Effects of photoperiod-temperature regimes on pituitary gonadotrophs, pituitary gonadotropin potency and hypothalamic gonadotropin releasing acitivity in the teleost notemigonus crysoleucas

Abstract

1. 1.|The effects of various photoperiod-temperature regimes on gonadal activity, hypothalamic gonadotropin releasing activity, pituitary gonadotropin potency and pituitary gonadotrophs were examined in the teleost, Notemigonus crysoleucas. 2. 2.|In fish maintained on a long photoperiod-high temperature regime final gonadal maturation occurs. Under these conditions hypothalamic gonadotropin releasing activity is high, stainable gonadotrophs make up a low percentage of pituitary area and pituitary gonadotropin potency is relatively low. 3. 3.|Gonadotrophs make up a relatively large area of the pituitary and adenohypophyseal gonadotropin activity is high in fish exposed to long photoperiod-low temperature regimes. Long photoperiod-low temperature regimes do not stimulate final gonadal maturation. 4. 4.|Short photoperiod-high temperature conditions retard gonadal development or cause gonadal regression in Notemigonus. The area of the pituitary occupied by gonadotrophs and hypothalamic gonadotropin releasing activity are low in fish exposed to these conditions. Pituitary gonadotropin potency, however, is relatively high in fish maintained on short photoperiod-high temperature regimes. 5. 5.|Gonadotrophs were infrequent in the pituitary and pituitary gonadotropin potency was low in animals maintained on short photoperiod-low temperature regimes. These conditions do not promote the final stages of gonadal maturation in Notemigonus. 6. 6.|Light intensities of below 151x are insufficient to induce spawning in Notemigonus. Light intensities above 151x increase the incidence of spawning.