Sexual activity and ageing in the teleost fish, Rhodeus sericeus amarus

Abstract

The reproduction and ageing of the teleost fish, Rhodeus sericeus amarus, was studied in a colony of fish kept under natural conditions. Spawning occurs only in the presence of molluscs ( Unio pictorum), whilst the absence of Unios prevents reproduction. Morphological findings show that neither the testes, nor the ovaries revealed significant differences correlated with the presence or absence of Unios. There were no apparent changes of the gonads of either sex in the course of the fishes' life-span, which is estimated as approx. 3 1 2 yr. Similar results were found by the electron-microscopic evaluation of the cerebellum of the animals of various ages and kept with or without molluscs. The was no clear-cut relationship of lipofuscin-like substances to age. The breeding data obtained show that the nuptial colouring of the males as well as the process of ovulation of the females kept throughout their life-span without cockles occurred in the same way as in specimens kept with Unions. The process of laying eggs in the mantle cavity of Unio is not triggered by the neurosecretion of molluscs, as was formerly believed, but it is reflex-activity.