By Morgan Bender
Chose fish carefully, anesthetize efficiently, tag tactfully, measure and weigh accurately, place promptly in tank, repeat 700 times!!
This was the latest progress on the long-term exposure experiment. Despite the 25 degree sunshine blessing Kårvika, the biological station on Ringvassøya, Jasmine and I have toiled inside in the cooled 6 degree seawater lab. Over the course of 2.5 days, we have placed small rice grain sized PIT tags intraperitoneally in 716 polar cod, which will be exposed to three different doses of crude oil mixed with a diet of Calanus over the course of 6 months starting in the beginning of July. Initial measurements of length and weight were taken using a fancy fish measuring board that communicates with an antenna reading the tag inside the fish. The polar cod were admittedly quiet hardy and accepted the tags without much of a flinch in their sleepy state. These fish will be followed for changes in sexual hormone levels, growth, reproductive development, and energy, enzyme activities, and PAH concentrations in select tissues. Most fish are in a post spawning or immature stage with many larger fish in a thin state. We selected fish for the experiment from the many hundred collected during Polar night cruise this January based on size and condition, only “average” sized fish with some “meat on their bones”. With 1000+ choices, we hope that our quick decisions during netting will bring us closer to an even sex ratio. Our final experimental design includes a few extra tanks than previously planned; an addition control tank was added to be followed more attentively with narrower intervals between sampling events, allowing us to time sampling of the treatment tanks utilizing baseline knowledge from our “population” in the lab. We have also included two tanks that will provide information on significance of timing and recovery in the response to dietary crude oil exposure. One tank will not be exposed until after vitellogenesis, a central stage in the development of eggs and the other tank will be switched from a high dose to clean food at this same point, thus giving us information about recovery of fish. Currently all tanks are under a midnight sun light climate with 3 degree seawater, these conditions will change with the season to ensure that fish receive the necessary environmental queues to signal reproductive development. With fish happily settled in their new homes for the next six months, I start my next task- making 150 kilos of Calanus J‑ello shots laced with crude oil! Mathilde and Morgan tagging the last 250 polar cod on the last day!!