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ABSTRACT
The seasonal histological changes in the ovaries of specimens of five species of Mugil caught in natural habitat were compared with those of specimens in fish ponds and Lake Tiberias.
Specimens of Mugil cephalus and Mugil capito confined to fresh water do not ovulate. The Gonado-Somatic Index (GSI) of the various species of mullets was compared. Throughout the year, the GSI is about 1. A steep rise of the GSI begins in the months proceeding the spawning season in the specimens caught in their natural habitat. In Mugil cephalus specimens from freshwater ponds the GSI does not exceed 1. In specimens of Mugil capito from freshwater ponds and from Lake Tiberias, as well as in specimens of Mugil cephalus from Lake Tiberias, the GSI is very high during the spawning season. In these specimens, unable to ovulate, the high GSI is due to accumulation of atretic oocytes. Histograms showing percentages of stages of oocytes of the various species of mullets are compared and the factors responsible for the infertility of the specimens confined to fresh water are discussed.