Date of Award

1986

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Fisheries, Animal and Veterinary Science

First Advisor

Lewis T. Smith

Abstract

Two, twelve week feeding trials were conducted to determine the performance of juvenile and yearling rainbow trout (Salmo gairdneri) which were fed high-fat or high-carbohydrate diets. In each feeding trial and for each diet group, 50% of the fish used had been previously treated with 17a-methly-testosterone, given orally at the onset of feeding. These were called treated fish. Also, for each group, 50% were untreated rainbow trout (controls), kept and fed under identical conditions as treated fish. All fish were held in 100% flow-through systems and fed twice or three times daily. Feed requirement was determined as a percentage of the total fish weight for each tank, according to water temperature and average size of fish calculated at each growth check. Three replicates were used in the first feeding trial and two in the second. Growth measurements were made every three weeks. Performance was determined through feed conversion efficiency, actual weight gain, actual length gain, relative weight gain and condition factor. Plasma glucose and ammonia levels, and visceral fat levels were measured to obtain an estimation of the effects of diet and treatment on these parameters.

Two diets were Formulated in t he first trial, one high in lipid (24. 1%) with no carbohydrate added and the other lower in lipid l15%) and high in sucrose (23.8%) as a digestible carbohydrate. In the second trial three diets were formulated: one high in fat (24.1% lipid), one high in sucrose (25.8%) and low in lipid (14.1%), and one high in molasses (42.0%) and low in lipid. All diets were iso-nitrogenous and iso-caloric. The objective in these studies was to determine if a correlation existed between performance of treated or control rainbow trout and diet fed. In the first feeding trial, fish fed the sucrose diet performed better than those fed the high-fat diet. Treated fish on the sucrose diet out-performed all other groups with respect to growth parameters, though not significantly so in all instances. A positive correlation was found between treatment with methyl-testosterone and low plasma glucose and low visceral fat levels in fish fed these diets. In the second feeding trial a molasses (an alternate carbohydrate source) diet, a sucrose diet and a high-fat diet were fed to treated and control fish. Fish in general performed better when fed the two diets high in carbohydrate. Molasses in the fish diet had no adverse affect on growth and results indicated that this sucrose source might potentially be used as a feed additive for fish. Treated fish fed the high carbohydrate diets in the second trial did not demonstrate the superior performance which was evidenced in the first trial. Results which were obtained from these feeding trials are discussed and possible implications for the aquaculture industry are put forth.

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