Some Complicating Factors in the Study of the Calcium Metabolism of Teleosts

A number of factors which may complicate studies dealing withthe calcium metabolism of teleosts are pointed out. Thus, lowenvironmental levels of calcium markedly affect both gill RNAand sodium metabolism in dilute sea water, and the absence ofmonovalent cations affects calcium metabolism in dilute environments.Hypophysectomy is not always followed by the disappearance ofcortisol from the plasma, and prolactin—which is requiredfor the survival of either hypophysectomized or intact animalsin a divalent ion-free environment—stimulates cortisolproduction. It is also pointed out that Fundulus kansae can be maintainedin divalent ion-free environments for long periods, and thatcalcium is mobilized from internal reservoirs such as acellularbone and scales. Failure to survive in such environments isdue to the regulatory effect of environmental calcium on sodiummetabolism rather than on calcium metabolism per se. Finally,it is pointed out that while one parameter of calcium metabolism—suchas plasma calcium levels in male fish—may remain constantthroughtout the year, other parameters such as calcium uptakemay vary considerably. Seasonal differencees in responses tomammalian calcitonin have also been noted.