HYPOXIC THRESHOLD FOR YELLOW PERCH (Perca flavescens) EMBRYONIC DEVELOPMENT

Hypoxic events, or low dissolved oxygen (DO) conditions, have been shown to affect the wide array of physiological processes in fish, including the embryonic development and hatching. However, the effects of hypoxia on the embryonic development of Yellow Perch have been sparsely documented in literature. In the first experiment, eggs from mature female (263.3g) were fertilized and immediately transferred to 12 aquaria under three different concentrations of dissolved oxygen - hypoxia, 3-4 mg/l (H); moderate-hypoxia, 5 mg/l (MH) and normoxia, 7-8 mg/l (N) in replicates of four at 16.8±0.4°C. Two egg baskets were placed in each aquarium containing average 1.58±0.1g fertilized eggs (631 eggs/g) and observed until the embryos hatched or began to show signs of slowed or ceased development. Embryos were collected periodically and development stages were observed under microscope. Significant differences (P< 0.05) were observed in terms of percent hatching and subsequent survival rates among the three treatments. In H treatment, all embryos were arrested or dead 43 hours after fertilization (haf) (Optic-cup stage); lens were visible in MH and N groups. In MH and N, approximately 20±8.7% and 78.3±8.6% were hatched after the same time and of them about 12±9.8% and 99±0.4% were alive, respectively. Heartbeat appeared at about 72 haf in N and about 96 haf in MH embryos and heart rate differed significantly (P<0.05) (N, 143±10/min; MH, 117±17/min). In the second experiment, 300 newly hatched larvae (approximately 72 haf) of perch were placed in each aquarium to observe the effect of different oxygen concentration on their survival. The highest mortality was recorded in H group (7±4.7%) followed by MH (6±0.2%) and N (3±0.4%), respectively. Overall, the results indicate that hypoxic conditions below 3.5 mg/l (35% saturation at 16°C) have a profound negative impact on the embryonic development and survival of Yellow Perch larvae.