Gonad Development and Fecundity of the Sand Goby, Gobius minutus Pallas

This paper describes gonad development and fecundity of the sand goby, Gobius minutus, in the Ythan estuary, Scotland. Sand gobies survived a maximum of about 22 months so that the longest lived fish experienced two breeding seasons. The gonads of underyearling fish matured in February, while those of yearling fish entering their second breeding season matured in December. Underyearling fish bred until June each year. The gonads of larger underyearling females increased in weight earlier than those of smaller underyearlings, but this did not appear to be true of the gonads of males. Fish size apparently did not influence the timing of the decline in gonad weight at the end of the breeding season. The maturing eggs in the ovaries of underyearling females could be recognized by December. In mature or ripe ovaries a second group of maturing eggs could be distinguished. The average fecundity of underyearling gobies was 2,556 in 1967 and 2,749 in 1968. Two of three yearling females had very low fecundities. Sand gobies showed the usual positive correlation between size and fecundity, however, there was also a strong correlation between month of capture and fecundity, fish captured later in the season having a higher fecundity. Because of the timing of maturation I concluded that simple photoperiod or temperature effects were not sufficient to explain the timing of gonad maturation. Also current hypotheses appear insufficient to explain seasonal and year to year variations in fecundity.