Influence of photoperiod on the onset of gonadogenesis in Eurasian perch Perca fluviatilis

The aim of the study was to improve our knowledge on the environmental control of Eurasian perch, Perca fluviatilis, reproductive cycle and determine the effects of photoperiod regimes on the onset of gonadogenesis. Under ambient thermal conditions, three photoperiodic regimes were tested in triplicate: a continuous photophase (24L/0D), a constant photoperiod (16L/8D) and a natural photoperiod. The gonadosomatic index (I-G) was calculated and plasma estradiol (E-2) and testosterone (T) levels were measured. This study showed that a 24-h photophase, applied to fish from mid-July to the beginning of October, inhibits the initiation of gametogenesis (I-G below 2% and 1% in females and males, respectively). A constant photoperiod (16L/8D) resulted in a very heterogeneous gonadal development. Twenty percent of females and 40% of males developed their gonads and mean I-G reached lower values than in females and males from the natural photoperiod. In the natural photoperiod treatment, gonadal development in all fish was comparable to that of fish observed in natural habitat at the same period of the year (I-G above 3%). Seasonal variations in daylength seem to be involved in the initiation of gametogenesis in perch, whereas continuous photophase inhibits gonadal development. Photoperiodic variations play a crucial role in the initiation of perch reproduction. (C) 2004 Elsevier B.V. All rights reserved.