ARS | Publication request: AMMONIA EXCRETION AS AN INDICATOR OF GROWTH EFFICIENCY

Submitted to: Aquaculture America Conference
Publication Type: Abstract
Publication Acceptance Date: November 30, 2005
Publication Date: February 10, 2006
Citation: Silverstein, J., Brazil, B.L., Salem, M.S., Cox, M.K., Blemings, K.P., Yao, J. 2006. Ammonia excretion as an indicator of growth efficiency. Aquaculture America Conference. Aquaculture America Book of Abstracts. Pg. 285.

Technical Abstract: Improved growth and feed efficiency are key traits for genetic improvement. Recent studies at our center with individually housed rainbow trout have shown genetic variation for feed efficiency. From studies done on other animals and in fish it has been suggested that fast, efficiently growing animals have reduced protein degradation rather than increased protein synthesis relative to slow, inefficiently growing animals. For fish, ammonia generated through protein degradation can be quickly excreted through the gills, unlike other animals that cannot excrete ammonia quickly enough and must convert ammonia to a less toxic form before secretion. We reasoned that more efficient rainbow trout would degrade less protein, and therefore excrete less ammonia relative to their less efficient couterparts and designed a series of experiments to test this hypothesis. We compared ammonia excretion in a 3 week study between fed, unfed and unfed (2 weeks)/refed (1 week) groups. Water was sampled from fish tanks 20h after a meal and ammonia measured using ion chromatography. Significant differences in ammonia excretion were detected. The proteolytic pathways of calpains, cathepsins, proteosome and apoptosis were examined in tissues of these fishes at the end of the experiment. Calpastatin mRNA abundance was reduced and calpain activity increased in liver of unfed fish. Cathepsins did not respond consistently. Refeeding stimulated mRNA abundance and enzyme activity in the proteosome pathway. The mRNA abundance of apoptotic proteases caspace -3 and -9 increased in refed animals, too. The increase in proteosome and caspace activity may account for the increase in ammonia production of refed versus unfed fish. The higher rate of ammonia production in fed fish may be due to greater levels of substrate rather than greater enzyme abundance or activity.