Aspects of the biology and ecology of anglerfish (Lophius piscatorius, L.) off the west coast of Scotland (I.C.E.S. sub area via)
This thesis aims to contribute to a better knowledge of several aspects of the biology of L. piscatorius, namely biometry, growth and reproduction. The different subjects in this thesis were studied by examining fresh material obtained from commercial landings and research vessel surveys. L. piscatorius presents significant biometric differences between sexes (at 99% level of confidence). Small males are heavier than females of the same size. Conversely, large females are heavier than males of the same size. Attempts to estimate L. piscatorius' age were made using otoliths. Three other hard structures were used to ascertain consistency of the age readings: vertebrae, illicia and teeth. All structures showed seasonal growth increments. However, these growth increments were easier to interpret in vertebrae. Illicia sections were the most difficult structure to interpret. Although all structures chosen presented many sub-annual checks, illicia displayed them more closely than the others; making age readings more difficult. Teeth were considered inadequate for age readings because they may not be permanent structures. The accuracy and precision of age readings in otoliths were not determined; firstly, the real age of each fish was unknown. Secondly, there was no other independent reader to test precision between readers. The age readings in sagittae were validated and indirectly by back calculation, edge formation and marginal growth. The results obtained from age readings in otoliths were used to directly estimate growth parameters for L. piscatorius by sex. The study of the general morphology and histology of the gonads showed that L. piscatorius have unusual gonads. The testes are tubular, and bean shaped in transverse section while ovaries are confluent and form a single, flattened tube.