Swimbladder filling in herring larvae: effects of food oil on the water surface

There has been a recent interest in exploring the possibility of oil and gas production in the Lofoten-Vesterålen area along the Norwegian coast. Since this is an important drift area for offspring of several important commercial fish species, such an activity could potentially have adverse effects on fish early life survival. A potential surface oil spill could coincide in time with swimbladder filling in herring larvae originating from major spawning grounds in Møre, upstream of Lofoten-Vesterålen. A laboratory experiment was carried out to determine possible effects on growth and survival of herring larvae by adding an oil slick to the water surface. The presence of food oil on the water surface over a two-week period significantly affected swimbladder filling in two-month-old herring larvae (18% vs 85% filled in exposed vs control group larvae). However, overall larval size-at-age and survival were not affected by the prevention of swimbladder filling per se, neither did otolith microstructure analysis indicate any short-term reductions in growth. Overall survival during the three-month experiment was high and averaged 74%. The relative condition of food oil-exposed larvae was higher than among control group larvae. Analysis of the larval samples and food oil documented the incorporation of specific fatty acids (e.g. 18:1 n-9, 18:2 n-6) from the food oil into the larvae. Since an oil slick represents a physical barrier and a source of bioaccumulation, further experiments should be undertaken to evaluate the toxic effects of incorporated mineral oil compounds during swimbladder filling in herring larvae.