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A full-length complementary (c) DNA encoding ultraviolet ( UV)-sensitive opsin ( sws1) was isolated from the retina of the Japanese sardine Sardinops melanostictus. The sws1 phylogenetic tree showed a sister group relationship with the Cypriniformes, following the ray-finned fish phylogeny. By expressing reconstituted opsin in vitro, it was determined that the maximum absorbance spectrum ( λmax) of sws1 is around 382 nm, being intermediate in position between two subtypes of sws1 pigment that are UV sensitive ( λmax = 355-380 nm) and violet sensitive ( λmax = 388-455 nm), which have been reported to date. The ocular media transmitted >20% transmittance of light in the range of 360-600 nm. In situ hybridization analyses revealed that sws1 messenger (m) RNA is localized in a central single cone surrounded by four double cones in a square mosaic. The square mosaic occupies the ventro-temporal quadrant of the retina and the in situ hybridization signals were dominant in this area suggesting that the fish may use UV vision when looking upward. Based on these results, considerable significances of potential UV sensitivity, in relation to characteristic habits of S. melanostictus, are discussed. [ABSTRACT FROM AUTHOR]

The self-feeding rhythms of rainbow troutOncorhynchus mykissand white-spotted charrSalvelinus leucomaeniswere studied when group-held fishes( n = 10 per group) were fed using self-feeders under two different light intensities(50 lx, 16 μW cm−2 and 700 lx, 215 μW cm−2) during the light phase of the light-dark cycle. Food wastage was also measured. At 50 lx, all groups of rainbow trout learned to operate the self-feeder within 4 days, whereas it took up to 25 days for all groups at 700 lx. In contrast, all groups of white-spotted charr learned self-feeding within 17 days, irrespective of light intensity. These results, although non-significant, suggest that lower light intensities can stimulate instrumental learning in rainbow trout, but not white-spotted charr. In rainbow trout, the total number of trigger actuations for the entire experimental period was significantly higher at 50 rather than 700 lx, although this may have been related to delayed learning at 700 lx. There was no significant effect in white-spotted charr. Growth rate(assessed using the thermal growth coefficient) was also higher in rainbow trout but not white-spotted charr at 50 rather than 700 lx, although this difference was non-significant. Light intensity had no significant effect on food wastage in either rainbow trout or white-spotted charr, and it did not appear to affect the proportion of trigger actuations during the light phase. Clear diurnal feeding rhythms were observed in both species and these were classified into four categories: uniform, dawn, dusk and crepuscular. At 50 lx, fish from both species generally fed in temporally localized periods at either dawn and dusk, whilst feeding was predominantly uniform during the light phase at 700 lx. [ABSTRACT FROM AUTHOR]

The photoreceptors regulating photoperiodic gonadal development of ayu,Plecoglossus altivelis, are not known. In this study, we examined whether the gonads of ophthalmectomized and pinealectomized (Ex+Px) ayu respond to short photoperiod. Gonadosomatic index (GSI) and plasma levels of sex steroids were significantly increased in Ex+Px ayu kept under short photoperiod in both males and females. On the other hand, there were no significant increase in GSI and sex steroids in Ex+Px ayu kept under long photoperiod. The histological observation of the gonads revealed that oocytes undergoing final maturation in females and proliferation of germ cells in males were observed only in Ex+Px ayu kept under short photoperiod. Altogether, our results strongly suggest unknown photoreceptive organ regulates photoperiodic gonadal development of ayu. [ABSTRACT FROM AUTHOR]