Multiple Approaches to the Trophic Role of Mesopelagic Fish around the Iberian Peninsula.

Myctophids, commonly vertical migrators, and partial and non-migrant stomiiforms constitute most of the mesopelagic biomass, and transport organic matter throughout the food web from the surface to the ocean's depths. Both the diet and trophic structure of twenty-nine species of mesopelagic fish collected around the Iberian Peninsula were studied through the analysis of stomach contents, quantifying food items with a high taxonomic resolution. The investigation covered oligotrophic to productive habitats, with sampling stations distributed in five discrete zones of the western Mediterranean Sea and the northeastern Atlantic Ocean. The geographic environmental conditions, migratory behavior, and species-specific body sizes allowed for the identification of some major feeding patterns for these fish communities. The trophic niche of migrant myctophids showed a high overlap, with copepods as the primary prey category. The diet composition of generalist myctophids (e.g., Ceratoscopelus maderensis and Hygophum benoiti) reflected the distinct zooplanktonic communities between zones. Large stomiiforms (Chauliodus spp., Sigmops elongatus) preferred feeding on micronekton, while the smallest stomiiforms (e.g., Argyropelecus spp., Cyclothone spp., Vinciguerria spp.) preyed on copepods and ostracods. Given the relevance of the mesopelagic fish communities for commercially exploited species and, therefore, for maintaining the sustainability of the fisheries' activity in the zones analyzed, the information provided in the present study is essential for a better understanding of the biology and ecology of these species.

Plasticity in the shape and growth pattern of asteriscus otolith of black prochilodus Prochilodus nigricans (Teleostei: Characiformes: Prochilodontidae) freshwater Neotropical migratory fish

Using morphometric measurements and wavelets functions, the asterisci otoliths of curimatã, Prochilodus nigricans were analysed to identify the variation in shape and growth increment of individuals from Solimões, Japurá and Negro rivers of the Amazon basin, Brazil. The morphometric and morphological analyses did not reveal evidences of population segregation among rivers, but variations were found in the estimation of otolith growth increment. Also, the otolith shape showed a high variability between individuals, identifying four morphotypes. Morphotype 1 shows a more oval shape with a posterior zone clearly rounded; Morphotype 2 shows the posterior zone rounded, but the anterior end is more elongated; Morphotype 3 shows a completely different shape, elliptic-pentagonal and Morphotype 4 shows the posterior zone rounded, but the anterior end is more elongated and it is the pattern with antirostrum and rostrum more pointed and a deep notch. Therefore, the otolith shape exhibited a phenotypic plasticity that it was not associated with the metabolism of otolith growth. Whereas the otolith shape indicated a homogeneity in the sound perception through Amazon basin, the growth rates revealed an adaptive mechanism to environmental conditions or migratory process of this species.(AU)

Medidas e funções wavelets dos otólitos asteriscus de curimatã, Prochilodus nigricans foram analisados para identificar a variação da forma e do incremento de crescimento dos indivíduos dos rios Solimões, Japurá e Negro da bacia Amazônica, Brasil. As análises morfométricas e morfológicas não revelaram evidências de segregação populacional entre os rios, mas foram encontradas variações na estimativa do incremento do crescimento dos otólitos. Além disso, a forma do otólito mostrou uma alta variabilidade entre os indivíduos, identificando quatro morfotipos. O Morfotipo 1 mostra uma forma mais oval, com zona posterior levemente arredondada; Morfotipo 2 mostra a zona posterior arredondada, mas a extremidade anterior é mais alongada; Morfotipo 3 mostra uma forma completamente diferente, elíptico-pentagonal e Morfotipo 4 mostra a zona posterior arredondada, mas a extremidade anterior mais alongada e ele tem padrão com antirostrum e rostrum mais pontiagudos e abertura profunda. Portanto, a forma do otólito exibiu uma plasticidade fenotípica que não foi associada ao metabolismo do crescimento do otólito. No entanto a forma do otólito indicou uma homogeneidade através da percepção do som na bacia Amazônica, e as taxas de crescimento revelaram um mecanismo adaptativo às condições ambientais ou ao processo migratório da espécie.(AU)