Reproductive Condition in the Caspian Anadromous Shad Alosa kessleri kessleri (Alosidae) during Spawning Migration in the Volga River

Abstract

This paper describes the state of the gonads of Caspian anadromous shad, Alosa kessleri kessleri (Grimm, 1887), migrating for spawning in the Akhtuba River. In May of 2021, the peak of spawning was recorded at a water temperature of 17–18°C. Females and males had gonads at the developing and spawning-capable phases. The fork length (FL) of females averaged 254.1 mm, and their body weight was 178.9 g; for males, this was 209.9 mm and 87.5 g, respectively. Most females were over three years old, while males were between one and three years old. The gonadosomatic index (GSI) in females and males averaged 8.71 and 3.67%, respectively. Among the asynchronously developing secondary growth oocytes in the spawning capable gonads, three different-sized groups were distinguished for intending to spawn the same number of oocyte batches. The number of primary growth oocytes (26.7–59.4% of germ cells on sections) allows for considering these fish as iteroparous. The diameter of the tertiary vitellogenic oocyte was about 800 µm.