Sexual development, maturity and reproduction of dolphinfish (Coryphaena hippurus) in the western and central Mediterranean

Abstract

Studies have been conducted on the sexual development, maturity and reproduction of the dolphinfish (Coryphaena hippurus L. 1758) in the Mediterranean area, with special reference to the Balearic islands and Sicily. Professional fishing, carried out from August to December 1996, uses FADs (Fish Attracting Devices) and surrounding nets. 2087 juvenile specimens of dolphinfish from the Ionian and southern Tyrrhenian seas, the Strait of Sicily and the Balearic islands were sampled. A small number of adult fish (39), which are not usually caught in surrounding nets, was sampled in the swordfish long-line by-catch. The gonads of the young fish were analysed monthly to establish the stage of development of the ovaries or testes, during the first few months of life. The gonads of the adult fish, sampled in the months of June-September only, were all mature. The specimens caught between October and December presented maturity stage V in the case of the females and I in the case of the males, indicating the end of the reproductive period. The gonado-somatic index (GSI) and condition factor (CF) were calculated for both genders. The trend of the GSI confirms the presence of immature specimens as regards the juvenile fish; the low value of GSI was obtained for the adults, probably associated with the post-reproduction conditions found in the October-December period. Most of the gonads sampled during the months between August and December belonged to young specimens born in early summer. This is confirmed by the juvenile stages (FL 2.5 to 4.3 cm) caught with plankton nets in the Strait of Messina area in July.