Features of Biology of Tonlesapia tsukawakii (Actinopterygii, Callionymidae) in the Mekong Delta, Vietnam

Abstract—

Tonlesapia tsukawakii Motomura et Mukai, 2006 is an endemic freshwater representative of the family Callionymidae (Teleostei: Perciformes: Callionymidei) living in the Mekong River. According to the materials of studies conducted in 2018–2022, the occurrence of the species in catches in the Mekong Delta averaged 20.7%, the proportion in terms of abundance was 2.6%, in terms of weight, 0.6%. The maximum values of the species parameters were 81.2 ind./effort and 176.2 g/effort, respectively. The abundance of fish significantly decreased in the conditions of low content of dissolved oxygen and on a substrate with plant residues. The sex ratio of T. tsukawakii was 1.0 : 3.1 with a stable prevalence of females, which distinguishes the species from other representatives of the family. Females have larger sizes compared to males and they gain weight faster. The fecundity of the species was determined for the first time; the average number of mature oocytes was 2950 psc. During a low-water period, callanoid copepods of the family Pseudodiaptomidae mainly represented by Pseudodiaptomus dauglishi Sewell, 1932 were the main food items of T. tsukawakii.