FOOD AND FEEDING-HABITS OF FISH SPECIES OVER A SOFT SUBLITTORAL BOTTOM IN THE NORTHEAST ATLANTIC .1. COD (GADUS-MORHUA L) (GADIDAE)

Fishes were caught with bottom trawl at 55-75 m depth three times of the day on six occasions in one year. The food and feeding habits of all fish species caught were studied by stomach contents analysis, morphological examination, and a few aquarium observations. For interspecific comparisons, fishes of the same length were used whenever possible. Some basic, logical interpretations of the variables obtained by stomach contents analysis, and their incidental sources of error, are given. The cod's food spectrum included all types of prey of a wide size interval, and ranged from 'low-pelagic' to endobenthic (including many tubicolous) species. With increasing fish size, the feeding habitat widened vertically; concurrently, the mean feeding level lowered, and the food dominance changed from medium-sized, hyperbenthic prey to large, epibenthic and endobenthic prey. The cod's most outstanding feeding niche characteristic was its high feeding versatility: its long-term food diversity was clearly highest among the fish species in the area, and was highest in fishes c. 30 cm long. The cod is very discriminatory regarding the nutritional content of its food. The cod temporarily specialized its feeding to a very high degree on such prey that were temporarily most abundant such as nocturnally swarming males of cumaceans and amphipods. Therefore, the short-term food diversity of the cod was fairly low as compared with those of the other fish species in the area. Larger cods sometimes sleep on the bottom at night. The cod is adapted to feed mainly near the bottom, and for catching prey on and below the bottom surface. It captures prey mainly by suction, but because it is well adapted for seizing and biting, the morphological requirements of which restrict those required for intense suction, it is not perfectly adapted for intense suction. It can swallow large and heavily spined prey in a vigorous way because its oesophagus and stomach are very tough.