Carbohydrate utilization in striped bass (Morone saxatilis) and sunshine bass (M-chrysops female x M-saxatilis male)
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abstract
An 8-week feeding trial to determine the effects of carbohydrate complexity on growth and body composition of advanced striped bass and sunshine bass fingerlings (80-85 g, initial weight) was followed by a digestibility trial to determine the effects on apparent digestibility coefficients (ADCs). Fish were fed semi-purified, isonitrogenous (35% crude protein), isolipidic (5%) diets containing either no soluble carbohydrate or glucose, maltose, or dextrin at 25% of diet. Weight gain and feed efficiency of sunshine bass was significantly greater than that of striped bass regardless of dietary treatment. Weight gain and feed efficiency of sunshine bass increased with decreasing molecular weight of dietary carbohydrate whereas only dextrin inclusion significantly increased (P < 0.05) striped bass weight gain. Feed efficiency of striped bass was unaffected by the kind of soluble carbohydrate included in the diet. Inclusion of soluble carbohydrate produced greater body fat deposition and hepatosomatic index (HSI) values in fish compared to those fed the basal diet. Carbohydrate complexity had no apparent effect on any of the body composition indices. Sunshine bass exhibited the largest HSI values while striped bass exhibited the greatest muscle ratio values. Dry matter and ash contents of the liver were higher in striped bass whereas liver glycogen levels were markedly higher in the sunshine bass. Liver dry matter increased in sunshine bass but decreased in striped bass when soluble carbohydrate was included in the diet. Striped bass and sunshine bass fed diets containing glucose or dextrin had lower liver protein and lipid values than fish fed the diet containing maltose or the basal diet. In contrast, fish fed diets containing glucose or dextrin had higher liver glycogen values than fish fed the diet containing maltose or the basal diet. These data suggest that both striped bass and sunshine bass are able to utilize up to 25% dietary polysaccharide in the diet whereas maltose may not be used as efficiently at this inclusion level. Dietary glucose significantly depressed protein ADC in sunshine bass but there was no discernable effect of carbohydrate complexity on protein digestibility in striped bass. Lipid ADC was similar among the dietary treatments but significantly higher in sunshine bass. Digestibility of diet energy was lower in fish fed the basal diet (0% soluble carbohydrate) but was similar among the different kinds of soluble carbohydrate. Digestible energy (DE) values of glucose, maltose, and dextrin were 2.74, 2.38, and 1.73 kcal/g, respectively, for sunshine bass and 3.54, 3.49, and 2.20 kcal/g, respectively, for striped bass.
