Osmoregulation in the mudskipper,Boleophthalmus boddaerti II. transepithelial potential and hormonal control.

Boleophthalmus boddaerti submerged in 10%, 50% and 80% seawater (sw) for 7 days, had whole body transepithelial potentials (TEP) of 3.3, 18.3 and 22.9 mV, respectively. Hypophysectomy significantly decreased the TEP ofB. boddaerti and reversed the polarity of the TEP of the fish exposed to 10% sw.Hypophysectomy also significantly decreased the branchial Na(+)-K(+) activated adenosine triphosphatase (Na(+),K(+)-ATPase) activity but increased the activity of branchial HCO3 (-)-Cl(-) stimulated adenosine triphosphatase (HCO3 (-),Cl(-)-ATPase) inB. boddaerti exposed to 10% sw. However, survival in 10% sw was not significantly impaired by hypophysectomy and no significant change in plasma osmolality and plasma Na(+) and Cl(-) concentrations was observed.Various doses of ovine-prolactin or salmon-prolactin were unable to restore the TEP of hypophysectomizedB. boddaerti in 10% sw to that of the sham-operated fish. However, cortisol increased TEP to a positive value in hypophysectomizedB. boddaerti, though it was still lower than the sham-operated control. Cortisol treatment also affected the plasma osmolality, plasma Na(+) and Cl(-) contents and branchial Na(+),K(+)-ATPase and HCO3 (-),Cl(-)-ATPase activities. Overall, the hormonal control of osmoregulation inB. boddaerti appeared to differ from that of other teleosts.

Effects of melatonin, serotonin, and naloxone on aggression in isolated cichlid fish (Aequidens pulcher).

Intracranial injections of 10 micrograms melatonin, with or without 4 micrograms naloxone, result in reduced aggressive responsiveness by the cichlid fish Aequidens pulcher to a mirror presented 20 min later. Naloxone, when administered on its own, had no behavioral effect. Intracranial injections of 25 micrograms serotonin-creatinine sulphate complex (5HT-CS) also reduced aggression. 5HT-CS's action was abolished if the injection included 10 micrograms S-adenosyl homocysteine (SAH), which inhibits the conversion of serotonin to melatonin. This suggests that the behavioral action of 5HT-CS may be mediated by its conversion to melatonin. There is inconclusive evidence to suggest that 37.5 micrograms 5HT-CS, administered in conjunction with 10 micrograms SAH, may reduce aggressiveness; injection of 50 micrograms 5HT-CS, with or without 10 micrograms SAH, induced a pronounced escape behavior which precluded any measurement of aggressiveness in the fish.

Steroid hormones and agonistic behavior in a cichlid teleost, Aequidens pulcher.

The effects of three steroid hormones on the agonistic behavior of female Aequidens pulcher have been evaluated. Testosterone, estradiol, and cortisol were tested using an immersion technique to minimize trauma, and we also examined metyrapone, a blocker of cortisol biosynthesis. Two different experimental protocols were employed, the first investigating agonistic interactions within groups of fish, and the second examining the responses of isolated fish to models and mirrors. Differences between replicates were small, and both protocols supported similar conclusions. Each of the three hormones produced a characteristically different spectrum of behaviors when compared to the controls. Testosterone increased agonistic behavior in all experimental situations, while estradiol had a generally opposite effect; this may reflect the natural modulation of behavior by hormones during the reproductive cycle of A. pulcher. Cortisol also had distinct behavioral effects; available evidence suggests that this steroid increases submissive components of agonistic behavior, and that observed increases in some aggressive components are an indirect consequence, dependent upon the feedback of social information received by each fish. Metyrapone treatment greatly reduced all agonistic behaviors, groups of fish forming shoals typical of juveniles. This was not reversed by replacement therapy with cortisol, which suggests that metyrapone affects behavior by an alternative, possibly toxic, mechanism.

The structure of the adenohypophysis of Aequidens pulcher (Teleostei, Cichlidae). I. Histological and immunohistochemical studies.

With standard staining techniques, five cell types can be identified in the pars distalis of the adenohypophysis of Aequidens pulcher; a sixth cell type prevails in the pars intermedia. Each of these cell types has been characterized immunohistochemically. Various treatments--metyrapone, thiourea, and thyroxine--have been used to confirm the identity of the corticotrophs and the thyrotrophs. It is concluded that the cells producing prolactin and growth hormone are tinctorially, immunologically, and topographically similar to descriptions for other teleosts. This also applies for the corticotrophs of the rostral pars distalis and the melanotrophs in the pars intermedia. The corticotrophs are stimulated by metyrapone treatment, on the basis of cell size and tinctorial properties, but immunohistochemical staining is not affected; thiourea, on the other hand, affects immunohistochemical, but not tinctorial, staining of the corticotrophs. The thyrotrophs are small, irregularly shaped cells in the rostrodorsal proximal pars distalis, adjacent to the neurohypophysis. They cross-react with an antiserum against bovine beta-TSH but (unlike the gonadotrophs) not with one against ovine LH. Thiourea treatment induces their hypertrophy, with a decrease in tinctorial and immunohistochemical stainability. Metyrapone, like thiourea, induces enlarged nuclei with pronounced nucleoli but, like thyroxine, also increases tinctorial and immunohistochemical staining. The gonadotrophs are basophilic, like the thyrotrophs, but cross-react with antisera against both bovine beta-TSH and ovine LH. These cells are not affected by any of the treatments used here. In some specimens, a second type of gonadotroph has been identified, which stains mainly with periodic acid-Schiff. The two types of gonadotrophs are immunohistochemically comparable.