Response of sunshine bass (Morone chrysops x M. saxatilis) to digestible protein/dietary lipid density and ration size at summer culture temperatures in the Southern United States

Authors: Rawles, Steven - Steve; Green, Bartholomew - Bart; GAYLORD, GIBSON - Us Fish And Wildlife Service; Barrows, Frederic; McEntire, Matthew - Matt; Freeman, Donald

Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/22/2012
Publication Date: 7/2/2012
Citation: Rawles, S.D., Green, B.W., Gaylord, G., Barrows, F., McEntire, M.E., Freeman, D.W. 2012. Response of sunshine bass (Morone chrysops x M. saxatilis) to digestible protein/dietary lipid density and ration size at summer culture temperatures in the Southern United States. Aquaculture. 356-357:80-90.

Interpretive Summary: Temperature and ammonia levels often increase dramatically in ponds during summer production of hybrid striped bass. Summer temperatures are also projected to increase in the Southern U.S. Ammonia is the primary waste product that fish excrete into the pond from the protein in the feed that they consume. Long periods of high ammonia in the summer can become toxic and cause fish stress, disease, and death. Producers will stop feeding or they will try to feed diets with lower protein in order to reduce ammonia in ponds. However, this practice means days of feeding are lost and fish production is lower. There is little data to guide producers toward the best feeding strategy or the optimum diet that will maximize production and minimize wastes into the pond during summer. We tested six diets that varied in digestible protein level from 33% to 47% and contained either 10% or 18% fat. We fed the diets to hybrid striped bass held in tanks at a constant high temperature that mimicked summer conditions in ponds. Half the tanks of fish received as much of their particular test diet as they would eat for four months. The other half were fed 20% less of the same test diets. At the end of the experiment, the diet that both maximized growth and retention of nutrients from the diet and minimized ammonia waste was the diet containing 40% digestible protein and 18% fat regardless of how much diet was fed. This information will help hybrid striped bass producers become more efficient at managing feeding and pond water quality during summer.

Technical Abstract: Temperature and ammonia levels often increase dramatically in ponds during summer production of sunshine bass and summer temperatures are projected to increase in the Southern US. Extended periods of high ammonia result in fish stress, disease, mortality and significant loss of feeding days as producers attempt to reduce ammonia to manageable levels through reduced feeding or lower protein diets. A factorial feeding trial was conducted in temperature controlled tanks to investigate main and interactive effects of three digestible protein (DP) levels (33, 40, 47%), two lipid levels (10, 18 %) and two ration levels (full fed: satiation, restricted: 80% of satiation) on growth, body composition, nutrient and amino acid retention, and ammonia and phosphorus excretion in sunshine bass (mean weight:75g) reared at elevated temperature (30.5 +/- 0.5ºC) . Diets were balanced on an available amino acid basis to the profile of hybrid striped bass muscle and supplemented with lysine and methionine at the equivalent of 330, 400, or 470 g/ kg of muscle protein. Each DP x lipid x ration treatment was fed to triplicate tanks of fish for 116 days. All measured responses were significantly altered by main and interactive effects, but the patterns of interactions were similar among responses. Restricted feeding resulted in much lower final weights and weight gains but much higher ammonia excretion as a function of feed or N fed and body weight (BW), regardless of DP level. Lower dietary fat (10%) resulted in lower weight gains and poorer feed conversions as well as higher ammonia excretion (per g N fed/kg BW) regardless of DP or ration level. Weight gain (475%) and final fish weight (434 g) were highest at 47% DP/18% dietary lipid, but feed conversion, protein, energy and amino acid retention efficiencies were markedly poorer in the 47% DP diets regardless of lipid level due to hyperphagia in fish fed this diet. The 40/18 diet consistently outperformed the 33/18 diet in better growth and lower ammonia excretion as a function of N fed/ BW, and nearly equaled the growth attained by fish fed 47/18 diet. Increasing ration to satiation at elevated temperature resulted in much greater improvements in weight gain, final weight and lower ammonia excretion of fish fed the 40/18 diet, as opposed to those fed the 33/18 or 47/18 diets. Amino acid retentions were nearly equal between the 33/18 and 40/18 diets and restricting feed to 80% of satiation slightly improved feed conversions and protein and amino acid retentions. Consistent lipid x DP interactions generally indicated that the differences among responses to DP level seen at 18% dietary lipid significantly decreased or disappeared at 10% dietary lipid. Phosphorus excretion was low and not significantly altered by main effects. Results suggest that a producer desiring to reduce pond ammonia with the least compromise to production efficiency would be better served by feeding a 40% DP/ 18% lipid diet at a reduced level instead switching to a lower protein diet.