Abstract--The feeding habits of the Mediterranean spiderfish, Bathypterois mediterraneus, the most abundant fish below 1000 m on the deep slope of the Catalan Sea (western Mediterranean), were studied. Samples were obtained at depths between 1000 and 2250 m. Diet was analyzed for two different size classes (immature and mature specimens) and three different bathymetric strata. The most important food items found were benthopelagic planktonic calanoid copepods. In juveniles from 1800 to 2250 m, benthic tanaidaceans were secondary, whereas in the adults, mysids were secondary. At other depths, there were no secondary prey: calanoid copepods were consumed almost exclusively; other items were very scarce. Adults ingest larger amounts and sizes of prey than juveniles. The scarcity of resources below 1200-1400 m diversified the diet, although it still primarily consisted of elements from the benthopelagic plankton.

The genus Bathypterois Gunther, 1878 comprises a small group of benthic chlorophthalmid species adapted for life in the deep sea. The genus is circumglobal at temperate latitudes (Sulak, 1984a). Two species of Bathypterois are found in the Mediterranean: Bathypterois dubius and Bathypterois mediterraneus (Bauchot, 1962). The presence of a third, Bathypterois grallator, based on underwater photographs, has been suggested by Sulak (1984a). The Mediterranean spiderfish, Bathypterois mediterraneus, is the only endemic species of the genus, and undoubtedly the most abundant in the Mediterranean (Sulak, 1977; Bauchot, 1987).

Some species of the genus Bathypterois, such as Bathypterois dubius, Bathypterois grallator, Bathypterois atricolor, and Bathypterois viridensis, have been observed from submersibles (Church, 1971; Heezen and Hollister, 1971; Saldanha, 1977; Jones and Sulak, 1990; Chave and Mundy, 1994; Chave and Malahoff, 1998). The fish are benthic, rest on the bottom, and touch the sediment with their longest pelvic and caudal rays (Heezen and Hollister, 1971; Saldanha, 1977), while the long pectoral rays are directed forwards over the head (Saldanha, 1977). Pectoral rays are likely used as sensory devices to detect the presence of planktonic prey, by both direct contact and chemoreception (Sulak, 1977).

According to Sulak (1984a), Bathypterois mediterraneus is benthic on the continental slope and rise, at 260-2800 m. However, in the Catalan Sea (western Mediterranean), the species is restricted in its bathymetric distribution to depths greater than 748 m (Stefanescu et al., 1992a, 1994; Morales-Nin et al., 1996). Of the 31 different species of deep-water fish in the Catalan Sea (Stefanescu et al., 1992a), Bathypterois mediterraneus is subdominant between 1000 and 1500 m, and dominant below this depth. At 1000-2250 m Bathypterois mediterraneus is the fourth in importance for biomass of all fish (Stefanescu et al., 1992a). This species aggregates (Stefanescu et al., 1992a; Morales-Nin et al., 1996), contrary to Sulak's (1984a) observation that it is usually solitary, but may aggregate occasionally.

Knowledge of the biology of deep-sea fauna in the Mediterranean is limited. The feeding habits of some deep-water fish and decapod species in the Catalan Sea have been studied recently (Cartes and Sarda, 1989; Carrasson et al., 1992; Cartes and Abello, 1992; Cartes, 1993a, 1993b, 1993e). Information on Bathypterois mediterraneus biology is limited and fragmentary....