Immunological cross-reaction between pituitary gonadotropin from North Atlantic fish

Pituitary extracts of 14 species of fish from the North Atlantic were tested in rainbow trout and carp gonadotropin radioimmunoassays (RIA). The poor cross-reaction and low gonadotropin content measured in the pituitary extracts indicate that RIA used for trout and carp gonadotropins are unsuitable for these species. The degree of specificity in the two systems does not reflect the phylogenetic relationships of the tested species. It is suggested that fish gonadotropins are species specific so that a sensitive RIA must be developed for each family investigated. A species specificity between fish and mammalian gonadotropins was suggested by work on goldfish spermatogenesis (Billard et al., 1970; Billard and Escaffre, 1973). Specificity among some groups of freshwater fish has also been indicated by other work on gonadotropins (Burzawa-Gérard and Fontaine, 1972; Fontaine et al., 1972; Breton et al., 1973). However during the final stages of gametogenesis (ovulation and spermiation) the species specificity appears to be less pronounced since human chorionic gonadotropin or heterologous pituitary preparations are potent treatments (cf. reviews by Pickford and Atz, 1957; Barnabé and René, 1972; Kuo et al., 1973; Shehadeh et al., 1973; De Vlaming, 1974). In the present study the immunological cross-reaction between pituitary preparations of a variety of fish species was tested in order to extend the investigation of species specificity and to examine the possibility of gonadotropin measurement in other species using carp and trout radioimmunoassay (RIA) systems already available (Breton et al., 1971; Breton and Billard, 1977)

Plasma growth hormone levels during sexual maturation in diploid and triploid rainbow trout (Oncorhynchus mykiss)

International audiencePlasma growth hormone concentrations were determined in diploid and triploid rainbow trout of both sexes during sexual maturation. Diploid females grow large ovaries, whereas triploid female trout show no ovarian development. The plasma growth hormone concentration in triploid female trout remained low and unchanged throughout the study, whereas it rose slightly, but significantly, in the diploid females that matured, but not in those that remained immature. On the other hand, triploid males do develop tests like their diploid counterparts. In both groups spermiation was accompanied by a steady rise in the plasma growth hormone concentration. The results suggest that the elevated growth hormone concentration in mature male trout was a consequence not of reproduction per se, but of the loss of condition that accompanied spawning. This hypothesis was supported by the results from the females. Apart from a temporary loss in the mature diploids caused by stripping of the eggs, female trout did not lose condition, neither did they show any change in the plasma growth hormone concentration during the period when they ovulated. These results suggest that it was the nutritional insufficiency accompanying reproduction in male fish that caused the elevation in growth hormone concentration. In fact, a strong negative correlation between the plasma growth hormone concentration and the condition factor of the fish was observed