Assessment of Compensatory Growth in Channel Catfish Ictalurus punctatus R. and Associated Changes in Body Condition indices

A feeding trial was undertaken to evaluate compensatory growth in channel catfish and to chronicle the changes in body condition associated with the imposed feeding strategy. Four 1200-L circular tanks were each stocked with approximately 600 fingerling channel catfish (mean initial weight 32 g). Two tanks represented control fish which were fed to apparent satiation once daily throughout the trial. The two remaining tanks of fish were unfed for 4 wk and subsequently refed daily to apparent satiation for the following 10 wk in order to elicit a compensatory growth response. Fish fed to apparent satiation during the first 4 wk of the trial had a 41% increase in body weight, while the fasted fish decreased in weight by 20%. During the subsequent refeeding period, previously unfed fish were not able to increase growth rates sufficiently to overcome weight loss imposed by the 4-wk feed restriction. However, after 8 wk of refeeding, total increase in body weight of the previously unfed fish was 179 % of initial weight and similar to that of control fish which gained 231 % of initial weight. Hepatosomatic index (HSI) and condition factor decreased rapidly during the fasting period and increased rapidly to control levels during subsequent refeeding. The intraperitoneal fat (1PF) ratio and muscle ratio responded more slowly to feed restriction with IPF ratio decreasing consistently after 2 wk feed restriction. Muscle ratio showed little effect from the 4-wk period of feed deprivation. It appears that not feeding channel catfish fingerlings for 4 wk is too long to induce a compensatory growth response that is optimal for aquaculture; however, HSI may be the index of choice for detecting when refeeding should begin to maximize compensatory growth.     

Effect of Restricted Feeding Regimes on Compensatory Growth and Body Composition of Red Sea Bream, Pagrus major

Compensatory growth of red sea bream, Pagrus major, during feed deprivation and after refeeding was investigated. Groups of three fish each were allocated into 28 cages. Fish were fed by a commercial feed to satiation twice a day. Four feeding groups of fish were prepared: one group with continuous feeding (C) for 9 wk and three other groups with feed deprivation for 1 wk (F1) in Week 3, 2 wk (F2) from Week 2 to Week 3, and 3 wk (F3) from Week 1 to Week 3, respectively. All fish in the feed deprivation treatments resumed feeding in Week 4. The full compensatory growth was achieved in F1 and F2 fish after refeeding for the first 3 wk but in F3 fish after refeeding for the second 3 wk. Specific growth rate and feed conversion efficiency in all fish experiencing fasting were higher than those of control fish after first 3 wk of refeeding. At the end of feed deprivation in Week 3, crude protein, crude lipid, and energy content of all fish experiencing fasting were lower than those of the control fish. These results indicated that red sea bream experienced 1‐, 2‐, and 3‐wk fasting could achieve full compensatory growth in the 9‐wk feeding trial.     

Compensatory growth response of Sparus aurata following different starvation and refeeding protocols

A feeding trial evaluated the influences of different cycles of starvation and refeeding protocols for 7 weeks on growth and feed intake in 14‐g gilthead sea bream, Sparus aurata. Following 7 weeks of alternated cycles, all the groups were fed to apparent satiation for a further 3 weeks. Three groups of fish were fasted for 2, 4 or 7 days (S2, S4 and S7, respectively) and then refed until their relative feed intake differed by less than 20% of fed controls until the end of the week 7, while a fourth group (S7/Rf14) experienced three cycles, each consisting of 1 week of food deprivation followed by 2 weeks of satiation feeding. Control (C) fish were fed to satiation throughout the trial. The fish were fed a sea bream diet (450 g kg^?1 crude protein) according to the protocols, twice a day for 7 weeks. Growth performance and feed intake in continuously fed control group were significantly higher than those of the deprived groups (S2, S4, S7 and S7/Rf14) (P < 0.05). Weight gain highly correlated with total feed intake (R² = 94), and feed efficiency was the highest in the control group than other deprived groups (P < 0.05). The juveniles of gilthead sea bream demonstrated only a partial compensation during the cycling period and even after being fed to satiation for another 3 weeks. The convergence of growth trajectories and subsequent hyperphagic responses of the groups fed according to protocols are discussed in terms of possible costs of compensatory growth.     

Effects of feeding frequency and feed type on the growth,feed utilization and body composition of juvenile olive flounder,Paralichthys olivaceus

A factorial (3 × 4) feeding trial was conducted to investigate the effects of feeding frequency and feed type on the growth performance, feed utilization and body proximate composition of juvenile olive flounder. Three feed types including a sinking moist pellet (MP), a sinking dry pellet (DP) and a floating extruded pellet (EP) were used. Fish (average weight, 11.1 ± 0.4 g) were randomly distributed in thirty‐six 300 L tanks in a flowthrough system. Triplicate groups (30 fish per tank) of fish were fed each feed type to visual satiation at three meals per day, two meals per day, one meal per day and one meal every 2 days for 7 weeks. At the end of the feeding trial, the survival of fish was not significantly different among the treatments. Weight gain was affected by the feeding frequency. The highest weight gain was observed in fish fed the EP at three meals per day. The daily feed intake of fish fed the MP and DP tended to be higher than that of fish fed the EP at each feeding frequency. The feed efficiency and the protein efficiency ratio of fish fed the EP were higher than those of fish fed the MP and DP. The body proximate composition of fish was altered by the feeding frequency. The crude lipid content increased with the increase in the feeding frequency. The present findings suggest that three feedings per day at visual satiation of the floating EP may be sufficient for the maximal growth performance of olive flounder grown from 11 to 60 g.     

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.     

The effects of ration level on feed intake and growth, and compensatory growth after restricted feeding, in turbot Scophthalmus maximus L.

Feed intake and growth were studied in groups of turbot fed daily rations of 0.25%, 0.38% and 1% of body weight day^–1 for 41 days. Then, all groups were fed 1% of body weight day^–1 for the next 34 days. The two restricted rations resulted in reduced growth rates (30% and 60% of fully fed controls), and there was a tendency for increased growth heterogeneity (coefficient of variation increased from about 100% to about 150%) compared with controls on full rations. Nevertheless, restricted rations did not result in any increase in size heterogeneity with the passage of time: the coefficient of variation for weight changed little irrespective of feeding treatment. The turbot became hyperphagic and displayed compensatory growth after the change from restricted to excess feeding, with compensatory growth being most marked among the fish that had been subject to the most severe feed restriction. The results provided some evidence of increased variability in feeding and growth within groups of turbot fed restricted rations, possibly as a result of the establishment of weak feeding hierarchies. When feeding restrictions were lifted, the turbot that had reduced growth under feed restriction were able to completely compensate for lost growth.     

Growth performance, body composition and plasma thyroid hormone status of channel catfish (Ictalurus punctatus) in response to short-term feed deprivation and refeeding

A 6-week feeding trial was conducted to investigate the effects of short-term feed deprivation on inducing compensatory growth and changes in thyroid hormone levels of channel catfish. Feeding treatments consisted of the following four regimes of 2-week duration: satiate feeding (control), no feed for 3 days then feeding to apparent satiation for the next 11 days, no feed for 5 days then feeding to apparent satiation for 9 days, and no feed for 7 days then feeding to apparent satiation for 7 days. These regimes were repeated three times over the 6-week trial in which 25 channel catfish fingerlings, initially averaging 15 g each, were stocked into each of 12, 38-l glass aquaria supplied with supplemental aeration and flow-through water. Depriving fish of feed had a pronounced effect in that fish lost weight in as little as 3 days. Returning the fish to a satiate feeding regime caused a resumption of growth, equal to control growth only in the case of the 3-day deprived treatment, but all periods of feed deprivation failed to induce a period of catch-up growth adequate to compensate for previously lost weight. Feed efficiency also was not improved by the periods of feed deprivation, and restricting feed in excess of 3 days lowered feed efficiency. Fish condition indices were not altered at the termination of the trial. Muscle lipid, muscle protein and liver protein also were not different among feeding regimes. Liver lipid was elevated in fish deprived of feed for more than 3 days every 2 weeks. Plasma thyroxine (T₄) and triiodothyronine (T₃) were equally depressed by 3 days from the onset of feed deprivation. Both hormones rose significantly within 24 h of realimentation, with the greatest increase observed in animals subjected to the briefest feed deprivation. These results support a role for thyroid hormones in the promotion of growth in channel catfish. Whereas feed deprivation appears to rapidly reduce activity of the hypothalamo-pituitary-thyroid axis, the high correlation observed between T₄ and T₃ in all treatments suggests that peripheral deiodinating systems are capable of rapidly generating T₃ from T₄ upon realimentation. More rapid recovery of thyroid hormone production following realimentation may minimize the effects of feed deprivation on growth and feed efficiency of fish subjected to the 3-day deprivation treatment when compared to longer periods.     

Compensatory Growth of Juvenile Flounder Paralichthys olivaceus L. and Changes in Biochemical Composition and Body Condition Indices during Starvation and after Refeeding in Winter Season

Compensatory growth and changes in biochemical composition, hematocrit and body condition indices of juvenile flounder Paralichthys olivaceus were assessed during starvation and after refeeding. Twenty juvenile fish were stocked into each 200‐L flow‐through tank to give five treatments with three replicates per treatment: control group fish (C) were hand fed to apparent satiation twice daily for 8 wk, whereas the Sl, S2, S3, and S4 fish were hand fed to apparent satiation twice daily for 7, 6, 5, and 4 wk after 1, 2, 3, and 4 wk of starvation, respectively. During starvation, weight decreased linearly with periods of feed deprivation up to 3 wk. Survival was not significantly different among treatments. At the end of the feeding trial, weight gain (g/fish) and specific growth rate (SGR) of flounder in S2 was significantly (P < 0.05) higher than those of fish in S3 or S4, but not significantly different from those of fish in C or Sl. Feed consumption of flounder (g/fish) was proportional to duration of feeding except for that of fish in S2. Feed efficiency ratio (FER) and protein efficiency ratio (PER) values for flounder in S2 were significantly (P < 0.05) higher than those for fish in C, but not significantly different from those for fish in Sl, S3, or S4. During starvation, hepatosomatic index (HSI) and lipid content of flounder without liver decreased with periods of feed deprivation. However, HSI and condition factor (CF) for flounder in S2 were significantly (P < 0.05) higher than those for fish in Sl, S3, S4 and C except for CF in Sl at the end of the feeding trial. Proximate composition of flounder without the liver was not significantly different among treatments at the end of the feeding trial. In considering above results, juvenile flounder achieved compensatory growth with up to 2‐wk feed deprivation. Compensatory growth of flounder fed for 6 wk after 2‐wk feed deprivation was well supported by improvement in SGR, FER, and PER. HSI could be a good index to monitor changes in body condition during starvation and after refeeding.     

Phosphorus requirement of European sea bass (Dicentrarchus labrax L.) juveniles

A growth trial was conducted to estimate the phosphorus requirement of European sea bass juveniles. Six experimental isonitrogenous and isoenergetic semi‐purified diets (casein based) were formulated to contain 0.48%, 0.65%, 0.77%, 0.86%, 1.05% and 1.25% phosphorus (diets D1, D2, D3, D4, D5 and D6 respectively). Dicalcium phosphate was used as dietary phosphorus source. Twelve groups of 25 fish of 10 g initial body weight were allocated to 55‐L tanks in a thermoregulated water recirculating system. Each experimental diet was assigned to duplicate groups of these fish. The trial lasted for 10 weeks and fish were fed two times a day, 6 days a week, to apparent visual satiation. At the end of the trial, final weight of fish fed diet D1 was significantly lower than that of the other groups, except of fish fed diet D4. Mortality of fish fed diet D1 was significantly higher than that of fish fed the other diets, except for diet D6. Feed efficiency and protein efficiency ratios were significantly lower with diet D1 than with the other diets. Nitrogen retention (% nitrogen intake) of fish fed diet D1 was significantly lower than in the other groups, except that of fish fed diet D4. Energy retention (% energy intake) was not significantly different among groups. At the end of the trial there were no differences in whole body composition among groups. Whole body phosphorus content averaged 0.72% (on a fresh weight basis) and was not significantly affected by dietary phosphorus content. Phosphorus retention averaged 6.1 g kg^?1 weight gain and was not significantly different among groups. Phosphorus retention (% phosphorus intake) was significantly higher in fish fed diets D2 and D3 than in fish fed higher dietary phosphorus levels. Expressed per unit body weight per day, phosphorus retention was not significantly different among groups fed diets D2 to D6, while phosphorus losses linearly increased with dietary phosphorus intake. Results of this trial indicate that the phosphorus requirement of sea bass juveniles was satisfied with a diet containing 0.65% of phosphorus.     

Effects of Periodic Feed Deprivation on Growth, Feed Efficiency, Processing Yield, and Body Composition of Channel Catfish Ictalurus punctatus

Two studies were conducted in 110‐L flow‐through aquaria and 0.4‐ha ponds to evaluate effects of periodic feed deprivation on the growth performance of channel catfish Ictalurus punctatus. Fish were deprived of feed 0, 1, 2, or 3 consecutive d/wk, l d per 5‐d period, or 3 consecutive d per 10‐d period and fed to satiation on days fish were fed. In Experiment 1, fish fed less frequently than daily consumed significantly less feed (over the experimental period) and gained significantly less weight than fish fed daily, except that feed consumption of fish deprived of feed 1 d/wk was not significantly different from that of fish fed daily. Compared with fish fed daily, fish deprived of feed 2 d/wk had significantly lower feed conversion ratio (FCR). Visceral fat of fish deprived of feed 1 or 2 d/wk was similar to that of fish fed daily, but fish deprived of feed for longer periods had significantly lower visceral fat than fish fed daily. Regression analysis indicated that feed consumption, weight gain, and visceral fat increased linearly as the number of days that fish were fed increased. In Experiment 2, there were no significant differences in the amount of feed fed between fish deprived of feed 1 d/wk and those fed daily. Net production of fish deprived of feed 1 or 2 d/wk or 1 d per 5‐d period was not significantly different from that of fish fed daily, but fish deprived of feed for longer periods had significantly lower net production than fish fed daily. Visceral fat of fish deprived of feed 1 d/wk or 1 d per 5‐d period was similar to that of fish fed daily, but fish on other treatments had significantly lower visceral fat than fish fed daily. Regression analysis showed that as the number of days fed increased the amount of feed fed and net production increased quadratically. Feed conversion ratio, carcass yield, visceral fat, and fillet fat increased, while fillet moisture decreased linearly as the number of days fed increased. Although feeding less frequently than daily may improve feed efficiency, and fish deprived of feed may demonstrate compensatory growth when a full feeding regime is resumed, it may be difficult to provide enough feed to satiate all size‐classes of fish under a multiple‐batch cropping system without causing water quality problems. Under normal economic conditions, fish should be fed daily to apparent satiation without waste and without causing water quality problems. However, during periods of unfavorable economic conditions, channel catfish raised from advanced fingerlings to market size may be fed less frequently than daily to reduce production cost. Results from the present study indicated that feeding channel catfish to satiation 5 or 6 d/wk (not feeding on one or two weekend days) could provide some benefits in reducing production cost through reduced feed and labor costs for food‐sized channel catfish during periods of low fish prices and high feed prices.     

Ration restriction,compensatory growth and pituitary growth hormone gene expression in Labeo rohita

An experiment to investigate the compensatory growth (CG) response of Labeo rohita was conducted in two phases: a first phase (6 weeks) in which triplicate groups of fish were subjected to feed restriction (5, 25, 50 and 75 % of satiation) or satiation feeding (control) and a second phase (6 weeks) of satiation feeding for all treatment groups. CG in body weight occurred in groups which were under moderate feed restriction (50–75 % of satiation) under phase 1, but more severe feed restrictions resulted in lower weight gain. Improved feed conversion ratio (FCR) (1.6 ± 0.05 and 1.9 ± 0.03) relative to control (2.1 ± 0.06) was observed in the fish that displayed CG following moderate feed restriction (50–75 % of satiation). At the end of the experiment, body moisture, lipid and protein content were not significantly different between moderately restricted fish and the control. After the first phase, there was no significant difference in the expression of pituitary growth hormone (GH) gene between groups, but at the end of the experiment, significantly lower GH expression was observed in the fish subjected to a restriction of 25 and 50 % of satiation during phase 1. Exploiting the ability of fishes to undergo CG in terms of weight gain and improved FCR without major changes in body composition can be considered as an effective management practice.     

Studies on the Nutrition of Spotted Sand Bass Paralabrax maculatofasciatus: Effect of the Dietary Protein Level on Growth and Protein Utilization in Juveniles Fed Semipurified Diets

Two feeding trials were conducted to determine the digestibility of a casein-based semi-purified diet and the effects of different protein levels on growth and protein use of spotted sand bass Paralabrax maculatofasciatus juveniles. For trial I, a semipurified diet with vitamin-free casein as the sole source of protein was fed three times a day to apparent satiation, for a period of 20 d. Feces were collected by siphoning each tank. The digestibility of the experimental diet was high: 97% for protein, 89% for lipids, and 84% for gross energy, whereas that of organic matter was 78%. For trial II, seven diets were formulated using vitamin-free casein at graded levels (25, 30, 35, 40, 45, 50, and 55% protein). Triplicate tanks for each dietary treatment were stocked with fish and fed by hand three times a day to apparent satiation for 6 wk. Perfomance of fish fed the different diets was evaluated for survival, percent weight gain, specific growth rate, feed conversion ratio, and protein efficiency ratio. Survival was 100% for all treatments. Growth of spotted sand bass juveniles increased as the dietary protein increased, but no evidence of reaching a plateau was found. The daily feed intake values showed an inverse relation to the protein content of the diets. The feed conversion ratio did not differ among diets containing 40% protein or greater. The results indicate that spotted sand bass juveniles with 2.5-g mean weight need at least 55% dietary protein for best growth when casein is the sole protein source. However, in terms of feed conversion ratio, the requirement apparently could be lower.     

Compensatory Growth of Pond-reared Hybrid Striped Bass, Morone chrysops × Morone saxatilis, Fingerlings

Compensatory growth (CG) or “catch‐up growth” is a period of super‐accelerated growth following a period of suboptimal conditions (i.e., lack of prey availability or overwintering). Little is known about the CG response in pond‐raised fish and whether hybrid striped bass (HSB), Morone chrysops × Morone saxatilis, might exhibit the rapid growth states or improvements in other production characteristics that may accompany the response. To evaluate the potential for CG in HSB culture, a 16‐wk growth trial in twelve 0.1‐ha earthen ponds was conducted. Approximately 2850 fish (mean weight ± SD = 3.2 g ± 1.1) were stocked into ponds and subjected to one of four cyclic feeding regimens. Treatment regimens included a control (0 wk, fed twice daily to apparent satiation) and cycles of 1, 2, or 4 wk of feed deprivation, followed by 1, 2, or 4 wk of feeding to apparent satiation. Fish in the 4‐wk feeding regimen were offered feed twice during the feed‐deprivation period (once every other week). Growth, specific growth rate (SGR), hepatosomatic index (HSI), intraperitoneal fat ratio, and condition factor (CF) were measured every other week, while overall growth, feed efficiency (FE) (FE = [weight gain/feed fed] × 100), and survival were calculated at the trial termination. The effect of these feeding regimens on water quality was examined by monitoring pH, turbidity, total ammonia nitrogen, nitrite–nitrogen, nitrate–nitrogen, soluble reactive phosphorus, and chlorophyll a weekly; total nitrogen and phosphorous biweekly; and dissolved oxygen and temperature twice daily. Cyclic feeding elicited CG; fish subjected to the 2‐wk regimen had a significantly higher SGR than 0‐wk controls during all but the final refeeding period. FE was higher for all fish in the cyclic regimens, although only FE for fish in the 2‐wk regimen was statistically greater (40%) than the controls. HSI was the most responsive measure and significantly decreased in the 2‐ and 4‐wk treatments during feed‐deprivation period and overcompensated during the refeeding period. CF also varied with feeding cycle and proved to be an effective nonlethal measure of predicting a CG response. No statistical differences in water quality parameters were observed. These data suggest that CG can be effectively induced in pond‐raised HSB and that the increase in FE warrants further research for practical application. Future pond studies with fingerling HSB fish should be conducted with emphasis on feed‐deprivation periods of 2 wk and refeeding periods of at least twice that of the feed‐deprivation period.     

Effect of feeding frequency on growth,feed efficiency and nutrient utilization of juvenile flounder (Platichthys flesus luscus)

An experiment was conducted to determine the effects of optimal feeding frequency on growth performance, feed efficiency, nutrient utilization and body composition in juvenile flounder. Four feeding frequencies of one (F1), two (F2), three (F3) and four (F4) times a day were evaluated as treatments in triplicate for a period of 60 days. Forty-seven hatchery produced juveniles (2.5 ± 0.7 g) were stocked into 160-L rectangular fiberglass tanks and fed with a commercial diet containing 54 % protein to satiation. At the end of the experiment, the final weight of F1, F2, F3 and F4 were 5.06 ± 0.29, 5.91 ± 0.42, 6.24 ± 0.42 and 6.16 ± 0.46 g, respectively. Growth rates and feed consumption were highest in F3 and lowest in F1. Feed conversion ratios ranged between 0.83 ± 0.04 and 0.90 ± 0.03. There were no significant differences in either moisture or ash content of the fish groups. Protein content decreased with increasing feeding frequency, while lipid content partly increased with increasing feeding frequency. Nitrogen intake and lipid intake were significantly higher in fish fed under F3 and F4 treatment, whereas the nitrogen gain decreased and lipid gain increased with increasing feeding frequency. It is concluded that the flounder juveniles can achieve maximum growth performance and better nutrient utilization when they are fed a given ration two times a day. The findings have practical significance toward establishing an appropriate flounder nursery rearing and will directly benefit the nursery operations.     

Voluntary feed intake,feed and nutrient utilisation in slow and fast growing rainbow trout strains

Two rainbow trout strains differing in their growth performance were used to study possible interactions between genotype, dietary composition and feed level on their feed utilisation efficiency and voluntary feed intake. Two diets (35 and 45 % of crude protein) and two feeding levels (to satiation or at a restricted level of 2 % of body weight), were used. The two diets were distributed, in duplicate, for each strain, during a four month growth trial. At the end of the experiment the digestibility of the two diets was determined in each strain, using chromic oxide, as a marker, and an automatic system for the faecal collection. The body composition of both strains was also analysed. The final weight of fish of the fast growing strain, fed to satiation, was significantly higher than that observed for fish of the slow growing strain. No significant differences were found between the strains's body weights, when a dietary restriction was made. Results observed for the feed-gain ratio were also similar between the two strains. The apparent digestibility coefficient (ADC) of dry matter and energy were significantly different between the two diets but similar for both strains. Concerning protein digestibility no significant differences were observed for diets, although one of the strains appeared to show a higher ADC for protein. Body composition as well as nitrogen and energy retention were similar for both diets and strains.     

The effect of dietary protein replacement by crystalline amino acid on growth and nitrogen utilization of turbot Scophthalmus maximus juveniles

A study was conducted to evaluate the effect of partial replacement of dietary fish meal by crystalline amino acids on growth performance, feed utilization, body composition and nitrogen utilization of turbot juveniles.

Four diets were formulated to be isolipidic (12% DM) and isonitrogenous (8% DM). A fish meal based diet was used as control. In the experimental diets, a crystalline amino acid (AA) mixture was used to partially replace fish meal, corresponding to a non-protein nitrogen content of 19, 37 and 56%, respectively (diets 19AA, 37AA and 56AA, respectively). The overall amino acid profile of the experimental diets resembled that of the whole-body protein of turbot. Each experimental diet was fed to triplicate groups of 20 fish (initial body weight of 31.8 g) twice daily to apparent satiation for 42 days. During the trial water temperature averaged 18 °C.

Final body weight, weight gain (g kg ABW^− 1 day^− 1) and specific growth rate were not different between the control and 19AA diet but significantly decreased with the increase of crystalline-AA inclusion from 19 to 56%. Feed intake and feed efficiency of fish fed the control and diet 19AA were similar and significantly higher than those of fish fed the 56AA diet. At the end of the growth trial, there were no significant differences in whole-body composition among groups. Hepatosomatic index was also unaffected by dietary treatments.

Nitrogen retention (g kg ABW^− 1 day^− 1) of fish fed the control and the 19AA diets were similar and significantly higher than that of fish fed the other diets. Expressed as a percentage of the nitrogen intake, N retention was significantly higher with the control than with the 37AA and 56AA diets.

Daily ammonia excretion (mg kg ABW^− 1 day^− 1) of fish fed the control diet was significantly higher than that of fish fed the 37AA and 56AA diets, while daily urea excretion (mg kg ABW^− 1 day^− 1) did not significantly differ among treatments. Non-fecal nitrogen (ammonia + urea) excretion (mg kg ABW^− 1 day^− 1) was significantly higher for fish fed the control diet than in those fed the 37AA and 56AA diets. However, as percent of N intake, ammonia excretion and non-fecal N excretion were significantly higher in fish fed the 56AA diet than in those fed the control and 19AA diets.

Specific activity of glutamate dehydrogenase, alanine and aspartate aminotransferases did not significantly differ among experimental groups.

In conclusion, in diets with an overall amino acid profile resembling that of the whole-body protein of turbot, crystalline-AA may replace 19% of dietary protein without negatively affecting growth performances or feed utilization efficiency. However, higher protein replacement levels of protein-bound-AA by crystalline-AA severely depressed growth performance.     

Effects of short-term feed restriction on production, processing and body shape traits in market-weight channel catfish, Ictalurus punctatus (Rafinesque)

The effects of feed restriction on channel catfish production, processing yield (carcass and fillet), visceral composition and body shape traits were determined. Channel catfish (initial mean weight =0.77 kg) were stocked into six 0.04‐ha ponds at ～5775 kg ha^?1. Two ponds were assigned to each of three feeding regimes for a 4‐week trial: fed daily to satiation, fed once weekly to satiation and not fed. Fish were measured for weight, processing yield and visceral components after 2 and 4 weeks, and for body shape after 4 weeks. Growth was fastest in fish fed daily, intermediate in fish fed weekly and slowest in unfed fish. There were no differences in survival among feeding regimes. After covariate adjustment for weight differences, fish fed daily had shorter, thicker bodies, and smaller heads than fish from feed‐restricted treatments. Carcass yield was higher for females than males and higher at week 2 than at week 4, but was not affected by feeding regime. Fillet yield was higher for females than males, higher at week 2 than at week 4, and higher for fish fed daily than for feed‐restricted fish (fed once weekly and not fed). Viscerosomatic index (VSI), visceral fat‐somatic index (VFI) and hepatosomatic index were higher at week 2 than at week 4, and highest for fish fed daily, intermediate for fish fed weekly and lowest for unfed fish. Hepatosomatic index and VSI were higher for females than males, but VFI was not different between genders. The female gonadosomatic index increased over time but was not affected by feeding regime. Short‐term feed restriction had negative impacts on growth and fillet yield. Processors could benefit by marketing severely feed‐restricted channel catfish as carcasses rather than fillets since fillet yield declined but carcass yield was unchanged by feed restriction.     

Draining system and feeding rate during the initial development of Lophiosilurus alexandri (Steindachner, 1877), a carnivorous freshwater fish

This study evaluated the efficiency of the drainage system during the larviculture of Lophiosilurus alexandri. Moreover, we assessed the best feeding rate after feed training for juvenile production. The study was performed in three phases over 87 days. In phase 1 (40 days), larvae were fed live food and posteriorly submitted to feed training in two drainage systems: water drained on the surface (DS), and water drained into a tank column (DI). In the second phase (30 days), using only the DS system juveniles were fed a formulated diet at feeding rates, 2, 4, 6 and 8% of body wet weight. In the third phase (17 days), the fish from the second phase were fed until apparent satiation. At the first phase, the animals in the DS system exhibited greater survival rates and growth. The best feeding rate for daily weight gain, specific growth rate (SGR) and mean body weights were similar: 5.57, 5.13 and 5.68% respectively. In the third phase, an increased SGR was observed in the treatment groups that received lower feeding rates in the second phase (2 and 4%), which could indicate a possible compensatory growth rate.     

投喂不同饵料对长薄鳅生长的影响

在水温18.6～21.6℃条件下,将初始体质量为(3.91±0.22) g的长薄鳅幼鱼随机分为5组,每组3个重复,每个重复10尾鱼,饲养在圆形玻纤缸(直径1 m、高0.8 m)中,分别投喂刀额新对虾、鳙鱼、配合饲料(粗蛋白≥46.0%)、虾+饲料、鱼+饲料5种饵料,以筛选适宜于长薄鳅幼鱼的适宜饵料投喂模式。75 d的饲养结果表明,不同投喂模式对长薄鳅的存活率无显著性影响(P>0.05),而对长薄鳅的生长影响显著(P<0.05)。试验结果表明,虾组、鱼组、饲料组、鱼+饲料组的长薄鳅最终体质量无显著性差异(P>0.05),但虾+饲料组最终体质量和体质量特定生长率显著高于其他4组(P<0.05),依次为虾+饲料组>饲料组>虾组>鱼组、鱼+饲料组。5个试验组鱼的体长特定生长率无显著性差异(P>0.05),依次为虾+饲料组>虾组>饲料组、鱼+饲料组>鱼组。试验结束时,各试验组鱼的生长离散均有所升高,生长离散变化依次为鱼组>鱼+饲料组>饲料组>虾组>虾+饲料组。各试验组长薄鳅的的摄食率差异显著(P<0.05),摄食率依次为鱼组>虾组>鱼+饲料组>虾+饲料组>饲料组;虾组和鱼组的饵料系数无显著性差异(P>0.05),但显著高于其他3组(P<0.05),其他3组间无显著性差异(P>0.05)。不同投喂模式下长薄鳅幼鱼的生长系数b值均小于3,呈负异速生长,但虾+饲料组的长薄鳅幼鱼生长系数b值最大。试验过程中各组鱼的肥满度均下降。研究结果显示,在本试验的不同饵料投喂模式中,投喂虾+饲料更利于长薄鳅的摄食和生长。     

中华鳖稚鳖继饥饿后的补偿生长研究

对中华鳖(Pelodiscus sinesis)稚鳖(平均体重4.47g)进行了6种饥饿处理:饥饿0(C)、3(T1)、6(T2)、9(T3)、12(T4)和15d(T5),然后饱食处理,实验持续28d。结果显示T1组与C组试验末体质量差异不显著,而显著高于其它饥饿处理组;摄食期的摄食率随饥饿处理时间延长而显著增加;T1组饵料系数与C组相近;T1组特定生长率最高,各组特定生长率差异不显著。表明:经过饥饿3d后恢复摄食的稚鳖可达到完全补偿,且补偿生长效应主要通过提高摄食率实现的。