|Rawles, Steven - Steve|
Submitted to: Journal of the World Aquaculture Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/6/2009
Publication Date: 5/1/2010
Citation: Rawles, S.D., Gaylord, T.G., Snyder, G.S., Freeman, D.W. 2010. The influence of protein and energy density in commercial diets on growth, body composition, and nutrient retention of sunshine bass Morone chrysops x Morone saxatilis reared at extreme temperature. Journal of the World Aquaculture Society. 41:165-178. Interpretive Summary: It typically takes 18 months to raise hybrid striped bass to market size when producers typically stock fingerlings from June to September. This requires over-wintering fish in ponds, and feeding during the hot months of the following summer in order to achieve market size by the end of the second fall after stocking. During winter, pond temperatures often dip below 15C (60F), where feeding typically slows down or stops. Hybrid striped bass are hybrids of temperate zone species and field reports suggest that feeding continues at lower temperatures than those reported for other warmwater fish like catfish or tilapia, but the minimum feeding temperature is unknown. Sometimes warmer weather in winters of the southeast U.S. allows producers to feed sporadically to maintain fish health, and to improve growth. Other producers stock-pile fingerlings in cool water to ensure a year-round supply. In all these cases, there are great losses of fish due to disease, cannibalism, and poor water quality because feeding is sporadic, uneaten feed decomposes and decays water quality, and fish are stressed. During the summer, on the other hand, pond temperatures in the south often exceed optimum for raising hybrid striped bass. Because fish metabolism and passage through the digestive system increases with water temperature, diet assimilation in summer is less efficient in hybrid striped bass and more protein is wasted into the pond. This also degrades water quality during the most stressful period of production. Research is lacking regarding optimum diets for feeding hybrid striped bass in winter and midsummer. Therefore, three growth trials were conducted with juvenile sunshine bass to determine if there was an advantage to feeding a commercial high-protein/high-fat diet during winter and a low-protein/high fat diet during summer. In the first trial, two commercially extruded, practical diets (40% protein/10% lipid vs. 48/18) were fed to fish held in variable cool water 8-20C (46-68F) or constant 26C (80F) water for 14 wks. Temperatures in the cool water tanks were chosen to simulate winter-spring conditions. In the second and third trials, experiments were conducted in which four commercial diets (35/10, 35/15, 40/10 and 40/15) were fed to to fish held at 29C (84F) or 32C (90F) for 4 wks to simulate near optimum vs. extreme summer water temperatures. At 8C (46F), minimal feeding was observed and fish lost weight. Fish consumed feed and gained weight at 10C (50F) or above. In all trials, liver size was a sensitive indicator of the culture temperature as well as the appropriateness of the tested protein and fat levels in the diets. Feed consumption, feed efficiency, fillet weight, body fat, liver size, and protein and energy retention were affected by the water temperature as well as the protein and energy levels in the test diets. Results suggest that careful feeding of nutrient dense diets when temperatures are above 15C will improve production efficiency. In addition, hybrid striped bass showed remarkable adaptation to extremely high culture temperature.
Technical Abstract: Three growth trials were conducted with juvenile sunshine bass reared at temperatures typical of winter or summer pond culture in the Southeastern United States. The trials were designed to determine if there was an advantage to feeding a commercial high-protein/high-fat diet during winter and a low-protein/high fat diet during summer. In the first trial, two commercially extruded, practical diets (40% protein/10% lipid vs. 48/18) were fed to apparent satiation to fish held in variable cool water (8-20 C) or constant 26 C water for 14 wks. Temperatures in the cool water (8-20 C) tanks were chosen to simulate winter-spring conditions. In the second and third trials, factorial experiments were conducted in which four commercial diets (35/10, 35/15, 40/10 and 40/15) were fed to apparent satiation to fish held at 29 C or 32 C for 4 wks to simulate near optimal vs. extreme summer water temperatures. At 8 C, minimal feeding (0.3 % of body weight per d) was observed and fish lost weight. Fish consumed feed daily and gained weight at 10 C or above. At 8-20 C, intake of the 48/18 diet was less than that of the 40/10 diet only when water temperature was above 15 C; however, gain was not different. At 26 C, fish consumed less of the 48/18 diet for greater gain than fish consuming the 40/10 diet. At 8-20 C, feed efficiencies increased with temperature and diet protein/lipid level. Visceral and whole-body fat tended to be diet- but not temperature-dependent and averaged 4% higher in fish fed the 48/18 diet. Muscle ratio and whole-body protein retention were temperature- but not diet-dependent. Energy retention was positively related to both temperature and diet nutrient density. At 29 and 32 C (summer culture trials), daily gain and final fish weight were positively related to protein but not lipid level in the diet. At 29 C, fish consumed less 35% protein diet than 40% protein diet regardless of dietary fat level; whereas, consumption did not differ among diets at 32 C. Feed efficiencies were positively related to both dietary protein and lipid level at 29 and 32 C. The effects of diet nutrient density on fat versus muscle content, and energy and protein retention differed at 29 C and 32 C. Intraperitoneal fat (IPF) appeared unaffected by diet at 29 C; whereas, muscle ratio was higher at the higher protein level (40%). At 32 C, IPF was positively related to dietary protein and fat; whereas, muscle ratio was unaffected by diet. At 29 C, both energy and protein retention appeared unrelated to diet; whereas at 32 C, energy retention was positively related to dietary fat level and protein retention was positively related to both protein and fat level in the diet. In all trials, liver size (hepatosomatic index) was a sensitive indicator of culture temperature and dietary protein and fat levels. Livers from fish held in cool water were larger than those from fish held at 26 C, and fish fed diets of lower nutrient density had larger livers than fish fed diets of higher nutrient density, regardless of culture temperature. Hybrid striped bass showed remarkable adaptation to extremely high culture temperature and results suggest that judicious feeding of nutrient dense diets when temperatures are above 15 C will improve production efficiency.