Changes in adrenergic innervation to chromatophores during prolonged background adaptation in the medaka, Oryzias latipes

The Effect of Background Color on Skin Color Variation of Juvenile Plectropomus leopardus

Fish skin color is usually strongly affected by the background color of their environment. The study investigated the effects of five different background colors on the skin color of leopard coral groupers (Plectropomus leopardus). More than 450 juveniles were reared in Blue, Red, Black, White, and Transparent background tanks for 56 days. The paraffin section showed that the skin melanin zone of fish in the White group was smaller, whereas the Black and Red groups (especially Black) were nearly the largest. The apparent skin color of P. leopardus was red on the white background, which darkened in response to the other color backgrounds. The Black group revealed the blackest skin color, followed by the transparent group. Moreover, the White group had the highest L*, a*, and b* values. The melanin content and tyrosinase activity in the dorsal and ventral skin of the Black group were significantly higher than those in the other groups (p < 0.05), and the serum α-MSH level was higher in the Black group as well. The carotenoid and lutein contents showed completely different trends among the experimental groups, as carotenoid content was higher in the Red and White groups, while lutein content was higher in the Transparent group. The expression level of scarb1 was highest in the Blue and White groups, followed by the Transparent group, and lowest in the Black group (p < 0.05). The expression trend of scarb1 was similar to the skin color in different backgrounds, indicating that the background color regulated scarb1 expression level through visual center, then influenced the uptake and transport of carotenoids, then influenced the skin color formation of P. leopardus. Moreover, lighter colors inhibited the formation of melanocytes and had a significant effect on carotenoid and lutein contents. Pigment-related genes were involved in the regulation of fish skin color, and they were affected by background color in P. leopardus. These results indicate that a white background is more conducive to maintaining red skin color in juvenile P. leopardus.

Colour changes in Labeo rohita (Ham.) due to pigment translocation in melanophores, on exposure to municipal wastewater of Tung Dhab drain, Amritsar, India

The present study was aimed to evaluate the effect of municipal wastewater of Tung Dhab drain on morphology of scale melanophores in freshwater fish Labeo rohita (Ham.). Chronic, non-renewal toxicity tests were performed with sub lethal concentrations (17.7, 26.6 and 35.4%) of wastewater for exposure durations of 15, 30 and 60 days. Recovery experiments were also performed for duration of 60 days. The scales were removed, processed and diameters of melanophores were measured using an ocular micrometer. The results showed concentration and duration dependent changes in melanophore morphology (size and dendricity) in experimental fish as compared to control fish. The values of mean melanophore size index (MMSI) varied from 5.37 ± 0.49 (17.7%) to 12.12 ± 0.81 (35.5%) in comparison to control values of 4.32 ± 0.32 and 4.55 ± 0.29 for 15 and 60 days respectively. The recovery experiments suggested that observed dark colouration due to pigment translocation is reversible, even after chronic exposure for 60 days.

Possible involvement of cone opsins in distinct photoresponses of intrinsically photosensitive dermal chromatophores in tilapia Oreochromis niloticus

Dermal specialized pigment cells (chromatophores) are thought to be one type of extraretinal photoreceptors responsible for a wide variety of sensory tasks, including adjusting body coloration. Unlike the well-studied image-forming function in retinal photoreceptors, direct evidence characterizing the mechanism of chromatophore photoresponses is less understood, particularly at the molecular and cellular levels. In the present study, cone opsin expression was detected in tilapia caudal fin where photosensitive chromatophores exist. Single-cell RT-PCR revealed co-existence of different cone opsins within melanophores and erythrophores. By stimulating cells with six wavelengths ranging from 380 to 580 nm, we found melanophores and erythrophores showed distinct photoresponses. After exposed to light, regardless of wavelength presentation, melanophores dispersed and maintained cell shape in an expansion stage by shuttling pigment granules. Conversely, erythrophores aggregated or dispersed pigment granules when exposed to short- or middle/long-wavelength light, respectively. These results suggest that diverse molecular mechanisms and light-detecting strategies may be employed by different types of tilapia chromatophores, which are instrumental in pigment pattern formation.

Morphological color changes in fish: Regulation of pigment cell density and morphology

Pigment cells enable fish to change their coloration. It has been recognized that fish color changes can be divided into two categories; one is a physiological color change, which is attributed to rapid motile responses of chromatophores, and the other is a morphological color change, which results from changes in the morphology and density of chromatophores. Long-term adaptation of fish to a certain background can be a general cue to morphological color changes, and has been studied from the beginning of the 19th century. Although the motile mechanism and its control in fish chromatophores are now being elucidated, it is not yet clear how chromatophores change their density and what controls morphological color changes. In recent years, chromatophores, especially melanophores, have been shown to differentiate and to die by apoptosis under the influence of factors that regulate motile responses. Those factors are likely to utilize common intracellular signaling pathways used in part to regulate both types of color changes. In this article, after briefly reviewing the history of early studies, recent findings are discussed relevant to increases or decreases in chromatophores, and changes in their morphology. Finally, morphological color changes are discussed as physiological phenomena involved in the balance between differentiation and apoptosis of chromatophores.

Specialised sympathetic neuroeffector associations in rat iris arterioles

Vascular sympathetic neuroeffector associations have been examined in rat iris arterioles using serial section electron microscopy and reconstruction techniques. Examination of random sections showed that, of all profiles of varicosities (199) seen to lie closer than 4 microns to vascular smooth muscle cells, only a small proportion (29/199) were found in close association with vascular smooth muscle cells, where adjacent membranes were separated by less than 100 nm. However, serial section examination, from intervaricose region to intervaricose region, of 79 varicosities similarly observed lying within 4 microns of vascular smooth muscle cells showed that 54 formed close associations with vascular smooth muscle cells. In serial sections, all these varicosities were also closely associated with melanocytes and of the 25 remaining varicosities, 22 formed close associations with melanocytes alone, whilst 3 did not come into close association with any effector cell. The increased observation of close associations with vascular smooth muscle cells in serial sections, compared with random sections, is consistent with the demonstration that the area of contact only occupies, on average, a small percentage (5%) of the total surface area of the varicosity as seen in the 3-dimensional reconstructions. In both random and serial sections, close associations were observed between varicosities and vascular smooth muscle cells or melanocytes irrespective of whether fibres were present singly or in small nerve bundles. Three-dimensional reconstruction of associations of varicosities and vascular smooth muscle cells demonstrated several common features, such as accumulations of synaptic vesicles and loss of Schwann cell covering at the region of membrane facing the effector cell. The similarity in the appearance of the neuroeffector association seen in this study and those described in previous studies provides evidence for the existence of a common sympathetic neuroeffector association, irrespective of the receptor subtype involved in neurotransmission.

Regulation of melanophore responsiveness in the background-adapted medaka, Oryzias latipes: change in the intracellular signaling system

The responsiveness of melanophores of the medaka fish (wild type, Oryzias latipes) to a neurotransmitter and hormones is changed differentially after long-term adaptation to a black or white background. In the present study, we further examined whether this phenomenon involved some change in the intracellular signaling system. Using a permeabilized melanophore model, in which pigment granules could be dispersed by exogenously applied cAMP, the requirement of cAMP for pigment-dispersing reaction was revealed to be higher in melanophores of fish adapted to a black background (B cells) than in those of white background-adapted fish (W cells). Specific inhibitors of cAMP-dependent protein kinase (PKA) and cyclic nucleotide phosphodiesterase did not reduce the difference in the pigment dispersion level between B and W cells. A similar result was obtained with the free catalytic subunit of PKA. In contrast, the inhibition of protein phosphatase activity by okadaic acid diminished the difference in the responsiveness between B and W cells. These results suggest that the activity of protein phosphatase in B cell is higher than that in W cells, and that the change in the melanophore responsiveness by long-term chromatic adaptation to a background involves the change in the enzyme activity in the intracellular signaling system.