Fundulus heteroclitus Gonadotropin(s) 2. Year-round husbandry of animals with active pituitaries and responsive follicles

Abstract

Mummichogs (Fundulus heteroclitus) were exposed to various regimens of temperature and photoperiod in order to develop a routine husbandry procedure so as to have throughout the year a population of reproductively healthy fish with a good quantity and quality of prematuration follicles (1.2-1.5 mm) suitable for carrying out homologous bioassays ofF. heteroclitus gonadotropin. During the fall and winter months, wild fish in the field all had regressed ovaries (gonadosomatic index <1). On the other hand, laboratory-maintained fish, with or without cold temperature (15°C) and short photoperiod (10 h light/day) pretreatment, generally had sexually mature ovaries (GSI>10) when maintained on a warm temperature (25°C) and long photoperiod (14 h light) protocol. Ovarian follicles retrieved from laboratory fish were responsive toF. heteroclitus pituitary extract stimulation, and underwent germinal vesicle breakdown normallyin vitro. Hence these ovarian follicles served well as a bioassay forF. heteroclitus gonadotropin even outside of the normal breeding season. The pituitary glands retrieved from laboratory fish in winter also retained high gonadotropic potencies, in terms of maturational and steroidogenic activities. Our results thus demonstrated that active gametogenesis in laboratory-maintained fish can be extended five months beyond the end of the normal breeding season. Apparently,F. heteroclitus in Florida is potentially a continuous breeder when under favorable conditions, but has a reproductive quiescent period imposed upon it by some environmental stressor(s). Although the design of the present experiments did not determine the relative importance of nutritional factors, temperature, and photoperiod on the annual reproductive cycle ofF. heteroclitus, there are indications that diatary factors may play a much more dominant role in the reproductive cycle than previously recognized.

Role of inhibin and activin in the modulation of gonadotropin- and steroid-induced oocyte maturation in the teleost Fundulus heteroclitus

“…It has been well documented that addition of FPE (used as a source of homologous gonadotropin hormones) to F. heteroclitus intact follicles cultured in vitro promotes an increase in the synthesis of 17α,20β-dihydroprogesterone (DHP) by the granulosa cells [33,38]. This steroid, DHP, has been demonstrated to be the natural maturation inducing substance in this species [35], and it acts directly on the oocyte to induce GVBD.…”

Neuropeptide Y in the forebrain and retina of the killifish, Fundulus heteroclitus

“…The fish were maintained in running sea water under conditions that maintained reproductive activity (Lin et al 1989) and were fed dry flake food and chopped shrimp ad libitum. Each fish was anesthetized with an overdose of ethyl m-aminobenzoate (tricaine; MS 222) and perfused transcardially with 10 ml ice-cold phosphate-buffered saline (pH 7.4) followed by 10 ml ice-cold Zamboni's fixative (Stefanini et al 1967).…”

Fundulus heteroclitus gonadotropins.5: Small scale chromatographic fractionation of pituitary extracts into components with different steroidogenic activities using homologous bioassays

“…Another advantage of our homologous bioassay system was that many fractions could be assayed simultaneously with a large number of appropriate-sized follicles that can be pooled from several fish and randomized, thus eliminating most of the between-animal variation in the procedure. To further minimize the inherent variation in the responsiveness of ovarian follicles to gonadotropin and to assure the availability of large numbers of sensitive follicles and active pituitary glands throughout the year, we also developed a routine husbandry procedure to maintain a large population of reproductively healthy F. heteroclitus in the laboratory [29]. With this husbandry procedure, we were able to proceed with the FPE fractionation and to carry out homologous bioassays throughout the year.…”

“…Routine husbandry procedures were used to maintain the fish in the laboratory: captured fish (average weight = 7 g) were kept in a temperature-regulated (25°C) running sea water aquarium with a controlled photoperiod (14L:10D) and were fed with an enriched diet (mixture of boiled chicken eggs and dry flake food). Under this regimen, the laboratory-maintained fish had responsive ovarian follicles and active pituitaries throughout the year [29]. In effect, the ovarian follicles retrieved from these fish were responsive to pituitary extract stimulation, and underwent oocyte maturation normally in vitro.…”