Karl D. Shearer

Factors affecting the proximate composition of cultured fishes with emphasis on salmonids

Abstract The endogenous and exogenous factors reported to affect the proximate composition of cultured fishes, with emphasis on salmonids, are examined. Methods of reporting and comparing proximate composition are discussed. Examination of measurements presented in a number of published papers, using allometric analysis, indicates that comparison of proximate compositions on a dry weight basis and failure to include fish size as a covariate have, in many cases, led to erroneous conclusions concerning the effects of environmental and dietary factors on the proximate composition of cultured fishes. Available evidence indicates that the protein content of growing salmonids is determined solely by fish size (is endogenously controlled), that lipid level is effected by both endogenous and exogenous factors, that ash content is homeostatically controlled, and that whole body moisture is inversely related to body lipid. The implications of the present findings to nutrition studies and the potential for modification of carcass composition in cultured fish are discussed.

Effects of ration on somatotropic hormones and growth in coho salmon.

We examined the response of growth hormone (GH), total plasma insulin-like growth-factor I (IGF-I), and growth rate to a change in ration in coho salmon. Tanks of individually tagged fish were placed on high, medium, or low ration, and sampled every 2 weeks for 8 weeks to create a range of growth rates. Some fish received non-lethal blood draws, while others were sampled terminally. Plasma IGF-I levels were higher in high ration fish than in low ration fish from 4 weeks after the beginning of experimental diets to the end of the experiment. GH levels were low and similar in all fish after changing rations, except for the fish in the low ration group at week 2. IGF-I was strongly correlated with specific growth rate in weight in terminally sampled fish after 4 weeks. GH did not correlate with growth rate or IGF-I levels. Growth parameters (length, weight, specific growth rates in weight and length, and condition factor) responded to ration. Serial sampling reduced growth rates and hematocrit, but did not change hormone levels. This study shows that IGF-I responds to changed rations within 2-4 weeks in salmonids.

The use of factorial modeling to determine the dietary requirements for essential elements in fishes

Abstract A factorial model is used to examine the relationship between the net requirement for an essential element in fish (the amount required for growth and replacement of endogenous loss) and the dietary concentration necessary to meet that requirement. Factors that affect the dietary requirement (C), when stated as a concentration in the diet, are: the bioavailability of the element (A), feed intake (F), the amount of the element taken up from the water (U), the requirement for new tissue synthesis (G) and the amount of endogenous loss (E). The model contains factors that can be empirically quantified but the relationships among these factors are determined deductively according to the equation C = [(G + E − U)/A]/F. Examples, using both real and hypothetical data, demonstrate how quantification of these factors and their incorporation into a factorial model will allow broader application of the currently available, empirically derived requirements.

Whole body magnesium concentration as an indicator of magnesium status in rainbow trout (Salmo gairdneri)

Whole body magnesium concentrations were found to reflect the magnesium status of juvenile rainbow trout (Salmo gairdneri) fed semi-purified diets containing graded levels of magnesium (36–2120 mg/kg diet). Low whole body concentrations (<300 mg/kg wet basis) preceded growth reduction or other signs of clinical deficiency. Whole body concentrations greater than 370 mg/kg were indicative of magnesium sufficiency. Trout met a considerable portion of their requirement by direct uptake from the environment in fresh water containing a low level of magnesium (1.3 mg/l). Analysis of growth and whole body Mg concentration data using analysis of variance suggests that trout require about 0.06% of their diet as Mg. Analysis of the same data using dose-response curves indicates an optimum dietary Mg level near 0.14% of the diet.

Phosphorus Deficiency in Rainbow Trout Fed a Diet Containing Deboned Fillet Scrap

Abstract Whole Pacific hake (Merluccius productus) and hake fillet scrap were ground, heated to accelerate enzymatic hydrolysis, and acidified to prevent microbial degradation. Half of the fillet scrap was screened to reduce the bone content of the product. After 10 d of storage, the liquefied products were combined with feather meal and dried. The dried products replaced fish meal in practical diets, which were fed to rainbow trout (Salmo gairdneri) for 22 weeks. Significant reductions in plasma phosphorus and whole-body and vertebral calcium, phosphorus, and magnesium concentrations were found in rainbow trout fed the diet containing the deboned fillet scrap, while fish fed a phosphorus-supplemented diet had levels similar to fish fed the diets containing whole fish. Plasma alkaline phosphatase activity was unaffected by diet. Rainbow trout fed a diet containing unscreened fillet scrap were similar in all respects to fish fed a diet containing whole fish. This study shows that the high dietary ash prese...

Dietary potassium requirement of juvenile chinook salmon

Abstract Juvenile chinook salmon ( Oncorhynchus tshawytscha ) were fed casein-gelatin-based diets containing graded levels of potassium (0.01–1.20%) for 10 weeks to determine their dietary potassium requirement. The fish were able to sequester potassium directly from the water but they were unable to meet their requirement without additional dietary potassium. Signs of potassium deficiency included anorexia, convulsions, tetany, and death. Although the potassium levels were not replicated in this study, growth-response data suggest that a dietary potassium concentration of 0.8% should produce maximum growth. Whole body potassium saturation (3200 ppm wet fish weight) occurred at a dietary potassium concentration between 0.6 and 1.2% of the diet. Whole body sodium and magnesium were significantly elevated in fish fed potassium-deficient diets.

Effects of various feed supplements containing fish protein hydrolysate or fish processing by-products on the innate immune functions of juvenile coho salmon (Oncorhynchus kisutch)

Abstract Immunomodulators administered to fish in the diet have been shown in some cases to enhance innate immune defense mechanisms. Recent studies have suggested that polypeptide fractions found in fish protein hydrolysates may stimulate factors in fish important for disease resistance. For the current study, groups of coho salmon were reared on practical feeds that contained either fish meal (Control diet), fish meal supplemented with cooked fish by-products, or fish meal supplemented with hydrolyzed fish protein alone, or with hydrolyzed fish protein and processed fish bones. For each diet group, three replicate tanks of fish were fed the experimental diets for 6 weeks. Morphometric measurements, and serologic and cellular assays were used to evaluate the general health and immunocompetence of fish in the various feed groups. Whereas the experimental diets had no effect on the morphometric and cellular measurements, fish fed cooked by-products had increased leucocrit levels and lower hematocrit levels than fish from the other feed groups. Innate cellular responses were increased in all feed groups after feeding the four experimental diets compared with pre-feed results. Subgroups of fish from each diet group were also challenged with Vibrio anguillarum (ca. 7.71×10 5 bacteria ml −1 ) at 15 °C by immersion. No differences were found in survival among the various feed groups.

Zinc Supplementation of Trout Diets: Tissue Indicators of Body Zinc Status

Abstract Rainbow trout (Salmo gairdneri) were fed one of three different diets, based either on fish meal, soybean meal, or egg white, containing varying levels of zinc. Several fish tissues were analyzed for zinc content after 202 d to determine if any tissue was a sensitive indicator of zinc status. Caudal fin and whole-body zinc levels of the fish were found to reflect the dietary levels of zinc. We observed a strong statistical correlation between whole-body zinc levels and the zinc concentration of the caudal fin (r = 0.89; P < 0.01). At the same time, we observed a negative correlation between whole-body iron concentration and whole-body zinc levels (r = 0.87; P < 0.01). A strong negative correlation also was observed between dietary zinc and whole-body iron (r = 0.95; P < 0.001). Our data indicate that caudal fin zinc concentrations are a good indicator of zinc status.

Effects of ration level on immune functions in chinook salmon (Oncorhynchus tshawytscha)

The relationship between nutritional status and disease resistance in cultured salmonids can be affected by dietary manipulations. Careful attention to feeding levels may be important to avoid imbalances in nutrient levels that could ultimately impair a fishs ability to resist infectious microorganisms. In the current study, fish in three feed-level groups were fed an experimental diet either to satiation, 64% of satiation or 40% of satiation. A fourth group of fish were fed a commercial diet at the 64% of satiation level and served as controls. To evaluate certain indices of disease resistance in the test and control fish, a panel of assays was employed to measure humoral and cellular immune functions 30, 39 and 54 weeks after starting the dietary treatments. The panel included measures of blood hematocrit and leucocrit levels, plasma protein concentration and serum lysozyme and complement activity. Cellular analyses included differential blood leucocyte counts, NBT reduction and phagocytosis by pronephros macrophages and myeloperoxidase activity of pronephros neutrophils. No differences were observed in those indices between fish tested from the control-diet group (commercial diet fed at the 64% rate) and fish tested from the 64% feed-level group, except that fish fed the commercial diet had a greater concentration of plasma protein. Leucocrit values and plasma protein concentrations tended to increase among the experimental feed groups as the ration increased from 40% to satiation. More importantly, phagocytic activity by anterior kidney leucocytes was found to be inversely proportional to the feed level. Whereas the results of this study provide evidence that the salmonid immune system may be fairly robust with regard to available metabolic energy, the significant changes observed in phagocytic cell activity suggest that some cellular immune functions may be affected by the feed level.

Relationship of insulin-like growth factor-I and insulin to size and adiposity of under-yearling chinook salmon.

Sub-yearling spring chinook salmon were fed either a LoFat or HiFat diet from February to November. Fish were sampled over 2 days in November, following 24- and 48-h fasts. Length vs. weight relationships between fish fed the two diets were similar; however, fish fed the HiFat diet had roughly twice the body lipid as fish fed the LoFat diet (9% vs. 4.5%, respectively). Plasma IGF-I vs. length relations between fish fed the two diets were similar; overall, there was a strong relation between plasma IGF-I and length (r(2)=0.53). Similarly, plasma log (insulin) vs. length relations did not vary between the two diets; however, the relationship of log (insulin) vs. length was weak (r(2)=0.2). There was little or no relationship between plasma IGF-I or log (insulin) and body adiposity. Finally, there was a weak relationship between plasma IGF-I and log (insulin) (r(2)=0.23).