title: Influence of ration level and salinity on circulating thyroid hormones in juvenile Atlantic salmon (Salmo salar).
abstract: Following acute exposure to seawater (30 ppt), plasma thyroxine (T4) of Atlantic salmon (Salmo salar) smolts increased 80% in the first 6 hr, declined to initial levels after 24 hr, and remained stable for 18 days thereafter. In nonsmolts, plasma T4 did not rise immediately after exposure to seawater, fell slightly after 2 days, and remained low for 18 days. Plasma triiodothyronine (T3) of smolts and nonsmolts was not affected by acute exposure to seawater. To examine the effect of long-term adaptation to ration and salinity, Atlantic salmon smolts were acclimated to three salinities (0, 10, and 30 ppt) and four ration levels (0, 0.2, 0.8, and 1.6% wet weight per day) for 6 weeks. Plasma T4 increased with increasing ration level (P less than 0.001) but was not significantly affected by salinity (P = 0.4). Plasma T3 also increased with increasing ration (P less than 0.001) and was more strongly correlated with ration level (r = 0.85) and growth rate (r = 0.88) than was plasma T4 (r = 0.73 and 0.75, respectively). At low ration (0 and 0.2% per day), fish in 10 ppt had slightly but significantly lower plasma T3 than fish in 0 ppt. There was no effect of salinity on plasma T3 at the higher rations, nor did plasma T3 levels differ significantly in fish in 0 and 30 ppt at any ration. The results indicate that ration level is a more important influence on circulating levels of plasma thyroid hormones than is salinity.
authors.affiliation: Department of Fisheries and Oceans, St. Andrews Biological Station, New Brunswick, Canada.
authors.forename: S D
authors.initials: SD
authors.lastname: McCormick
authors.forename: R L
authors.initials: RL
authors.lastname: Saunders
mesh_terms: D000818:Animals; D005508:Food Deprivation / Q000502:physiology*; D006128:Growth; D011863:Radioimmunoassay; D012474:Salmon / Q000502:physiology*; D012623:Seawater; D012965:Sodium Chloride / Q000494:pharmacology*; D013974:Thyroxine / Q000097:blood*; D014284:Triiodothyronine / Q000097:blood*
chemical_list: D014284:Triiodothyronine; D012965:Sodium Chloride; D013974:Thyroxine