Gonochorism and sex-inversion in British Labridae (Pisces)



An investigation was made to compare the reproductive strategies of Crenilabrus melops, Labrus bergylta, Labrus ossifagus, Centrolabrus exoletus and Ctenolabrus rupestris. Fish were collected monthly and measurements were made of length, weight, age and colouration. Histological sections of the gonads were also prepared. Labrus bergylta and L. ossifagus are protogynous, the former monandric and the latter diandric, and a distinct colour change is associated with sex-inversion in L. ossifagus. The other three species are gonochoristic and only C. melops exhibits sexual dimorphism which involves body colouration and size of the urino-genital papilla.

All five species undergo normal annual cycles of reproduction which compare with those described for other teleost species, but some differences were noted relating to the different reproductive strategies. L. bergylta females reached sexual maturity at the late age of six to nine years following earlier abortive maturation.

In C. melops two types of male were found: the normal (type 1) males and a minority group (about 20%) termed type 2 males, which have complete female secondary sexual characteristics. Type 2 males also have very large testes and attain sexual maturity two years earlier than type 1 males. Their role in reproduction is unknown.

Sexual inversion in L. bergylta and L. ossifagus occurs by atrophy of the oocytes and the gradual development of spermatogenetic cysts throughout the gonad. Primary and secondary testes can be distinguished histologically and male L. ossifagus with primary testes do not seem to take part in reproduction.