The effects of elevated summer temperature and sublethal pollutants (ammonia, low pH) on protein turnover in the gill and liver of rainbow trout (Oncorhynchus mykiss) on a limited food ration

Protein synthesis, degradation and growth of the liver and gills were deter mined in juvenile rainbow trout (Oncorhynchus mykiss) fed a limited ration and exposed for 90 days to normal or elevated summer temperatures (+2 degre es C above ambient) and either low pH (5.2) in softwater or 70 mu M total a mmonia in hardwater. The limited ration resulted in low rates of growth (<0 .80% per day) and protein synthesis in all fish. In softwater, whole-body g rowth was significantly inhibited by elevated temperature but stimulated by low pH, although tissue protein metabolism was generally unaffected by the se treatments. There was no significant difference in final size between th e groups of fish in hardwater, but liver protein synthesis and degradation were significantly lower at +2 degrees C, the reduction in synthesis being due to an inhibition of both the capacity for protein synthesis, C-s and th e RNA translational efficiency, k(RNA). Gill protein metabolism was unaffec ted by the experimental treatments in trout in hardwater. The authors concl ude that a global warming scenario would be detrimental to protein synthesi s and growth in freshwater fish under conditions of food limitation in summ er, and when late summer temperatures approached the upper thermal limit of the species, regardless of food availability. (C) 1999 Elsevier Science In c. All rights reserved.