Midwater fishes in the eastern North Atlantic—I. Vertical distribution and associated biology in 30°N, 23°W, with developmental notes on certain myctophids

摘要: Abstract This paper is the first of a series describing vertical distribution midwater fishes in eastern North Atlantic areas approximately 10° latitude apart near 20° meridian. As such, it concerned solely with collections made 30°N, 23°W. The results are based primarily upon RMT 8 net samples collected using an opening-closing 1+8 combination net. In all, 17,443 specimens were caught by 8, divisible into 37 families, 66 genera 98 species identified. Numerically most abundant groups recognized Gonostomatidae (60% total catch), Macrorhamphosidae (23%) and Myctophidae (7%). Some definition limits provided for majority represented, but only 31 considered detail. Where possible, observed biological phenomena (e.g. development, sexual maturity, dimorphism, etc.) have been correlated. general, characteristics species' distributions, relations migratory behaviour as one would anticipate from past work. Among many species, size-depth stratification was observed, migrants, appeared dependent developmental state. mode however, had no bearing ultimate behaviour. Certain non-migratory elements population habitually migrant e.g. Chauliodus danae, could not be satisfactorily interpreted basis factors examines. Migrant principally occupied 400–900 m depth day, 25–300 night, although they occurred at greater depths. Reverse migrations Macrorhamphosus. overall catches dominated non-migrants, depths that 200 these comprised per all times. Cyclothone constituted genus sampled greatest insight distributional C. braueri, numerous probably single spawner, demonstrate may correlated maturity stages. olfactory structure males more complicated than previously described. larger develop snout prolongation which improve water flow through nasal rosette hence olfaction. Unlike microdon, braueri does undergo sex-reversal. Developmental notes included myctophid Notoscopelus resplendens, Benthosema suborbitale, Hygophum hygomi Appendix.