Hypoxia Disruption of Gonadal Development in Atlantic Croaker

Hypoxia (DO<2 mg^.L^-1 O₂) naturally occurs in many water bodies, but anthropogenic influences have increased intensity and duration, likewise increasing its influence on fisheries. Hypoxia has been shown have an effect on reproduction, such as, reducing gonadal somatic index. Atresia is a natural process in ovaries after females undergo breeding, but stress promotes reabsorption of follicles and younger oocytes before breeding, at rates higher than normal.

 Atlantic croaker were collected in Chesapeake Bay, MD and exposed to hypoxia or normoxia 96 (n=5 and n=5) or 168 hr (n=2 and n=2) in controlled laboratory settings. Gonadal somatic index was measured and ovary stage determined by histology, among all treatments and times. The intensity of atresia in pre-ovulating ovaries will be measured to determine if hypoxia exposure increases atresia rates higher than non-exposed fish.

 All females showed similar GSI at 96 hr, but GSI of normoxic croaker was greater than hypoxic at 168 hr. Similarly, 168 hr normoxic croaker showed more later stage developed oocytes than 168 hr hypoxic fish. Atretic intensity has yet to be determined.  The reduced gonadal somatic index and developed oocytes will likely correspond with a greater intensity of atresia in females exposed to hypoxia.