Ecomorphological correlates of interspecific plasticity in reproductive investment and egg production of some cichlid fishes (Cichlidae) of a Nigerian rainforest stream

Abstract

Interspecific variability and trends in the reproductive investment and fecundity of four sympatric cichlid species (Thysochromis ansorgii (BOULENGER 1901), Chromidotilapia guntheri (SAUVAGE 1882), Hemichromis fasciatus PETERS 1852, Tilapia mariae BOULENGER 1899) were studied in Ikpa River vis-a-vis certain ecological and morphological attributes. There was a positive allometric functional relationship between mean total length and total weight; mean body condition increased with mean length; mean ovary weight and egg weight increased with mean fish length and weight (minimum in T. ansorgii and maximum in T. mariae in each case). Gonadosomatic index increased only slightly with mean fish length. The hierarchy of mean absolute fecundity was: C. guntheri>T. ansorgii>H. fasciatus>T. mariae. Mean absolute fecundity increased with mean length and weight among the substrate-spawners (T. ansorgii>H. fasciatus>T. mariae) while C. guntheri, a paternal mouth-brooder, was an outlier in these relationships. Interspecific divergence in reproductive investment, fecundity and morphometric attributes of the cichlids (CV = 10.1-149.5 %) may enhance reproductive niche partitioning, a phenomenon which provides the fundamental biomechanism for the evolution of their distinct reproductive strategies. This explains in part, the coexistence of these cichlids in the vegetated marginal water biotope.