Morphometric indices in an annual fish—the redtail notho,  Nothobranchius guentheri (Actinopterygii: Cyprinodontiformes: Nothobranchiidae): Influence of age and gender

Abstract

Background. Though fishes grow indeterminately, very little is known of the effects of age on the morphometric indices (length, weight, and condition) in fishes as it is often difficult to cover the entire lifespan of a species in laboratory or nature. The presently reported study was thus conducted to elucidate the effects of age (and sex) on the growth indices using the annual fish and a laboratory model of aging. Materials and methods. Experimental fish—the redtail notho,  Nothobranchius guentheri (Pfeffer, 1893), were obtained by hatching the diapause eggs of the same parental lineage and reared over their entire lifespan. Length–weight measurements were recorded from 3–12 months and various indices (length–weight relation, Fulton’s condition factor, and relative condition factor) were computed and compared statistically. Results. Mean lengths, weights, length–weight relations (LWRs), Fulton’s condition factor (K) and relative condition factor (Kn) varied significantly leading to differential indices based on age and sex. Age influenced all indices positively, which is indicative of the indeterminate growth typical of fishes. Conclusion. Age was not seen to suppress the growth indices in the annual fish, which is suggestive of a healthy and delayed senescence in the annual fish N. guentheri. Whether other short- and long-lived finfish follow the same pattern needs further investigation.

Keywords

• Annual fish; aging
• growth
• morphometric indices