Disc-electrophoretic identification of prolactin in the cichlid teleosts Tilapia and Cichlasoma and densitometric measurement of its concentration in Tilapia pituitaries during salinity transfer experiments

The prolactin band was identified after disc electrophoresis of pituitaries from Tilapia mossambica and Cichlasoma labiatum. Electrophoresis coupled with a densitometric procedure was validated as a means of measuring the prolactin content of Tilapia pituitaries during salinity transfer experiments. Transfer of T. mossambica from seawater or 33% sea water to fresh water was followed by a sharp decline in both plasma sodium and pituitary prolactin levels. One week after transfer, there was a recovery of sodium levels to normal, although pituitary prolactin concentrations had not yet reached the level found in fully acclimated freshwater fish. Pituitary prolactin levels in T. grahami were reduced by more than 50% on the day after transfer from Lake Magadi (alkaline–saline) water to fresh water. No such depletion of pituitary prolactin followed a transfer from 100% seawater or from fresh water to 33% seawater, indicating that this response is specifically linked to the secretion of prolactin for osmoregulation in fresh water. The molecular weight of Tilapia prolactin was estimated at 17 000 by means of electrophoresis in sodium dodecyl sulfate.

Mercury concentrations in museum specimens of tuna and swordfish

The mercury levels of museum specimens of seven tuna caught 62 to 93 years ago and a swordfish caught 25 years ago have been determined by instrumental neutron activation analysis. These levels are in the same range as those found in specimens caught recently.