Search

The present study examines the feeding habits ofAlepocephalus rostratus, the only species of the family Alepocephalidae in the Mediterranean Sea and the second most important fish species, in terms of biomass, inhabiting the deep slope of the Catalan Sea. Samples were obtained at depths between 1000–2250 m. Diet was analysed for two different size-classes (immature and mature specimens) at three different bathymetric strata during two different seasons. The feeding habits ofA. rostratusincluded a narrow range of mobile macroplanktonic organisms (e.g.Pyrosoma atlanticumandChelophyes appendiculata)and some material of benthic origin.Pyrosoma atlanticumwas the preferred prey item in spring at 1000–1425 m, being very scarce in summer at the same depth as a consequence of its scarcity in the environment during this season. There were some ontogenic differences in the diet ofA. rostratusat 1425–2250 m. Adults ingested more and larger prey than juvenile specimens. The scarcity of resources below 1200–1400 m fostered a more diversified diet, as well as passive predation of sedimented material.

The demersal ichthyofauna of the continental slope of the Porcupine Seabight, eastern North Atlantic, was studied from 144 samples taken by three different types of otter trawl. At least 118 species from 43 families were represented among some 54,000 specimens collected from 247 to 2172m soundings. Collectively, the catches were dominated in species richness by the Macrouridae, Alepocephalidae and Squalidae and in abundance by the Synaphobranchidae, Macrouridae and Moridae. Separately, relative abundance of species was more similar between the two larger trawls, setting their catches apart from the smaller net. Gear selectivity evidently accounted for this variation, which was examined by an index we developed and call species fidelity. This accounts for patterns of continuous faunal change with increased soundings concomitant with variance in species adult size and mobility. In pursuance of a more accurate representation of relative biomass and abun-dance than achieved hitherto, the best estimate, within the limitations imposed by the sampling gears and regime, was derived from a combination of the mean values per 200m stratum of the two large trawls with the addition of those of the eel, Synaphobranchus kaupi, from the small gear. Tentative comparisons between these results and those from elsewhere suggest that the Porcupine Seabight is generally lower in biomass and similar or lower in abundance. It was concluded that an accurate indication of ichthyofaunal structure with increased soundings can only be achieved through a detailed knowledge of the size structure of each species over its entire sounding range synthesized from a multi-trawl investigation via analyses of species fidelity.

Alepocephalus bairdii is a deep sea fish caught but discarded by semi-industrial fisheries from the north-east Atlantic Ocean. Reproductive features were investigated on 448 females of 29–93 cm standard length (SL) captured over 2 y (December 1995–December 1997) at 800–1280 m off the west coast of the British Isles. The first maturity of females was determined at L50=55 cm SL. A well-defined spawning period could not be determined in this species; a batch spawner characterized by an indeterminate annual fecundity. Absolute batch fecundity was estimated between 458 and 7049 oocytes per female 63–88 cm SL.

In the family Alepocephalidae there areca. 19 valid genera (Markle, personal communication). Whilst luminescence has never been observed, there are four genera,Xenodermichthys, Photostylus, RouleinaandMicrophotolepis, which contain species bearing structures that have been interpreted anatomically as photophores (Herring & Morin, 1978). Among these four there is a remarkable diversity of photophore structure. The photophores ofXenodermichthysandPhotostylusare similar in having well developed central cores (reddish violet inXenodermichthys) and reflector layers, yet those ofXenodermichthysare sessile whilst those ofPhotostylusare borne on stalks (e.g. von Lendenfeld, 1887; Best & Bone, 1976). Not all species ofRouleinahave light organs but where they are present they are sessile. Photophore structure ofRouleinahas been examined only inR. maderensisMaul and was found there to be rather degenerate in adults (Markle, 1978). The light organs ofMicrophotolepis multipunctataSazanov and Parin differ yet again in being scale covered, which contrasts with the naked photophores in the other three genera (Sazanov & Parin, 1977). The abundance and distribution of photophores in adults also varies with genus and species. Thus inMicrophotolepisandXenodermichthysthey are extremely numerous and regularly arranged but inPhotostylusthey are few and less ordered (Günther, 1887; Beebe, 1933; Sazanov & Parin, 1977). In different species ofRouleinaphotophores may be relatively abundant and regularly arranged or few in number without such regular pattern (Maul, 1948; Uyeno & Kishida, 1977; Markle, 1978).