Amino acid composition of Arctic charr, Salvelinus alpinus (L.) and the prediction of dietary requirements for essential amino acids

Embryo somatic tissues, non‐somatic yolk‐sac materials, and whole, individual fingerlings (age 0+) of Arctic charr, Salvelinus alpinus (L.), as well as a commercial trout diet, were analysed for a wide spectrum of amino acids. Analytical material consisted of prefeeding swim‐up fry that were separated into discrete yolk sac and somatic embryo tissue samples. Amino acid concentrations in fry somatic tissue and whole fingerlings were generally very similar to each other, but were lower than those measured in yolk materials. Higher correlations were observed between the majority of specific amino acid concentrations in the trout diet when compared with fingerling data (r² = 0.91) and fry somatic tissue data (r² = 0.89), than when correlated with fry yolk sac material (r² = 0.76). These results indicate that the essential amino acid profiles of fry somatic tissue and whole fingerlings are closer to that of a commercial feed than they are to the endogenous profiles found in the embryonic yolk sac material itself. The dietary ratios of individual essential amino acids were also compared with the total essential amino acid concentrations (A/E ratios) in whole fingerling tissues, and these ratios could be used to accurately estimate the apparent essential amino acid requirements of Arctic charr. The rationale for using carcass amino acid composition data to estimate the dietary essential amino acid requirements of Arctic charr is discussed.     

Effect of oxidized fish oil, vitamin E and ethoxyquin on the histopathology and haematology of rainbow trout, Salmo gairdneri Richardson

Abstract. Rainbow trout were fed for 24 weeks on practical diets containing varying concentrations of oxidized fish oil, with or without supplementation of vitamin E and ethoxyquin. Serum biochemistry, haematology and histopathology were investigated to measure the relative protection offered by vitamin E (DL–α–toco–pherol acetate) and/or a synthetic substitute (ethoxyquin), against highly or extremely oxidized oil with peroxide values of 120 or 314mEq/kg oil respectively. Groups fed highly or extremely oxidized oils without DL–α–tocopherol acetate supplementation, and with or without supplemental ethoxyquin, exhibited lower red blood cell numbers, haemoglobin content, haematocrit, and increased haemolysis. In addition, fish from these groups had increased, abnormally developing polychromatocytes, splenic haemosiderosis and hepatic ceroidosis. The results indicate that vitamin E protects better and at lower concentrations than does ethoxyquin, and that supplementation with 33 mg of DL–α–tocopherol acetate/kg is adequate to prevent vitamin E deficiency signs when feeding practical diets containing 7.5 % of a highly oxidized oil. Supplementation with ethoxyquin alone to diets containing highly oxidized oil appeared to exert partial protection, but did not increase the level of protection when added simultaneously with DL–α–tocopherol acetate. The data support the theory of a general antioxidant function for vitamin E, and suggest that mortalities ensuing from vitamin E deficiency are due to the cumulative effects of liver dysfunction and anaemia.     

Dietary methionine requirement of juvenile Arctic charr Salvelinus alpinus (L.)

The dietary methionine requirement of juvenile Arctic charr Salvelinus alpinus (L.) was assessed by feeding diets supplemented with graded levels of DL-methionine (9, 12, 15, 18, 21, and 24 g kg⁻¹dietary protein) for 16 weeks at 12°C. All diets contained 400 g kg⁻¹ protein, 170 g kg⁻¹ lipid, 66 g kg⁻¹ ash and an estimated 17.5 MJ digestible energy (DE) kg⁻¹. When live-weight gain was examined using quadratic regression, the estimate of methionine requirement for optimal growth was 17.6 g kg⁻¹ of dietary protein (DP) or 7 g kg⁻¹ of the diet. Requirements estimated on the basis of carcass protein and energy gains were 18.8 and 17.9 g kg⁻¹ DP, respectively. Plasma methionine concentrations and ocular focal length variability measurements did not provide a sensitive measure of requirement, because each responded in a linear fashion to increasing dietary methionine levels. Based on the prevalence of cataracts, the methionine level required to prevent lens pathology (26.7 g kg⁻¹ DP) appears to be higher than that required for maximum growth.     

Patterns of growth and nutrient deposition in lake trout (Salvelinus namaycush), brook trout (Salvelinus fontinalis) and their hybrid, F1 splake (Salvelinus namaycush × Salvelinus fontinalis) as a function of water temperature

Several fish species of the genus Salvelinus are used for stocking freshwaters in North and South America and much of Europe but there is little information about their growth and carcass composition. Lake trout (S. namaycush), brook trout (S. fontinalis) and their hybrid F₁ splake (S. namaycush × S. fontinalis) (initial body weight ca. 2–4 g) were raised at 6.4, 10.6 and 14.9 °C to examine growth and nutrient deposition as a function of water temperature. In all species, weight gain and feed intake increased significantly with water temperature and feed efficiency was significantly lower at 6.4 than at 10.6 and 14.9 °C. In brook trout, Thermal‐unit Growth Coefficient (TGC) growth rate was significantly lower at 6.4 than at 10.6 and 14.9 °C, while in F₁ splake TGC was only lower at 6.4 than 10.6 °C. Expressed in terms of relative composition a significant effect of temperature was observed. In all species, moisture content decreased while crude protein, lipid, ash and energy contents increased with increased temperature. Expressed in absolute terms, however, a significant effect of temperature was not observed. In all species carcass contents increased significantly with increased live body weight and were best described by simple linear equations. Gross energy concentration was significantly affected by both water temperature and body weight. These data indicate that the growth of these species is a function of water temperature and, in absolute terms, carcass composition is mainly a function of body weight and not water temperature. Also, such simple linear equations bode well for modification of existing feed requirement and waste outputs models; improving their applicability to these species.     

Histological effects of the inert suspended clay kaolin on the gills of juvenile rainbow trout, Salmo gairdneri Richardson

Abstract. Juvenile rainbow trout were exposed to 36, 171, 1017 and 4887 mg/1 of suspended kaolin clay for 64 days. Gills were analysed qualitatively and quantitatively using histology. Branchial pathology was absent at all sample times in fish exposed to 36, 171 and 1017 mg/1 kaolin, although intracellular kaolin was visible within filament and lamellar epithelium in gills exposed to 171, 1017 and 4887 mg/1 kaolin at 4, 8, 16, 32 and 64 days. Lesions were found in gills exposed to 4887 mg/1 kaolin at 16 and 32 days but the marked lamellar proliferation was associated with moderate to large numbers of protozoa identified as Ichthyobodo necator . Gills regained normal architecture by 64 days despite continued exposure to kaolin. It is suggested that while the gill lesions were probably a direct result of protozoan infection, kaolin was indirectly responsible for creating a favourable environment for protozoan colonization. The recovery of normal architecture and reduction of protozoan numbers between 32 and 64 days was probably a function of increased mucus secretion, immune response and turnover of branchial epithelium. The authors conclude that exposure to prevailing levels of this inert clay particle, even for periods as long as 64 days, probably has little direct effect on gill structure at the light microscope level. The action of non-inert and organic particles remains to be investigated.     

Optimal protein requirements of young Arctic charr (Salvelinus alpinus) fed practical diets

Young Arctic charr, Salvelinus alpinus (L.), mean weight 2.56 ± 0.02 g, were fed nine isoenergetic (?16.6 MJ digestible energy (DE) kg^?1) practical diets formulated to supply digestible crude protein (DCP) at 40g kg^?1 increments from 230 to 550g kg^?1, for 84 days. Mean weight gain (MWG) and specific growth rate (SGR) were determined every 14 days while carcass composition was determined at the start and end of the experiment. Growth responses attained the highest values in the fish fed the diet with 350 g kg^?1 DCP. Carcass moisture gain, protein gain and apparent net lipid accumulation increased as DCP levels increased to a maximum at 350 g kg^?1 after which there were no differences among treatments. Total carcass lipid and lipid gain decreased as dietary DCP increased up to 470 g kg^?1 with no differences thereafter. Apparent net protein accretion decreased with increasing DCP levels up to 350 g kg^?1 after which there were few differences among treaments. Protein requirements were estimated by fitting MWG and SGR data to broken line regression, quadratic and saturation kinetics models. Results from these analyses suggest that dietary DCP should be provided at between 340 and 392 g kg^?1 (equivalent to ?370 and 420g kg^?1 crude protein) for optimal growth of young Arctic charr reared in similar conditions.