The costs of reproduction to males and females of a paternal mouthbroodingcardinalfish Apogon notatus

In the cardinalfish Apogon notatus, starving males mouthbrood the eggs, and females are more active than males in courtship and in attacks against con specific intruders upon their breeding territory, but sexual ornaments are developed in males. Condition factor, hepatosomatic index and fat body-soma tic index declined in both sexes during the breeding season. The deteriorat ion of somatic condition was more severe in females, suggesting that the ov erall energetic costs were larger for females which produced more than twic e as many clutches as males brooded in a season. Selective mortality of fem ales could be due primarily to the depletion of their energy reserves. The increased mortality in females is a possible mechanism for the male-biased operational sex ratio which may provide the potential for sexual selection on males. (C) 2001 The Fisheries Society of the British Isles.