In an attempt to identify appropriate feeding rates for multispecies of fish raised in fertilized earthen ponds, the present work was conducted over a 19week experimental period to establish the growth performance, production and body composition of Nile tilapia, common carp and silver carp fed 0.0%, 0.5%, 1.0%, 3.0%, 5.0% biomass and to apparent satiation (treatments). Twelve ponds were stocked with a similar number and weight of each fish species. Two ponds were assigned to each of the treatments, and a 25% protein pelleted fish feed was used to feed fish at the specified rate of feeding. At the end of the experiment, growth, weight gain, survival, yield and body composition of fish groups were affected by the treatments. The economic effectiveness also varied among treatments. The most conspicuous attribute of the feeding rates was its lack of influence on growth (g day À1 ), weight gain (g per fish), yield (kg ha À1 ) or body composition of silver carp. The results of whole-body proximate analysis indicated that various feeding rates had either an irregular pattern or no effects on the protein and ash gain per 100 g of fish body weight (bw) gain. The most notable exceptions were significant (P , 0.05) increases in body fat and gross energy gains in Nile tilapia, common carp and silver carp accompanied by decreases in percentages of moisture (but not in silver carp) as feeding rate increased. Among the six different feeding levels, feeding to apparent satiation (feed amount was equivalent to 2.67% of fish bw day À1 ) appeared to be optimal, as it significantly (P , 0.05) supported the highest fish production, income and net profit compared with all other treatments except for the 3% feeding level, for which the differences in those measurements were comparable.

A 12-week experiment was conducted to evaluate the suitability of gambusia (Gambusia affinis) fish meal (GFM) as a partial and complete substitute for the protein supplied by herring fish meal (HFM) in diets for red tilapia fingerlings (mean weight 0.42 g). Seven isonitrogenous (35% crude protein), isolipidic (9% fat) and isoenergetic (15.9 kJ DE-g )1 diets were formulated in which GFM replaced 0.0, 10, 25, 50, 75, 90 and 100% of the protein supplied by HFM. In general, GFM exhibited good potential as a substitute for HFM in red tilapia diets with no adverse effects on growth, feed efficiency, body composition, blood parameters or apparent digestibility of dry matter, protein and gross energy compared with the HFM-based control diet. Growth performance (in terms of final weight, weight gain, per cent increase in weight and growth rate) of fish fed diets containing GFM at 25 or 50% level of replacement for HFM-protein (diets 3 and 4) was statistically higher than for fish fed diets containing GFM at replacement levels >50%. Diet 4 had the best economic efficiency of fish weight gain. Partial or complete substitution of GFM for HFM did not affect feed utilization efficiency (in terms of FCR, FER, PER and APU) or digestibility coefficients of dry matter, protein and gross energy compared with those of the HFM-based diet. Apparent protein digestibility varied little between diets, ranging from 84.2 to 87.3% with no significant differences. Survival of fish fed all the experimental diets (except for fish fed GFM at 90 or 100% level of replacement for HFM-protein) was comparable with that of fish fed the control diet and ranged from 91.7 to 98.3%. KEY WORDS

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Abstract.— Purified diets were formulated and fed to seven groups of Nile tilapia Oreochromis niloricus fingerlings for 12 weeks. Six of the formulated diets contained 5 or 50 mg/kg of ascorbic acid equivalent supplied either by L‐ascorbic acid (AA), L‐ascorbyl‐2‐sulfate (AS) or L‐ascorbyl‐2‐polyphosphate (APP). The seventh basal diet was ascorbate‐free and served as the control. The study indicated that APP or AS was more effectively utilized as a source of vitamin C than equimolar AA in promoting growth, improving food conversion, and preventing scurvy in Nile tilapia. Fish fed the ascorbate‐free diet and the diet containing 5 mg AA/kg exhibited external signs of scurvy at 10 weeks. Diets containing 5 mg/kg of ascorbic acid from AS or APP provided some growth with no overt signs of scurvy indicating that this concentration of AS and APP might be near the minimum requirements for the species. The best growth, food conversion ratio, survival rate, and ascorbic acid content in liver were obtained with the diet containing 50 mg ascorbate equivalent/kg diet from APP followed by the diet containing 50 mg ascorbate equivalent/kg diet from AS. Fish fed diets with 50 mg ascorbic acidkg diet from AS and APP gained 27.9% and 36.2% more weight, respectively, than fish fed diets with 50 mg ascorbic acidkg diet from AA. These results indicated nearly equal ascorbic acid activity from AS and APP.

In an attempt to identify appropriate times for initial application of supplemental feed in polyculture fertilized fish production earthen ponds, a study was conducted for 19 wk to establish the growth performance, yield, survival, and body composition of Nile tilapia, common carp, and silver carp as influenced by four different feeding regimens (treatments). The four treatments were: 1) supplemental feeding beginning at onset of the experiment (T‐I) (control treatment); 2) 6‐wk delay of feeding after fish stocking (T‐II); 3) 13‐wk delay of feeding after fish stocking (T‐III), and 4) no supplemental feed application (T‐IV). Two ponds were assigned to each treatment and each pond was stocked with a similar number and weight of each fish species. A commercial pelleted fish feed (25% protein) was used to feed fish in T‐I, T‐II, and T‐III at 3% of their body weight, twice a day. At the end of the experiment, fish species (except for silver carp) in T‐II showed weight gain, growth rates, and yields significantly higher than fish in T‐III or T‐IV. Also, the total fish production and net profit in T‐II were significantly higher than in T‐III or T‐IV. Fish species in T‐II showed weight gain, growth rates, survival rates, and yields similar to those of T‐I (control treatment) with no significant differences. The amount of feed consumed by fish in T‐II was reduced by approximately 7.3% compared to that consumed by fish at T‐I. Moreover, there was increase in th net profit in T‐II by 4.8% over that achieved in T‐I. Therefore, T‐II appears to be the most appropriate among the tested feeding treatments and recommended for use in order to achieve the best growth, production, and net profit.