On brain, behaviour and biochemistry of the deep-sea demersal grenadier fish, Coryphaenoides (Nematonurus) armatus
In surface-dwelling vertebrates, pineal melatonin is secreted in a manner directly related to photoperiod. Despite an absence of solar light, several deep-water fishes show some seasonality. The presence of central melatonin receptors was investigated using in vitro autoradiography in the deep-sea fish Coryphaenoides (Nematonurus ) armatus. No specific 2-[125I]iodomelatonin (IMEL) binding was found in optic tectum, cerebellum or hypothalamus. Specific binding was however found over mid-brain tegmentum and hindbrain. Two possible cues in the deep-sea are seasonal depositions of phytodetritus and diurnal/semidiurnal currents. Both gustatory and acousticolateralis systems are well developed and capable of detecting such cues. The principle sites of specific IMEL binding are regions which integrate inputs from these non-optic senses. The behaviour of deep-sea scavenging fishes was investigated using a baited free-fall photographic and fish tracking system - AUDOS (Aberdeen University Deep Ocean System). Data collected during spring (April, 1994) at 4800m depth, NE Atlantic were compared with previous studies at the same location during summer, 1989. The time and species of first arrivals and mean staying time showed no differences between years or season. However, radial swimming speed (0.009 m.s-1) of C.(N) armatus was significantly slower than in previous studies. A change in size distribution to smaller individuals in spring 1994, might also suggest C.(N) armatus may undertake major episodic or seasonal migrations. The white muscle protein content of deep-water fishes is about 40% lower than in shallow-water species. This appears to be accompanied by lower numbers of ribosomes. Any increase in RNA content to compensate for low efficiency at low temperatures is not apparent and may be due to reductions caused by other factors.