Seasonal variations in egg and larval quality in two multiple-spawner cyprinid fish, the bleak Alburnus alburnus and the white bream Blicca bjoerkna

Abstract

Variations in egg and larval quality along the reproductive season have been investigated in two multiple-spawner cyprinid fish (the bleak Alburnus alburnus and the white bream Blicca bjoerkna) by successive samplings of breeders in the River Meuse. Morphological and biochemical criteria were used to determine the quality of the ova. Larval quality was assessed morphologically and by stress test. The diameter of ova did not decrease significantly during the spawning season in both species, averaging 1.03 ± 0.03 and 1.06 ± 0.06 mm in bleak and white bream, respectively. Protein level of ova remained constant throughout the spawning season. A slight, non-significant increase of the total fatty acid content and docosahexanoic/eicosapentanoic ratio (DHA/EPA) was measured in bleak eggs as the spawning season progressed (mean ± SD = 20 ± 2.6% of dry matter content and DHA/ EPA = 3.7 in early spawning vs 26.2 ± 7.2% and DHA/EPA = 4 in next spawning). Regardless of the spawning period, the body weight and total length of bleak larvae issued from the first egg batches were constant, averaging 6.4 mm and 0.93 mg, respectively. However, bleak larvae issued from next egg batches were significantly longer, reaching 6.9 mm. In white bream larvae from first egg batches averaged 6.3 mm and 0.74 mg, but no larvae issued from fish spawning for a second time have been obtained. The resistance of larvae to extended fasting conditions was constant regardless of the period of spawning. Lethal time (TL50) ranged from 11 to 14 days, without significant differences between the rank of spawning within the reproductive season. On the other hand, the resistance of bleak larvae to osmotic shock (2 % NaCI) decreased significantly during the spawning period, from 40.9 ± 5.5 min in late June to 17.8 ± 0.7 min in late July.