The Osmoregulatory Role of the Thyroid Gland in the Starry Flounder, Platichthys Stellatus

Abstract

Energy demands for osmotic regulation and the possible osmoregulatory role of the thyroid gland were investigated in the euryhaline starry flounder, Platichthys stellatus. Using a melting-point technique, it was established that flounder could regulate body fluid concentration independently of widely divergent environmental salinities. Small flounder experienced more rapid disturbances of body fluid concentration than large flounder after abrupt salinity alterations.The standard metabolic rate of flounder adapted to fresh water was consistently and significantly less than that of marine flounder. In supernormal salinities standard metabolic rate was significantly greater than in normal sea water. These findings agree with the theory that energy demands for active electrolyte transport are greater in sea water than fresh water.Thyroid activity was studied in flounder adapted to fresh water and salt water. Percentage uptake of radioiodine by the thyroid was shown to be an insensitive and inaccurate criterion for evaluating thyroid activity in different salinities because removal rates of radioiodine from the body and blood differed between fresh water and marine flounder. Using thyroid clearance of radioiodine from the blood as a measure of activity, salt-water flounder were shown to have much greater thyroid clearance rates and, hence, more active thyroid glands than flounder adapted to fresh water. The greater activity of the thyroid of marine flounder correlates with greater oxygen demands in sea water and suggests a direct or adjunctive osmoregulatory role of the thyroid gland of fish.

Studies on the relationship between osmotic or ionic regulation and thyroid gland activity in two salmonid fishes, Salmo gairdneri Richardson and Oncorhynchus kisutch Walbaum

“…Similarly, these findings disagree with those of Hickman (1959) who found more rapid clearance of radioiodide in flounders in sea water compared with those in fresh water. However, the former authors attempted to compare freshwater and marine species, the same species was not acclimated to the two media, and the observations of Hickman (1959) may simply reflect the increased iodide availability in seawater-adapted fish compared with those acclimated to fresh water.…”

Standard metabolic rate of pike, Esox lucius: variation among studies and implications for energy flow modelling

“…The earliest work (Dolinin, 1973) employed a mask respirometer in which the fish was severely constrained. According to Hickman (1985) heightened metabolism may occur in some species if the fish volume exceeds 10% of the respirometer box volume and on this basis Dolinin's apparatus would seem likely to cause elevation in resting metabolism. However, Dolinin's estimates of metabolism at low temperatures were closely similar to those of Diana (1982) and Armstrong et al (1992) who used more expansive respirometer systems.…”

Changes in Behaviour during Starvation of Herring and Plaice Larvae

“…In terms of behaviour little is known. Certainly standard oxygen consumption falls in adult fish during starvation (Hickman, 1959;Beamish, 1964). Ivlev also described how feeding activity and stamina decrease, and susceptibility to predatio~ increases, during starvation in some freshwater fish.…”