Why are larger convict cichlid (Cichlasoma nigrofasciatum) fry sometimes adopted into broods of smaller fry?

Abstract

Convict cichlids (Cichlasoma nigrofasciatum)are substrate-brooding fish, native to Central America, with extended biparental care of young. Parents in the field and laboratory readily adopt foreign young of similar size to or smaller than their own, but usually reject larger foreign young. Under certain circumstances, the adoption of unrelated young has been shown to be adaptive to both donating and foster parents through (1) the dilution effect: the probability that their own young will be captured by a predator is reduced as the brood size increases; and (2) the differential predation effect: smaller young are more easily caught by brood predators than are larger young. These effects are not mutually exclusive. It has been demonstrated that parents of young with a standard length (SL) of 8 mm or bigger reject larger foreign young less often than do parents guarding smaller young, suggesting that the differential predation effect, and interfry aggression, may only be at work at smaller young sizes. In this study relative vulnerability of young to small gape predators (sub-adult conspecifics) decreased with increasing size of young (Fig. 1). When young were most vulnerable to predators (less than 8 mm SL) there was little or no benefit from dilution with larger young. However, as the young grew, the benefit of dilution with larger fry increased (Fig. 2).

Intraspecific brood adoption in the convict cichlid with respect to fry of two colour morphs

“… Fraser et al, 1993), parents should be reluctant to accept alien fry larger than their own into their brood. Nevertheless, this was recorded in a few of the experiments in the present study, and is also reported previously (Lorenzen, 1989;Fraser & Keenleyside, 1995). Since small alien fry represent food to adults as well as to their young, especially those near independence, it should be beneficial for parents with big young to adopt also the smallest alien fry.…”

The effects of kin and familiarity on interactions between fish

“…Members of the cichlid family, who often provide a high degree of parental care for their young, are known to have the ability to discriminate between related and unrelated offsprings ( Hemichromis bimaculatus , Kuhme 1963); Cichlasoma citrinellum , McKaye and Barlow 1976). Furthermore, convict cichlid ( Cichlasoma nigrofasciatum ) parents have been shown to actively recruit unrelated fry from other nests, possibly in order to dilute the predation risk to their own brood (Fraser and Keenleyside 1995).…”

Genetic evidence for mixed broods and extra-pair matings in a socially monogamous biparental cichlid fish

“…The Neotropical convict cichlid (Amatitlania siquia) is putatively one such species. Convict cichlids are substrate brooders that provide extended biparental care of young (6-8 weeks), from the egg stage through to the exogenous feeding/free-swimming ('fry') stage and until the fry reach independence at a standard body length of 10-12 mm Fraser & Keenleyside, 1995;Wisenden, 1995). As fry age and increase in length, the brood and parents become a mobile group, swimming and foraging along the river substratum during the day Wisenden, 1995).…”