Towards a universal scale to assess sexual maturation and related life history traits in oviparous teleost fishes

The literature presents a confusing number of macroscopic maturation scales for fish gonads, varying from over-simplified scales comprising three to four stages to highly specific and relatively complicated nine-stage scales. The estimation of some important life history traits are dependent on a correct assessment and use of the gonadal maturation scales, and frequent mistakes have been made in many studies. The goal of this report is to provide a synthetic, relatively simple, yet precise maturation scale that works for most oviparous teleost fishes. The synthetic scale proposed here is based on the correspondence between key physiological and cytological processes of gamete development and corresponding modifications observed at the macroscopic level. It is based on previous and ongoing studies of several fish species pertaining to some of the most important African and Neotropical taxa, including Characiformes, Siluriformes, Osteoglossiformes and Perciformes. This scale should allow for standardized protocols of field studies and improve intra- and inter-specific comparisons of life history traits. Guidelines on the correct use of this scale to estimate these life history traits are provided.