout catfish and 385 g kg^?1 crude protein for gibel carp) were formulated to contain 30, 60, 90, 120, 150, 180 or 210 g kg^?1 lipid. For Chinese longsnout catfish, feed intake (FI) decreased with increasing dietary lipid and there was no significant difference in feed intake from 90 to 210 g kg^?1 lipid. Specific growth rate (SGR) increased with dietary lipid level (P < 0.05) and the 150 and 180 g kg^?1 groups were the best. Feed conversion efficiency (FCE), protein retention efficiency (PRE) and energy retention efficiency (ERE) were higher at 180 g kg^?1 lipid. For gibel carp, FI decreased with increased dietary lipid and 180 and 210 g kg^?1 lipid groups showed lower values. SGR increased with dietary lipid level and the 150 and 180 g kg^?1 were the best. FCE was higher at 180 g kg^?1 lipid level. PRE increased with dietary lipid level and there was no significant difference in groups from 120 to 210 g kg^?1 dietary lipid. ERE increased with increasing dietary lipid level, and groups fed 120, 150 and 180 g kg^?1 lipid showed the highest values. In Chinese longsnout catfish, increase in dietary lipid level, resulted in increased carcass dry matter, crude protein, crude lipid and gross energy. In gibel carp, dry matter, crude protein, and crude lipid increased with dietary lipid level. Based on regression between SGR and dietary lipid, dietary lipid requirements for Chinese longsnout catfish and gibel carp were 142.6 and 140.5 g kg^?1, respectively.     

Effects of dietary carbohydrate on weight gain and gonad production in small sea urchins,Lytechinus variegatus

In experiment 1, juvenile sea urchins (n = 80, 0.088 ± 0.001 g wet weight and 5.72 ± 0.04 mm diameter) were held individually and fed ad libitum one of three semi‐purified formulated diets (n = 16 individuals treatment^?1). In the diets, protein was held constant (310 g kg^?1 dry, as fed) and carbohydrate level varied (190, 260, or 380 g kg^?1 dry, as fed). Wet weights were measured every 2 weeks. Total wet weight gain was inversely proportional to dietary carbohydrate level and energy content of the respective diet. In experiment 2, sea urchins (5.60 ± 0.48 g wet weight, n = 40) fed 190 g kg^?1 carbohydrate consumed significantly more dry feed than those fed 260 g kg^?1, but not more than those fed 380 g kg^?1 carbohydrate. Based on differential feed intake rates, sea urchins that consumed more feed also consumed higher levels of protein and had the highest weight gain. Consequently, protein content and/or protein: energy ratio may be important in determining feed utilization and growth among sea urchins in this study. The average digestible energy intake was approximately 70 kcal kg^?1 body weight day^?1, suggesting daily caloric intake of juvenile Lytechinus variegatus is lower than in shrimp and fish.     

Effects of dietary protein to energy ratios on growth and body composition of juvenile Chinese sucker,Myxocyprinus asiaticus

A growth experiment was conducted to investigate effect of dietary protein to energy ratios on growth and body composition of juvenile Myxocyprinus asiaticus (initial mean weight: 10.04 ± 0.53 g, mean ± SD). Nine practical diets were formulated to contain three protein levels (340, 390 and 440 g kg^?1), each with three lipid levels (60, 100 and 140 g kg^?1), in order to produce a range of P/E ratios (from 22.4 to 32.8 mg protein kJ^?1). Each diet was randomly assigned to triplicate groups of 20 fish in 400‐L indoors flow‐through circular fibre glass tanks provided with sand‐filtered aerated freshwater. The results showed that the growth was significantly affected by dietary P/E ratio (P < 0.05). Fish fed the diets with 440 g kg^?1 protein (100 and 140 g kg^?1 lipid, P/E ratio of 31.43 and 29.22 mg protein kJ^?1) had the highest specific growth rates (SGR) (2.16 and 2.27% day^?1, respectively). However, fish fed the diet with 390 g kg^?1 protein and 140 g kg^?1 lipid showed comparable growth (2.01% day^?1), and had higher protein efficiency ratio (PER), protein productive value (PPV) and energy retention (ER) than other groups (P < 0.05). No significant differences in survival were found among dietary treatments. Carcass lipid content was positively correlated with dietary lipid level, but irrespective of protein level and inversely correlated with carcass moisture content. Carcass protein contents increased with increasing dietary lipid at each protein level. The white muscle and liver composition showed that lipid increased with increasing dietary lipid level (P < 0.05). Dietary protein concentrations had significant effect on condition factor (CF), hepatosomatic index (HSI) and viscerosomatic index (VSI) (P < 0.05). However, dietary lipid concentrations had no significant effect on CF, HSI (P > 0.05). Based on these observations, 440 g kg^?1 protein with lipid from 100 to 140 g kg^?1 (P/E ratio of 29.22 to 31.43 mg protein kJ^?1) seemed to meet minimum requirement for optimal growth and feed utilization, and lipid could cause protein‐sparing effect in diets for juvenile Chinese sucker.     

Effects of dietary protein and lipid levels and DP DE−1 ratio on growth, feed utilization and hepatosomatic index of juvenile haddock, Melanogrammus aeglefinus L.

Juvenile haddock, Melanogrammus aeglefinus L. (initial weight, 13.5 ± 0.1 g) were fed practical diets containing digestible protein to digestible energy (DP DE^?1) ratios of 25–30 g DP MJ DE^?1as‐fed using three protein levels (450, 500 and 550 g kg^?1) each at two lipid levels (110 and 160 g kg^?1) for 63 days. The results showed mean weight gain and feed conversion ratio were highest for diets containing 28.5 and 30.2 g DP MJ DE^?1. DP DE^?1 ratio had no significant effect on protein efficiency ratio except at the lowest level (24.7 g DP MJ DE^?1) indicating a protein sparing effect of higher lipid when dietary protein is below the requirement. Haddock appears to preferentially use protein as the prime source of DE. DP DE^?1 ratio had little effect on apparent digestibility (AD) of protein while AD of lipid was significantly affected. Significant differences in AD of energy and organic matter were found to be inversely related to the carbohydrate level of the diet. DP DE^?1 ratios of 28.5 g DP MJ DE^?1 or lower resulted in significantly higher hepatosomatic indexes. The highest whole‐body nitrogen gains and energy retention efficiencies were achieved at 28.5 and 30.2 g DP MJ DE^?1, whereas only slight differences in nitrogen retention efficiencies were observed. The highest levels of energy retained in the form of protein were achieved at 28.5 and 30.2 g DP MJ DE^?1. The diet that provided the best growth, feed utilization and digestibility with minimal HSI contained 546 g kg^?1 protein (513 g kg^?1 DP), 114 g kg^?1 lipid, 164 g kg^?1 carbohydrate, 17.0 MJ kg DE^?1 and a DP DE^?1 ratio of 30.2 g DP MJ DE^?1.     

Protein and energy utilization and the requirements for maintenance in juvenile mulloway (<Emphasis Type="Italic">Argyrosomus japonicus</Emphasis>)

This study describes the digestible protein (DP) and digestible energy (DE) utilization in juvenile mulloway, and determined the requirements for maintenance. This was achieved by feeding triplicate groups of fish weighing 40 or 129 g held at two temperatures (20 or 26°C), on a commercial diet (21.4 g DP mJ DE⁻¹) at four different ration levels ranging from 0.25% of its initial body weight to apparent satiation over 8 weeks. Weight gain and protein and energy retention increased linearly with increasing feed intake. However, energy retention efficiency (ERE) and protein retention efficiency (PRE) responses were curvilinear with optimal values, depending on fish size, approaching or occurring at satiated feeding levels. Maximum predicted PRE was affected by body size, but not temperature; PRE values were 0.50 and 0.50 for small mulloway, and 0.41 and 0.43 for large mulloway, at 20 and 26°C respectively. ERE demonstrated a similar response, with values of 0.42 and 0.43 for small, and 0.32 and 0.34 for large mulloway at 20 and 26°C respectively. Utilization efficiencies for growth based on linear regression for DP (0.58) and DE (0.60) were independent of fish size and temperature. The partial utilization efficiencies of DE for protein (k _p) and lipid (k _l) deposition estimated using a factorial multiple regression approach were 0.49 and 0.75 respectively. Maintenance requirements estimated using linear regression were independent of temperature for DP (0.47 g DP kg^−0.7 day⁻¹) while maintenance requirements for DE increased with increasing temperature (44.2–49.6 kJ DE kg^−0.8 day⁻¹). Relative feed intake was greatest for small mulloway fed to satiation at 26°C and this corresponded to a greater increase in growth. Large mulloway fed to satiation ate significantly more at 26°C, but did not perform better than the corresponding satiated group held at 20°C. Mulloway should be fed to satiation to maximize growth potential if diets contain 21.4 g DP mJ DE⁻¹.     

Response of the tropical spiny lobster Panulirus ornatus to protein content of pelleted feed and to a diet of mussel flesh

In an 8‐week growth experiment, juvenile spiny lobsters (Panulirus ornatus) grew best on a feed containing at least 610 g kg^?1 crude protein on a dry matter basis (DM) and a digestible protein to digestible energy ratio of 29.8 mg kJ^?1. The study entailed a six treatment by four replicate randomized block experiment with 222 wild‐caught P. ornatus of mean initial weight (±SD) of 2.5 ± 0.19 g. The lobsters were fed one of five isolipidic feeds (approximately 130 g kg^?1 DM) in which the crude protein was serially incremented between 330 and 610 g kg^?1 DM, or a reference diet comprising the flesh of frozen green‐lip mussels. Lobsters fed the pelleted feeds had high survival (79 ± 4.5%) and responded to increasing dietary crude protein content with progressively higher growth rates, with the daily growth coefficient improving from 0.72% day^?1 with 330 g kg^?1 crude protein to 1.38% day^?1 with 610 g kg^?1 crude protein. Both growth rate and survival were low with the mussel diet (0.80% day^?1and 41 ± 4.5%, respectively). These results demonstrate that tropical spiny lobsters grow well when fed high‐protein, high lipid, pelleted feeds, but feeding on a sole diet of freshly thawed green‐lip mussels was unsatisfactory.     

Polka dot grouper Cromileptes altivelis fingerlings require high protein and moderate lipid diets for optimal growth and nutrient retention

An 8‐week comparative slaughter experiment was carried out to determine the effect of dietary protein and lipid on growth, apparent digestibility (AD) and nutrient retention of polka dot grouper Cromileptes altivelis. Fingerlings were fed diets that varied in crude protein (CP) at 55 g kg^?1 increments between 410 and 630 g kg^?1 dry matter (DM) and at either a moderate (150 g kg^?1 DM) or high (240 g kg^?1DM) lipid concentration. Each diet was fed to satiety twice daily to four replicate tanks (110 L) of fish. One replicate block of tanks comprised 150 fish of mean (±SD) initial weight of 9.6 ± 0.29 g, which were distributed equally to 10 tanks. The other three replicate blocks of tanks comprised 300 fish of 12.6 ± 0.45 g, which were distributed equally to 30 tanks. Tanks were provided with filtered and heated (29 ± 0.5 °C) seawater in a flow‐through system within a laboratory where photoperiod was maintained at 12 : 12 h light–dark cycle. Voluntary food intake was not significantly affected by either the CP or lipid concentration of the diet (mean ± SD of 1.93 ± 0.146 g week^?1) but there was a trend for intake to be higher on the moderate compared with the high lipid diets (mean ± SEM of 1.97 versus 1.89 ± 0.033 gweek^?1, respectively). Daily growth coefficient (DGC) and food conversion ratio (FCR) improved linearly (P < 0.01) with increasing dietary CP (from 0.94 to 1.35% day^?1 for DGC and 1.58 to 1.00 g DM g^?1 wet gain for FCR) and these responses were almost coincident for each of the lipid series. The AD of CP increased linearly with increasing dietary CP (from 46.8 to 74.1%) and was independent of dietary lipid. Apparent digestibility of energy increased curvilinearly with increasing dietary CP, with the quadratic component being more prominent for the high‐lipid series. Increasing the amount of lipid in the diet markedly increased the lipid content of the fish from an initial composition (mean ± SD) of 173 ± 7.3 g kg^?1 to a final composition (mean ± SEM) of either 217 or 250 ± 5.9 g kg^?1 for moderate and high‐lipid series, respectively. Total body lipid content tended to increase linearly with increasing dietary CP for the high‐lipid series but with an opposite effect for the moderate‐lipid series. The retention of digestible nitrogen decreased linearly with increasing dietary CP but at a steeper rate for the moderate, compared with the high, lipid series (from 62.7 to 35.7%, slope ?0.115 for moderate‐lipid and 54.6 to 41.9%, slope ?0.050 for high‐lipid). A quadratic function of dietary CP concentration best explained the retention of digestible energy with the curvilinearity being more marked for the high, compared with the moderate, lipid diet series. While there was some indication that ingested lipid spared dietary protein, the results showed a far greater propensity of polka dot grouper fingerlings to use protein as the prime dietary energy source. Diets for juvenile polka dot grouper should contain not less than 440 g digestible protein kg^?1 DM and at least 150 g lipid kg^?1 DM.     

Dietary protein requirement of zebra sea bream (Diplodus cervinus,Lowe 1838) juveniles

A 14 weeks growth trial was performed to estimate the protein requirement for growth and maintenance of zebra sea bream (Diplodus cervinus) juveniles. For that purpose, nine isolipidic diets were formulated to contain increasing protein levels (from 50 to 550 g kg^?1) at the expense of carbohydrate. Each diet was assigned to duplicate groups of 20 fish, with an average body weight of 7.7 g. Feed efficiency improved with dietary protein up to 400 g kg^?1, no further differences being noticed at higher protein levels. Fish fed the 50 g kg^?1 protein diet lost weight during the trial. In the other groups, weight gain improved as dietary protein increased up to 350–400 g kg^?1. Fish fed diets with 250 g kg^?1 protein or lower had lower whole‐body protein content than the other groups. A curvilinear‐plateau model was used to adjust weight gain and protein gain (g kg ABW^?1 day^?1) to dietary protein levels. Based on that model, the optimum dietary protein requirement for maximum weight gain was estimated to be 437.6 g kg^?1 and for maximum protein gain 461.9 g kg^?1, corresponding to a protein intake of 7.63 g kg ABW^?1 day^?1. Protein requirement for maintenance was estimated to be 1.01 g kg ABW^?1 day^?1.     

Effects of dietary protein and lipid levels on growth, feed conversion and body composition in rohu, Labeo rohita (Hamilton), fingerlings

Twelve experimental diets (D‐1 to D‐12) in a 4 × 3 factorial design (four protein levels: 250, 350, 400 and 450 g kg^?1 and three lipid levels: 50, 100 and 150 g kg^?1) were formulated. Carbohydrate level was constant at 250 g kg^?1. Rohu fingerlings (average wt. 4.3 ± 0.02 g) were fed the experimental diets for 60 days in three replicates at 2% BW  day^?1. Weight gain (%), specific growth rate (% day^?1) and feed gain ratio (FGR) indicated that diets containing 450 g kg^?1 protein and 100 or 150 g kg^?1 lipid (diets D‐11 and D‐12) resulted in best performance, although results were not significantly different from those of diet D‐9 (400 g kg^?1 protein and 150 g kg^?1 lipid). Protein efficiency ratio was highest with diets D‐6 (350 g kg^?1 protein and 150 g kg^?1 lipid) and D‐9 (400 g kg^?1 protein and 150 g kg^?1 lipid) (P > 0.05) and declined with higher and lower protein diets at all levels of lipid tested. Elevated lipid level (50, 100 or 150 g kg^?1) did not produce better FGR in diets containing 400 and 450 g kg^?1 dietary protein (P > 0.05). The combined effects of protein and lipid were evident up to 400 g kg^?1 protein. Growth and FGR showed consistent improvement with increased lipid levels from 50 to 150 g kg^?1 at each protein level tested except with diets containing 450 g kg^?1 protein. Apparent nutrient digestibility (for protein, lipid and energy) did not show significant variation among different dietary groups (P > 0.05). Whole body protein and lipid contents increased significantly (P > 0.05) with dietary protein level. The results of this study indicate that rohu fingerlings are adapted to utilize high protein in diets with varying efficiency. The fish could utilize lipid to spare protein but there is no significant advantage from this beyond the dietary protein level of 350–400 g kg^?1 in terms of growth and body composition.     

Influence of dietary fat level and whole-body adiposity on voluntary energy intake by juvenile rainbow trout Oncorhynchus mykiss (Walbaum) under self-feeding conditions

The influence of dietary fat level and whole‐body adiposity on voluntary energy intake of juvenile rainbow trout Oncorhynchus mykiss (Walbaum) was examined using self‐feeders. Groups of lean fish [crude fat (CF) = 7%] and fat fish (CF = 11%), pretreated with a commercial diet with or without supplemental pollock oil, were self‐fed one of three fat level diets (CF = 8%, 13.5% and 19%) for 48 days at 17 °C. Final body weight (BW) and total digestible energy (DE) intake (kJ per fish) were positively affected by the initial BW. Relative to the initial BW, however, fat fish consumed less DE than lean fish. Although the effect of dietary fat level was not significant, percentage weight gain and daily DE intake per BW (kJ kg^?1 BW day^?1) of fat fish were significantly lower than those of lean fish (ancova with initial BW as a covariate, P < 0.05). Energy digestibility, feed efficiency and protein retention were improved with the dietary fat level; however, there was no difference resulting from body fat level. The whole‐body fat levels at the end of the experiment increased with the dietary fat level. Between groups self‐fed the same diet, fat levels of the initially fat fish were still higher than those of the lean fish. The results of the present medium‐term study suggest that rainbow trout adjust DE intake from diets with fat levels ranging from 8% to 19%. Although body fat level affects neither energy digestibility nor protein utilization, a high body fat level may reduce DE intake and consequently depress growth.     

Effects of feeding levels on growth performance,feed utilization,body composition and apparent digestibility coefficients of nutrients for juvenile Chinese sucker,Myxocyprinus asiaticus

An experiment was conducted to determine effects of feeding levels on growth performance, feed utilization, nutrient deposition, body composition and apparent digestibility coefficients (ADCs) of nutrients for juvenile Chinese sucker (initial weight, 11.77±0.22 g). Chinese sucker were fed a practical diet from 0% (starvation) to 4.0% (at 0.5% increments) body weight (bw) day^?1 for 8 weeks. The results showed that growth performance, feed utilization, nutrient deposition, body composition and ADCs of dry matter, protein and energy were significantly (P<0.05) affected by feeding levels. Survival was the lowest for the starvation group. Final mean body weight, growth rate, thermal‐unit growth coefficient (TGC) increased with feeding rate from 0% to 3.0% bw day^?1 (P<0.05) and showed no significant differences above the level (P>0.05). Feed conversion rate was significantly lower at a feeding level of 2.5% bw day^?1 than above and below the level (P<0.05). Protein efficiency ratio was markedly highest at the 2.5% bw day^?1 ration level (P<0.05). Fish fed at the feeding level (1.0% bw day^?1), which represented a maintenance ration (energy gain was less than 2.27 kJ fish^?1 day^?1), showed positive protein deposition but negative lipid deposition. This indicates that fish fed a maintenance ration mobilize body lipid reserve to support protein deposition. Lipid contents of whole body, muscle and liver increased with increasing feeding rates from 0.5% to 3.0% bw day^?1 and showed no significant differences above the level (P>0.05). Protein contents of whole‐body composition increased with feeding rate from 0.5 to 3.0% bw day^?1 (P<0.05) and showed no significant differences above the level (P>0.05), whereas muscle and liver remained relatively stable with the different ration amount with the exception of fish fed a ration of 0.5% bw day^?1, at which Chinese sucker possessed significantly lower body protein concentration (P<0.05). The ADCs of dry matter, protein and energy decreased with increasing feeding levels from 0.5% to 3.0% bw day^?1 and then remained relatively constant over the level. Based on the broken‐line regression analysis using WG data, the optimum and maintenance feeding levels for Chinese sucker were 3.10% bw day^?1 and 0.45% bw day^?1 respectively.     

Evaluation of heat-processed cocoa pod husk meal as an energy feedstuff in production diets for the clariid catfish, Clarias isheriensis (Sydenham)

Isoproteic and isoenergetic diets containing 0%, 15%, 30% or 45% heat-processed cocoa pod husk meal (CPHM) were fed to Clarias isheriensis (16.8 ± 2.4 g) for 180 days. Growth rates of catfish fed varying levels of CPHM were similar (P > 0.05). Differences in feed-gain ratio (FGR) or protein efficiency ratio (PER) between treatments were not significant (P > 0.05). Histology of the liver showed no pathological effects of incorporation of CPHM. In a second experiment, C. isheriensis (19.1 ± 3.5 g) were fed isoenergetic diets containing 250, 300, 350 and 400 protein g kg^?1 (protein: energy ratios of 21, 25, 29 and 33 mg protein.kJ^?1 DE, respectively). Growth rate and FGR improved (P < 0.05) in proportion to the dietary protein level. PER decreased with increase in dietary protein. Carcass protein was lowest (P < 0.05) in catfish fed 250 g protein kg^?1, but did not differ among the other diets (P > 0.05). Body fat was highest in catfish fed 250 g protein kg^?1 and lowest in fish fed 350 g protein kg^?1. These results indicate that CPHM may be a suitable carbohydrate energy source for clariids at a P:E ratio of approximately 29 mg protein.kJ^?1 DE.     

Effects of ration level on growth,nitrogenous excretion and energy budget of juvenile yellow catfish,Pelteobagrus fulvidraco (Richardson)

Growth, nitrogenous excretion and energy budget of juvenile yellow catfish, Pelteobagrus fulvidraco (initial body weight 1.17 ± 0.28 g) at various levels (50%, 60%, 70%, 80%, 90% and 100% satiation per day) were investigated with feeding diet containing 40% protein. Specific growth rate of yellow catfish increased (2.79–3.34% day) significantly (P<0.05) with ration level (RL) increasing. Feed conversion efficiency, feed protein retention efficiency and feed energy retention efficiency increased with the increase in RL, peaked at 70% of satiation, and then decreased at higher ration, with the ranges of 78.97–97.28%, 31.31–37.93% and 26.55–31.88% respectively. Both nitrogenous excretion (u, mg g^?1 day^?1) and faecal production (f, mg g^?1 day^?1) increased significantly with the increased RL, and ranged between 0.94–1.38 and 0.69–1.24 mg g^?1 day^?1 respectively. Apparent digestibility coefficients in dry matter, protein, energy decreased significantly as ration increased, with ranges of 54.42–69.64%, 78.24–89.90% and 69.66–82.07% respectively. Energy budgets of juvenile yellow catfish at satiation RL was: 100C=30F+8U+33R+29G or 100A=54R+46G.     

The growth performance of southern catfish fed diets with raw, precooked cornstarch and glucose at two levels

The ability of juvenile carnivorous southern catfish (Silurus meridionalis Chen) to use different levels, kinds and physic state (glucose, raw cornstarch and precooked cornstarch) of dietary carbohydrate was evaluated in term of growth performance. All diets contained 100 g kg^?1 lipid and 16 kJ metabolizable energy. Three isonitrogeneus (400 g kg^?1) diets were formulated to contain 150 g kg^?1 raw cornstarch, precooked cornstarch and glucose. Another three isonitrogeneus (300 g kg^?1) diets were formulated to contain 300 g kg^?1 raw cornstarch, precooked cornstarch and glucose. A control diet was formulated with no carbohydrate containing 500 g kg^?1 protein. Each experimental diet was fed to four tanks of 10 fish (28.3 ± 0.5 g) for 8 weeks at 27.5 °C. Specific growth rate (SGR) of 300 g kg^?1 glucose diet was significantly lower than those of other diets (P < 0.05). Feeding rates (FR) of 300 g kg^?1 glucose and control diets were significantly lower than those of the other diets (P < 0.05). Feed efficiency (FE) was significantly decreased with increased dietary carbohydrate level (P < 0.05). Feed efficiency of the 300 g kg^?1 glucose diet was significantly lower than those of the 300 g kg^?1 raw and precooked cornstarch diets (P < 0.05). The protein efficiency ratio (PER) was significantly increased with dietary carbohydrate level except that of the 300 g kg^?1 glucose diet, which was lowest among all diets (P < 0.05). The results suggested that both dietary starch and glucose were utilized for energy in southern catfish and had a protein‐sparing effect. At 150 g kg^?1 inclusion level, the utilization of raw and precooked cornstarch and glucose did not vary significantly, but a higher dietary glucose level (300 g kg^?1) had a markedly detrimental effect on growth in southern catfish.     

Evaluation of mixed feeding schedules with respect to compensatory growth and body composition in African catfish Clarias gariepinus

An 8‐week feeding trial was conducted in a recycling water system at 28 ± 1 °C to investigate compensatory growth and body composition in African catfish Clarias gariepinus (13.05 ± 0.05 g). A fishmeal‐based diet containing 350 g kg^?1 protein and 17.5 kJ g^?1 gross energy was fed to triplicate groups of 20 fish (per 30‐L tank). Fish were fed the diet either to satiation or feed restricted in six feeding schedules as satiation 56 days; restricted 28 days + satiation 28 days; restricted 14 days + satiation 14 days; restricted 7 days +satiation 7 days; restricted 3 days + satiation 4 days; and restricted 2 days + satiation 2 days. The restricted regime was achieved by offering fish 1% (maintenance ration) of their body weight per day adjusted after fortnightly weighing. African catfish showed partial compensatory growth under alternating periods of feed restriction and satiation feeding with significantly different values (P < 0.05) from fish fed in satiation throughout. However, significantly indifferent (P > 0.05) values of feed, protein, lipid and energy utilization were found under alternating periods of feed restriction and satiation feeding. Significantly higher (P < 0.05) feed intake was observed in treatment with satiation throughout than those in other treatments. All the feeding schedules showed no significant differences (P > 0.05) on body composition, organ indices, eviscerated carcass composition, viscera lipid and liver lipid. These studies reveals that C. gariepinus showed partial compensatory growth responses at alternating periods of restricted and satiation feeding.