The nighttime distribution of vertically migrating mesopelagic fish in relation to nocturnal light was studied during a circumglobal survey, in the Red Sea, and in a fjord at high latitude. The study was based on data derived from ship borne echo sounders (circumglobal and the Red Sea) as well as using upward looking echo sounders mounted on the bottom (Masfjorden, Norway). We also applied a numerical model for analyzing diel vertical migration patterns. The effect of the lunar cycle was the focus in studies at low latitudes, while seasonal changes in nocturnal light climate was in focus at high latitude. Lunar phase significantly affected the distribution of mesopelagic fish at the global scale and in the Red Sea. During nights near full moon, scattering layers of mesopelagic fish distributed deeper than during darker phases of the moon. At high latitude, mesopelagic fish switched its behavior along with seasonal changes in nocturnal lights. In autumn, the population of the studied fish (Maurolicus mueleri) formed separated layers. Juveniles performed normal diel vertical migration followed by midnight sinking, with midnight sinking mainly related to temperature minima and also for avoiding predators. Meanwhile the adults did not migrate vertically, reducing foraging but increasing the adult survival. From late winter to mid-Spring, interrupted ascents behavior was noted in the afternoon. Predator avoidance, satiation, and finding temperature optimum might be the reason behind interrupted ascents. At lighter nights in mid-summer, M. muelleri took on schooling behavior, likely as an anti-predator behavior permitting access to the upper waters in the absence of darkness.

A distribuição horizontal e vertical das larvas de peixes mesopelágicos de Phosichthyidae foi descrita a partir de dados amostrados desde a superfície até 200 m de profundidade, e em 5 estratos na coluna de água. As coletas foram realizadas no verão e inverno de 2002, em radiais perpendiculares à costa Sudeste do Brasil, entre o cabo de São Tomé (RJ) e a ilha de São Sebastião (SP). A abundância das larvas (larvas.m²) foi estimada para o material amostrado pela rede Bongô (333 cm) e a densidade (larvas.m³) para a Multi Plankton Sampler (300 cm). No total foram coletadas 538 larvas de Phosichthyidae no verão e 146 no inverno. Duas espécies foram identificadas, Pollichthys mauli e Vinciguerria nimbaria, ambas apresentaram-se distribuídas, preferencialmente, na região oceânica da área de estudo com maiores densidades entre 60 e 80 m de profundidade, onde a temperatura e a salinidade foram superiores a 20°C e 36, respectivamente, estando diretamente relacionados à massa de Água Tropical, transportada pela Corrente do Brasil. Todas as fases de desenvolvimento larval foram capturadas, entretanto, a maioria das larvas estava em pós-flexão da notocorda. Em relação à variação diária, as larvas foram mais abundantes durante a noite. / Horizontal and vertical distribution of mesopelagic Phosichthyidae fish larvae was described based on data sampled collected from the surface up to 200 m depth, and at five stratums on the water column. The sampling was performed in summer and winter, 2002, on perpendiculars transects in southeastern Brazilian Bight, between São Tomé Cape (RJ) and São Sebastião Island (SP). The abundance of larval (larvae.m²) was estimated from sample of Bongo net (333 cm) and the density (larvae.m³) from sample of Multi Plankton Sampler (300 cm). A total of 538 larvae of Phosichthyidae was collected during summer, and 146 in the winter. Two species, Pollichthys mauli and Vinciguerria nimbaria, were identified; both were mainly distributed in the oceanic region of the study area and were more abundant between 60 and 80 m depth, where temperature and salinity were higher than 20°C and 36, respectively, which are directly related with the Tropical Water mass, transported by Brazil Current. All larval stages of development were caught, however, the majority was in postflexion stage. In relation to diel variation, larvae were more abundant during the night.

A distribuição horizontal e vertical das larvas de peixes mesopelágicos de Phosichthyidae foi descrita a partir de dados amostrados desde a superfície até 200 m de profundidade, e em 5 estratos na coluna de água. As coletas foram realizadas no verão e inverno de 2002, em radiais perpendiculares à costa Sudeste do Brasil, entre o cabo de São Tomé (RJ) e a ilha de São Sebastião (SP). A abundância das larvas (larvas.m²) foi estimada para o material amostrado pela rede Bongô (333 cm) e a densidade (larvas.m³) para a Multi Plankton Sampler (300 cm). No total foram coletadas 538 larvas de Phosichthyidae no verão e 146 no inverno. Duas espécies foram identificadas, Pollichthys mauli e Vinciguerria nimbaria, ambas apresentaram-se distribuídas, preferencialmente, na região oceânica da área de estudo com maiores densidades entre 60 e 80 m de profundidade, onde a temperatura e a salinidade foram superiores a 20°C e 36, respectivamente, estando diretamente relacionados à massa de Água Tropical, transportada pela Corrente do Brasil. Todas as fases de desenvolvimento larval foram capturadas, entretanto, a maioria das larvas estava em pós-flexão da notocorda. Em relação à variação diária, as larvas foram mais abundantes durante a noite. / Horizontal and vertical distribution of mesopelagic Phosichthyidae fish larvae was described based on data sampled collected from the surface up to 200 m depth, and at five stratums on the water column. The sampling was performed in summer and winter, 2002, on perpendiculars transects in southeastern Brazilian Bight, between São Tomé Cape (RJ) and São Sebastião Island (SP). The abundance of larval (larvae.m²) was estimated from sample of Bongo net (333 cm) and the density (larvae.m³) from sample of Multi Plankton Sampler (300 cm). A total of 538 larvae of Phosichthyidae was collected during summer, and 146 in the winter. Two species, Pollichthys mauli and Vinciguerria nimbaria, were identified; both were mainly distributed in the oceanic region of the study area and were more abundant between 60 and 80 m depth, where temperature and salinity were higher than 20°C and 36, respectively, which are directly related with the Tropical Water mass, transported by Brazil Current. All larval stages of development were caught, however, the majority was in postflexion stage. In relation to diel variation, larvae were more abundant during the night.