N. R. Le François

Dietary protein hydrolysate and trypsin inhibitor effects on digestive capacities and performances during early-stages of spotted wolffish: Suggested mechanisms

Growth rate is dependent upon adequate provision of amino acids especially in newly-hatched fish which experience very high growth rate. The replacement of a fraction of protein content by partially hydrolyzed (pre-digested) proteins was carried out and the digestive capacities and performances of larval/juvenile spotted wolffish (Anarhichas minor) were measured. The goal of this study was to verify whether the scope for growth is principally dictated by the proteolytic capacity of the digestive system by examining the effect of protein hydrolysates (PH) and trypsin inhibitor dietary inclusion on protein digestion/assimilation capacities, growth and survival. Four experimental diets were examined: C (control) I (supplemented with 750 mg/kg soybean trypsin inhibitor (SBTI)) H (supplemented with 20% PH) and HI (supplemented with 20% PH and 750 mg/kg SBTI). Protein hydrolysate supplementation gave significantly higher body mass than control at day 15 post-hatching. Unexpectedly, at day 30 and 60, fish administered diet HI (containing trypsin inhibitor) were heavier than the other groups. Suggested mechanisms are presented and discussed. The main conclusions of this study are that wolffish larval stage lasts roughly 15 days and that juvenile growth is linked to proteolytic capacity, but also very likely to absorption capacity of peptides and amino acids.

EXPOSURES TO LOW-LEVEL IONIZING RADIATION : EFFECTS ON BIOCHEMICAL AND WHOLE-BODY INDICES OF GROWTH IN JUVENILE BROOK CHARR (SALVELINUS FONTINALIS)

Exposure to ionizing radiation (IR) was used to alter gonadal growth in brook charr (Salvelinus fontinalis). To evaluate the possible effects of low-level doses of IR on future seawater adaptability of brook charr, the physiological state and growth performances of juvenile brook charr were examined for 15 months. Four groups of fish were exposed to different experimental doses of IR at the hatching stage: 0 (control), 6.2, 7.8, and 11.4 Gy. Growth in length and weight and condition factors of the irradiated groups were initially impaired compared with the control. Differences in growth were observed and were proportional to the irradiation dose. Initial growth delay in the irradiated groups was followed by compensatory growth of sufficient magnitude and duration that similar weights and lengths among all groups were reached by the end of the growth trial. Changes in the concentration of nucleic acids, protein, and water content were evaluated at three trimestrial intervals in the control and 11.4 Gy groups. DNA content was systematically found to be higher in the irradiated groups compared with the control (602.76 and 850.38 μg/g wet tissue). No difference in protein content (mg/g) in relation to fish weight was found between both groups during the freshwater growth period. Lipid analysis was performed on the final samples and was found to be significantly higher in the irradiated groups displaying catch-up growth (8.2% and 11.4% wet weight). RNA/DNA, RNA/protein, and protein/DNA were also calculated. J. Exp. Zool. 283:315–325, 1999.

Alteration of gonadal development of brook charr (Salvelinusfontinalis): Impact on salinity tolerance following transfer in estuarine conditions

Sexual development of brook charr (Salvelinus fontinalis) was altered using ionizing radiation in order to study the implication of gonad development on salinity tolerance following transfer to estuarine conditions. Four groups of fish at the hatching stage were exposed to different doses of ionizing radiation: 0 (control), 6.2, 7.8, and 11.4 Gray. Prior to the estuarine introductions, the effects of ionizing radiations on mortality and growth of young brook charr reared in freshwater were examined over 19 months. Cumulative mortalities reached a maximum level after 90 days in all groups and did not exceed 20%. Final growth parameters were similar between all experimental groups. Significant sterility rates, were achieved on the female gender. The highest radiation dose resulted in the highest yield of sterile fish (59.5%). Transfer to estuarine conditions in June (period of enhanced osmoregulatory capacities) and in October (period of diminished osmoregulatory capacities) 1994, revealed that all sterile individuals survived the prolonged stay in hyperoosmotic environment during and beyond the spawning season, while the maturing fish suffered high mortality (up to 73.3%). It was found that low-level irradiation exposure had no direct negative effect on the survival capacity of brook charr in estuarine conditions. J. Exp. Zool. 279:273–283, 1997.

Sperm cryoconservation in Anarhichas sp., endangered cold-water aquaculture species with internal fertilization

This study contributes to the identification of an adequate cryopreservation medium for wolffishes sperm (Anarhichas minor and A. lupus). Our results also confirm the presence of antifreeze proteins in the seminal fluid of the Atlantic wolffish (Anarhichas lupus) that could facilitate the process of cryoconservation in association with increased post-thaw motility and fertilization rates. Cryo-Fish, a commercial diluent was the most efficient in our trials, with 80% motility post-thaw.

White muscle 20S proteasome activity is negatively correlated to growth rate at low temperature in the spotted wolffish Anarhichas minor

The effect of temperature and mass on specific growth rate (G) was examined in spotted wolffish Anarhichas minor of different size classes (ranging from 60 to 1500 g) acclimated at different temperatures (4, 8 and 12 degrees C). The relationship between G and 20S proteasome activity in heart ventricle, liver and white muscle tissue was then assessed in fish acclimated at 4 and 12 degrees C to determine if protein degradation via the proteasome pathway could be imposing a limitation on somatic growth. Cardiac 20S proteasome activity was not affected by acclimation temperature nor fish mass and had no correlation with G. Hepatic 20S proteasome activity was higher at 12 degrees C but did not show any relationship with G. Partial correlation analysis showed that white muscle 20S proteasome activity was negatively correlated to G (partial Pearsons r = -0.609) but only at cold acclimation temperature (4 degrees C). It is suggested that acclimation to cold temperature involves compensation of the mitochondrial oxidative capacity which would in turn lead to increased production of oxidatively damaged proteins that are degraded by the proteasome pathway and ultimately negatively affects G at cold temperature.

Digestive capacities, inbreeding and growth capacities in juvenile Arctic charr Salvelinus alpinus

Genetic variation in growth performance was estimated in 26 families from two commercial strains of Arctic charr Salvelinus alpinus. Physiological determinants of growth and metabolic capacities were also assessed through enzymatic assays. A relatedness coefficient was attributed to each family using parental genotypes at seven microsatellite loci. After 15 months of growth, faster growing families had significantly lower relatedness coefficients than slower growing families, suggesting their value as indicators of growth potential. Individual fish that exhibited higher trypsin activity also displayed higher growth rate, suggesting that superior protein digestion capacities can be highly advantageous at early stages. Capacities to use amino acids as expressed by glutamate dehydrogenase (GDH) activities were lower in the liver of fast-growing fish (13-20%), whereas white muscle of fast-growing fish showed higher activities than that of slow-growing fish for amino acid metabolism and aerobic capacity [22-32% increase for citrate synthase (CS), aspartate aminotransferase (AAT) and GDH]. The generally higher glycolytic capacities (PK and LDH) in white muscle of fast-growing fish indicated higher burst swimming capacities and hence better access to food.