Pierre Bergot

Dietary ascorbic acid needs of common carp (Cyprinus carpio) larvae

Abstract As some controversy seem to exist regarding the dietary essentiality of ascorbic acid (AA) for larval cyprinids, a study was conducted to determine the dietary AA requirements with first-feeding larvae of common carp. Six semi-purified diets were formulated to contain graded levels (0, 10, 30, 90, 270, 810 mg kg −1 ) of AA supplied as ascorbyl polyphosphate. Triplicate groups of 250 larvae each were fed one of the experimental diets using automatic feed dispensers over the light hours of the day (temperature: 24±1°C; photoperiod 16L:8D). A duplicate group was kept unfed. Survival, body length and weight increments were recorded. At the end of the 21 day trial, samples were withdrawn for analyses of whole body vitamin C content. The results indicate that common carp larvae have a dietary requirement for ascorbic acid. The required level for maximum tissue storage is higher than that needed for survival and maximum growth. Based on growth performance, a dietary requirement of about 45 mg AA equivalent kg −1 was established. Maximal body vitamin C concentration (104–115 μ g g −1 wet weight) was observed in larvae fed 270 mg AA equivalent kg −1 or more.

Relationship between number of pyloric caeca and growth in rainbow trout (Salmo gairdneri Richardson)

Abstract The relationship between fish length and number of pyloric caeca was studied in fullsib families, with different caeca number, which were obtained through genetic selection and reared in two different hatcheries. At Lees-Athas hatchery a significant positive correlation between caeca number and size of fish of the same age was demonstrated, both within and between families. An influence of rearing conditions upon this relationship was also observed as no significant correlation was found in Donzacq hatchery with the same families. In both hatcheries, families with many caeca exhibited better food conversion ratios than families with fewer caeca, the former showing either lower feed intake for the same growth rate or greater weight gain for the same feed intake. Two non-exclusive hypotheses could account for the growth-caeca number relationship: the caeca number could be either an indicative character reflecting initial growing conditions or a causal character, acting on intestinal morphology and food utilization. In either case, caeca number seems to be an interesting criterion in trout selection.

Lipid supplementation of casein-based purified diets for carp (Cyprinus carpio L.) larvae

Abstract Common carp larvae were fed artificial diets based on purified ingredients (casein, casein sodium salt, casein hydrolysate, dextrin, vitamin and mineral premixes). Eight experimental diets containing two levels of peanut oil (3 or 4.5%) and supplemented with graded levels of cod liver oil (0, 1, 2 or 4%) with or without phospholipids (0 or 2%) were fed to duplicate groups for 28 days. A yeast-based diet served as the control. Survival (from 10 days onwards) and growth (as early as day 7) were significantly improved by phospholipid supplementation. By day 21, larvae fed diets without phospholipids exhibited low survival rates (17–22%) and low mean weights (90–130 mg) compared to larvae fed phospholipid-supplemented diets (survival 53–83%, mean weight 180–200 mg). Daily mortality was low in all groups between day 21 and day 28. By day 28, the best casein-based diet resulted in a lower survival rate than the yeast-based control diet (78 vs. 90%). However, it supported a higher mean larval weight (550 vs. 330 mg). In contrast to phospholipid, dietary cod liver oil level had little effect on early survival and growth of the larvae. An increase in dietary cod liver oil resulted in marked changes in fatty acid composition of carp total lipid by day 28: i.e., n −3 fatty acids increased; 20:4 n −6, 20:5 n −6 and 20:3 n −9 decreased, and 22:3 n −9 and 22:4 n −9 disappeared. First-feeding carp larvae were able to utilize semi-purified diets better than previously reported. During the first 2 weeks, dietary phospholipid supply seemed more critical for early larval survival and growth than a supply of n −3 fatty acids from cod liver oil.

Alimentation artificielle des larves de carpe (Cyprinus carpio L.)

Abstract A batch of 12 000 carp larvae ( Cyprinus carpio L.) issued from a single couple of breeders was reared for 43 days exclusively using artificial food (for 21 days on a diet based mainly on liver and yeast, and on a commercial trout starter feed during the following period). After 24 days of rearing in a tank of 300 l, survival was 87%. After 19 additional days of rearing in a tank of 1500 l, survival was 71% and mean weight 1.16 g. The daily specific growth rate decreased from 23% to 8% during the experiment. Total food conversion ratio was 0.62 (6.08 kg of food was distributed for a final total weight of 9.88 kg of fish). The results presented here indicate that it is possible to rear carp larvae without zooplankton. Exact determination, in the course of rearing, of the total weight of fish and precise adjustment of the quantities of food delivered should allow further improvements in survival and growth.

Supplementation of artificial diets for common carp (Cyprinus carpio L.) larvae

Abstract Duplicate groups of full-sib carp (Cyprinus carpio L.) larvae were reared at 24±0.5°C and fed six artificial diets (A to F) with the same protein sources (yeast powder 59%; dry beef liver 41%) and a diet (G) in which half of the protein source was replaced by egg powder. Diets were supplemented with different levels (0%, 5% or 10%) of cod liver oil (CLO), mineral premix (M) and vitamin premix (V). After 21 days on experimental diets (D0–D21), larvae were fed a commercial feed for 10 additional days (D21–D31). On day 21, survival of larvae fed the yeast-liver diet supplemented with CLO (5%), M (5%) and V (5%) (diet A) was 64% and mean body weight was 169 mg. Compared to diet A, diet B (CLO 10%, M 10%, V 10%) did not improve survival (68%) or mean body weight (170 mg). Larvae fed a non-supplemented diet (C) containing only yeast and liver had a lower survival rate (42%) and mean body weight (63 mg). Vitamins appeared to be a limiting factor as the larvae fed diet D with CLO 5%, M 5% and no V exhibited a very low survival rate (13%) and mean body weight (28 mg). The mineral premix also seemed necessary as results obtained with diet E (CLO 5%, V 5%, no M) were similar (survival 52%, mean weight 53 mg) to those obtained with the non-supplemented diet (C). Diet F (M 5%, V 5%, no CLO) led to an excellent survival rate (95%) and mean body weight of 189 mg on day 21. Larvae fed diet G (42.5% yeast-liver mixture, 42.5% egg powder, 5% CLO, 5% M, 5% V) reached an individual mean weight of 140 mg. It was concluded that the mineral and vitamin supplementation of the yeast-liver diets was necessary, whilst an addition of 5% CLO in these diets had a negative effect. Survival of larvae initially fed the best diet (F) was 95% and mean body weight was 755 mg after 10 additional days of feeding (D21–D31) a commercial diet. This confirmed the possibility of rearing carp larvae on artificial food with high survival and growth rates.

Effect of selecting sires according to their number of pyloric caeca upon the growth of offspring in rainbow trout (Salmo gairdneri Richardson)

Abstract Two sires were selected, from each of four full-sib families, according to high (“sup”) and low (“inf”) caeca number. Pyloric caeca number, precocity and growth of offspring were studied in a factorial breeding plan of these eight sires crossbred with three dams. Compared with the progeny of sires “inf”, the progeny of sires “sup” exhibited (a) a higher caeca number, (b) slightly more precocious development (as shown by beginning of hatching, first feeding and degree of hydration during yolk resorption) and (c) a higher growth rate. Significant correlations were found, within dams, between fish length at 239 days and caeca number both within and between families of offspring. Although the physiological links between caeca number and growth are still obscure, the possibility of improving growth performance in rainbow trout by indirect selection on caeca number is discussed.