Light-specific wavelengths differentially affect the exploration rate, opercular beat, skin color change, opsin transcripts, and the oxi-redox system of the longsnout seahorse Hippocampus reidi.

Light is a strong stimulus for the sensory and endocrine systems. The opsins constitute a large family of proteins that can respond to specific light wavelengths. Hippocampus reidi is a near-threatened seahorse that has a diverse color pattern and sexual dimorphism. Over the years, H. reidi's unique characteristics, coupled with its high demand and over-exploitation for the aquarium trade, have raised concerns about its conservation, primarily due to their significant impact on wild populations. Here, we characterized chromatophore types in juvenile and adult H. reidi in captivity, and the effects of specific light wavelengths with the same irradiance (1.20 mW/cm2) on color change, growth, and survival rate. The xanthophores and melanophores were the major components of H. reidi pigmentation with differences in density and distribution between life stages and sexes. In the eye and skin of juveniles, the yellow (585 nm) wavelength induced a substantial increase in melanin levels compared to the individuals kept under white light (WL), blue (442 nm), or red (650 nm) wavelengths. In addition, blue and yellow wavelengths led to a higher juvenile mortality rate in comparison to the other treatments. Adult seahorses showed a rhythmic color change over 24 h, the highest reflectance values were obtained in the light phase, representing a daytime skin lightening for individuals under WL, blue and yellow wavelength, with changes in the acrophase. The yellow wavelength was more effective on juvenile seahorse pigmentation, while the blue wavelength exerted a stronger effect on the regulation of adult physiological color change. Dramatic changes in the opsin mRNA levels were life stage-dependent, which may infer ontogenetic opsin functions throughout seahorses' development. Exposure to specific wavelengths differentially affected the opsins mRNA levels in the skin and eyes of juveniles. In the juveniles, skin transcripts of visual (rh1, rh2, and lws) and non-visual opsins (opn3 and opn4x) were higher in individuals under yellow light. While in the juvenile's eyes, only rh1 and rh2 had increased transcripts influenced by yellow light; the lws and opn3 mRNA levels were higher in juveniles' eyes under WL. Prolonged exposure to yellow wavelength stimulates a robust increase in the antioxidant enzymes sod1 and sod2 mRNA levels. Our findings indicate that changes in the visible light spectrum alter physiological processes at different stages of life in H. reidi and may serve as the basis for a broader discussion about the implications of artificial light for aquatic species in captivity.

Evidence of feminization in seahorses from a tropical estuary.

Intersex has been reported regularly in wild populations of gonochoristic fish. The authors investigated the possible feminization of seahorses in a population of Hippocampus reidi in Brazil, as well as report a case of a brood pouch reduction after reproductive stimuli. The female seahorses of this population showed two kinds of morphological anomalies. The proportion of the animals affected in the study population was consistent and was uncorrelated with the sex ratio. The study indicates the changes in the sexual profile of the individual.

Field studies of a Brazilian seahorse population, Hippocampus reidi Ginsburg, 1933

This study was carried out to fill the gaps that remain under Hippocampus reidi biology. Analysis of variations of sex ratio, density, breeding season, distribution and home range of a population of the endangered Brazilian seahorse H. reidi from a rocky shore on Araçatiba beach, Ilha Grande, Brazil were carried out. Araçatiba beach is a tourist Environmental Protected Area, suffering antropic pressure. A fixed population of H. reidi was studied, where al lthe individuals were visually tagged and sex, reproductive state and location on site were identified from December 2002 to November 2004. A total of 20 individuals were visually tagged with a mean density of 0.18 m-2. Sex ratios were skewed, with more females than males. All the males brooded during 13 months and presented smaller home range than the females during the breeding season. The highest densities were found on shallowest areas.

Este estudo foi realizado com o objetivo de preencher algumas lacunas sobre a biologia natural de Hippocampus reidi. Foram analisadas as variações na proporção sexual e densidade, período reprodutivo, distribuição e área de deslocamento de uma população do cavalo marinho brasileiro ameaçado de extinção Hippocampus reidi de um costão rochoso da praia de Araçatiba, Ilha Grande, Brasil. A praia de Araçatiba é uma Área de Proteção Ambiental turística, a qual sofre com a pressão antropogênica. Foi estudada uma população fixa de H. reidi, sendo que todos os indivíduos foram marcados visualmente e foram determinados o sexo, o período reprodutivo e a localização na área de novembro de 2002 a novembro de 2004. Um total de 20 indivíduos foram marcados com uma densidade média na área de 0,18 m-2. A proporção sexual variou de forma alternada com maior número de fêmeas que de machos. Durante 13 meses todos os machos encontrados estavam incubando. Os cavalos marinhos apresentaram área de deslocamento menor que as fêmeas durante o período reprodutivo. As maiores densidades foram encontradas em áreas mais rasas da área de estudo.