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

Abstract

Given its correlation to a number of other life history parameters including reproduction and survival, growth remains one of the most widely studied life history traits of fishes (Martin 1949, Beverton and Holt 1957, Beverton 1992, Hotos and Katselis 2011). Length–weight relation (LWR), Fulton’s condition factor (K), and the relative condition factor (Kn) are some of the most widely used morphometric indices to assess fish condition (Froese 2006). Differences in the parameters of LWRs and other condition indices represent spatial variations (Sparre and Venema 1998) and mirror the influence of abiotic factors and food availability on fish growth (Mommsen 1998). In natural populations, it seldom is possible to delineate the influences of extrinsic (environmental) and intrinsic or genetic (age, sex) factors on fish growth. Besides, younger and older life history stages are ill represented in the commercial fish catches, which provide the bulk of samples from natural populations. Alternatively, laboratory studies offer a suitable alternative by offering sufficient control over the environmental variables and also by providing access to all life history stages. Nonetheless, laboratory growth experiments are not always an easy option (Magnussen 2007). As an attempt to overcome the inherent problems associated with acquiring the age-related growth indices and with understanding the effects of age on such indices, an annual fish—the redtail notho, Nothobranchius guentheri (Pfeffer, 1893) was used as model for aging studies. Such species are known as annual fishes since their life cycle appears to be completed within a single year (Myers 1952). Thus, the redtail notho was chosen for the presently reported study for the following reasons: • Being a laboratory model (Gerhard 2007), it gives a possibility to exercise control over the environmental variables and thus discern the effect of genetic variables (age and sex) on the growth indices; • Having a median lifespan of 12 months (Markofsky and Perlmutter 1972) it gives a possibility to obtain information on the growth indices for all the life history stages in a relatively short period; and ACTA ICHTHYOLOGICA ET PISCATORIA (2012) 42 (4): 291–296 DOI: 10.3750/AIP2012.42.4.02