Haemoglobin genotypes in cod (Gadus morhua L): their geographic distribution and physiological significance.

Haemoglobin polymorphism in cod (Gadus morhua L) has been investigated throughout the last 50years. Field studies have shed light on the geographic distribution of the two common alleles (HbI(1) and HbI(2)), and laboratory studies have shown effects of genotype on physiological traits such as growth, reproduction and hypoxia tolerance. The geographic distribution of alleles shows a correlation with temperature, with increasing frequency of HbI(1) in warmer areas. This is likely due to temperature-related differences in oxygen affinity of the three genotypes. We provide a general ecological introduction to cod haemoglobin polymorphism and a detailed discussion of physiological studies, particularly laboratory growth studies. Although differences in oxygen uptake are almost certainly a contributory mechanism to observed differences in traits such as growth rate, many other environmental, behavioural and social factors may also contribute, making it difficult to quantify the effect of HbI either experimentally or in the field.

Precision-cut liver slices to investigate responsiveness of deep-sea fish to contaminants at high pressure.

While deep-sea fish accumulate high levels of persistent organic pollutants (POPs), the toxicity associated with this contamination remains unknown. Indeed, the recurrent collection of moribund individuals precludes experimental studies to investigate POP effects in this fauna. We show that precision-cut liver slices (PCLS), an in vitro tool commonly used in human and rodent toxicology, can overcome such limitation. This technology was applied to individuals of the deep-sea grenadier Coryphaenoides rupestris directly upon retrieval from 530-m depth in Trondheimsfjord (Norway). PCLS remained viable and functional for 15 h when maintained in an appropriate culture media at 4 °C. This allowed experimental exposure of liver slices to the model POP 3-methylcholanthrene (3-MC; 25 µM) at levels of hydrostatic pressure mimicking shallow (0.1 megapascal or MPa) and deep-sea (5-15 MPa; representative of 500-1500 m depth) environments. As in shallow water fish, 3-MC induced the transcription of the detoxification enzyme cytochrome P4501A (CYP1A; a biomarker of exposure to POPs). This induction was diminished at elevated pressure, suggesting a limited responsiveness of C. rupestris toward POPs in its native environment. This very first in vitro toxicological investigation on a deep-sea fish opens the route for understanding pollutants effects in this highly exposed fauna.