Age, growth, gonadosomatic index and diet composition of Crimean barbel, Barbus tauricus (Actinopterygii: Cypriniformes: Cyprinidae), in a small Stream in NE Turkey

Abstract

Background. Crimean barbel, Barbus tauricus Kessler, 1877, is a riverine cyprinid fish commonly found in well-oxygenated streams with gravel bottom in the Black and Azov Sea basins. Its population has plummeted in the Salgir, Chornaya, and Alma rivers (Crimea) and hence this fish has been listed as Vulnerable on the IUCN Red List. The knowledge about its age, growth, length–weight relation, spawning period, and diet composition are either scarce or not available. This paper aimed to fill the existing gaps in the knowledge by describing selected biological characteristics of B. tauricus in the Çiftekavak Stream, in the outskirts of the city of Rize, NE Turkey. Materials and methods. Crimean barbel were collected by electrofishing (60 Hz pulsed DC) from April to November 2014. The total length (L, cm) and weight (W, g) of each specimen were recorded, and sagittal otoliths, gonads, and gut contents were then recovered. The length–weight relation (LWR) was calculated by a simple power function W = aLb. The age rings on sagittal otoliths were counted to determine fish age that was later used to analyse their growth by various growth models. The wet weight of gonads was used to calculate the gonadosomatic index (GSI). The gut contents were identified to the lowest possible taxonomic level and the contribution of a prey in the total diet composition was analysed by the occurrence frequency of prey groups (%O) and by numerical percentage frequency of prey groups (%N). Results. The age ranged from 0 to 4 years and more than 50% of the fish represented the 0-year group followed by 1-year group (21.9%) and 2-year group (13.5%). The von Bertalanffy growth model adequately described the correlation between the fish length and the age and indicated that females grew faster than males. The LWR identified negative allometric growth patterns in males and females. The higher values of GSI from males and females were recorded from April through July, while the lowest value of GSI was observed from September through November indicating the completion of the spawning season. A total of 14 prey items (including sand grains) were identified from the guts of Crimean barbel. The main prey items were Culex sp. (larva + pupa + adult), Chironomidae, followed by Ephemeridae and Zygoptera. They constituted up to >78%O (>95%N) of the diet. Conclusion. The results of this study will assess the conservative regulations and policies that will eventually provide a sustainable management of Crimean barbel stocks.