Factors limiting successful reproduction in wild silver carp, Hypophthalmichtys molitrix, in Kherrata Reservoir, Algeria

Silver carp, Hypophthalmichtys molitrix (Cyprinidae), is the most important freshwater fish in Algerian aquaculture. No natural spawning is observed in Algerian water bodies. This study was conducted with the aim of investigating silver carp reproduction in the wild in Algeria. This investigation can contribute tools to facilitate successful artificial reproduction. Macroscopic and histological analysis of the gonads was conducted, and the monthly distribution of maturity stages and oocyte diameters were monitored in an aggregate sample of 130 male and female silver carp, H. molitrix, (450-710 mm total length). The gonadosomatic index (GSI) ranged from 2.76 to 18.88% in females and from 0.34 to 1.85% in males. The female GSI values were the highest from June to August indicating the onset of the spawning season. The histological structures of the gonads revealed five different developmental stages in females and three stages in males. The oogenesis stages were the perinucleolar stage, the yolk vesicle stage, the primary yolk, the secondary yolk, and the tertiary yolk. Migratory nuclei and hydrated oocytes, which are considered to be the maturation stage, were not observed. Three different spermatogenesis phases (immature, maturing, and mature testis) were identified, which included final spermatozoa maturation.