Carbohydrates (CH) are not essential nutrients for fish, but they are a low-cost energy source and are commonly used in the formulation of extruded diets. Additionally, certain CH can be used as an energy source effecting a protein-sparing effect, sparing protein for growth. However, CH can negatively affect fish metabolism, particularly for carnivorous fish. Fish utilization depends on feeding habits, inclusion level and chemical structure of the CH. Striped bass, Morone saxatilis, is an anadromous fish of great commercial interest. Baja California, México is the only world region where this species is reared in seawater. However, culture conditions are not optimal, with lower water temperatures resulting in slower growth. Consequently, there is a need to optimized diets to improve growth and reduce costs.
In the present study, four carbohydrate types (i.e., cellulose, dextrin, raw and gelatinized starch) were evaluated, included at 19% in isoproteic and isolipidic diets. The feeding-trial lasted 60 days with juvenile striped bass of 16-18g initial weight distributed in 24 tanks in a recirculating system and cultured at either 16 or 21 °C in full seawater. At the end of the trial, growth performance, digestive enzyme activity, nutrient digestibility, glycogen and lipid content of the liver, and changes in the intestinal microbiota were assessed.
Temperature significantly affected growth performance, feed efficiency, and digestive enzymes, resulting in higher values at 21°C. Dextrin, the simplest carbohydrate, had adverse effects on fish performance while starch resulted in better utilization. Fish feed the dextrin diet showed an increase in amylase activity, highest diet digestibility, but resulted in lower growth and accumulation of liver glycogen. Striped bass appears to better utilize starch compared to simpler CH. Data with respect to gut microbiota will be presented to aid in elucidating our results.