Long-term reproductive effects of chronic dietary petroleum exposure on polar cod (Boreogadus saida)

Abstract

Increased human activities in the Arctic pose a high risk for Arctic organisms to be chronically exposed to petroleum compounds. The endocrine disrupting properties of some of these compounds coupled with the metabolic costs of detoxification may have negative effects on the long and energy intensive reproductive development of polar cod, an Arctic keystone species. In the present study, selected reproductive parameters were examined in wild caught polar cod from Svalbard exposed to crude oil through a natural diet (0.11, 0.57 and 1.14 μg crude oil g-1 fish day-1) over a 31-week period prior to spawning. In the experimental period from June to February, fish experienced a light and temperature regime from Svalbard (79°N). Fish maturing in the current reproductive period made up 84% of experimental population while 7% were identified as resting fish, which would most likely not spawn this season. Portions of the male and female population were confirmed to be iteroparous. Males began investing in gonadal development in October, 2-3 months earlier in the season than females and 75% of maturing males could be stripped when the experiment concluded in February. Sex steroid hormone plasma levels (estradoil-17β (females), testosterone (males and females) and 11- ketotestosterone (males)) were low in immature and fish in early maturation and then steadily increased with increasing gonadal weight in maturing fish. The investigated endpoints of growth, investment and timing in gonadal development, and sex steroid hormone levels were not significantly altered by chronic dietary exposure to crude oil. However, reduced sperm motility was seen in measures of progressive sperm and sperm velocity in low and high crude oil exposures. A trend towards a delay in onset of vitellogenesis in crude oil exposed females was observed. Tradeoffs between pollutant detoxification and reproductive investment may have influenced maturation in exposed males. This study created novel data on polar cod reproductive physiology. However, the ecologically realistic doses used in this chronic exposure study were likely not high enough to induce widespread endocrine disruption effects.