The ichthyoneuston of Galway Bay (west of Ireland). II. Food of post-larval and juvenile neustonic and pseudo-neustonic fish

O Tully, PÓ Ceidigh
1989 Marine Ecology Progress Series  
Stomach contents of 5 species of neustonic (Ciliata septentrionalis, CiLiata mustela, Gaidropsaurus mediterraneus, Rhinonemus cimbrius, Scophthalmus maximus) and 4 species of pseudoneustonic (Pollachius pollachius, Pollachius virens, Medangius merlangus, Cyclopterus lumpus) post-larval and juvenile fish, caught in the neustal and the immediate sub-surface layer, were examined to compare diets and food consumption. Fish length ranged from 5 to 39 mm. The diets of Ciliata spp. were dominated by
more » ... sh eggs and calanoid copepods. G. mediterraneus and R. cimbrius ate mainly copepods and Cladocera. Oikopleura spp., copepods and Podon spp. dominated in S. maximus. In the pseudoneustonic Pollachius spp., Acartia spp. and Calanus spp. were most important while M. merlangus preyed almost totally on copepods. C. lumpus, which associated with driftweed, specialised on harpacticoid copepods and crab megalopae. Dietary differences among species 5 mm length groups were investigated by step-wise discriminant analysis. The analysis isolated 17 diet categories which were significant in discriminating the diets of 5 mm length groups of 5 species (C. septentrionalis, C. mustela, P, pollachius, P. virens, M. me]-langus) caught mainly during May and June. Ciljata groups were dlstinct from those of other species and their diets changed gradually as fish increased in length. Fish eggs were less important in larger fish which preyed more on fish larvae, crab megalopae and harpacticoid copepods. Five diet categories were significant in discriminating the diets of 5 mm length groups of species caught mainly during autumn (G. mediterraneus, R. cimbrius, S. maximus, C. lumpus). The diets of S. maximus and C. lumpus changed abruptly when fish reached 20 mm in length. C. lumpus switched from harpacticoid copepods to crab megalopae and S. maximus switched from Podon spp. to fish larvae and Oikopleura spp. Podon spp, were important in larger size groups of G. mediterraneus and R. cimbdus. Discriminant analysis did not find significant differences between the diets of smaller length groups of these 2 species. Die1 variation in stomach fullness of C. mustela and G. mediterraneus showed that feeding occurred only during daylight. In all species except G. rnediterraneus and S. n~aximus larger fish ate a greater number of prey than smaller fish. C. mustela over 25 mm, P. pollachius and M. merlangus over 15 mm and C. lumpus and S. maximus over 20 mm also had fuller stomachs than smaller fish. Stomach fullness was higher in neustonic than in pseudoneustonic species. Because of this, it is suggested that feeding conditions at the surface are unique and that neuston~c species have adaptations that enable them to feed more successfully in this environment.
doi:10.3354/meps051301 fatcat:sey2ahmz7nellp3wkqcd53ury4