Spectral sensitivity and color vision of fish as indicated by S-potential

Preferential incorporation of dark, coloured materials into nests by a mound-nesting stream cyprinid

We compared size and colour characteristics of rocks used by male cutlip minnows Exoglossum maxillingua to build nests to those of streambed background materials. We found that materials used to construct conspicuous, mound-shaped nests were uniform in size and darker and more colour-saturated than background materials of the same size. To our knowledge, this phenomenon is the first reported example of fish selecting nest materials based on colour and has important implications for the conservation of mound-nesting stream cyprinid species.

Protanopia (red color-blindness) in medaka: a simple system for producing color-blind fish and testing their spectral sensitivity

BACKGROUND

Color perception is important for fish to survive and reproduce in nature. Visual pigments in the retinal photoreceptor cells are responsible for receiving light stimuli, but the function of the pigments in vivo has not been directly investigated in many animals due to the lack of color-blind lines and appropriate color-perception tests.

METHODS

In this study, we established a system for producing color-blind fish and testing their spectral sensitivity. First, we disrupted long-wavelength-sensitive (LWS) opsins of medaka (Oryzias latipes) using the CRISPR/Cas9 system to make red-color-blind lines. Single guide RNAs were designed using the consensus sequences between the paralogous LWSa and LWSb genes to simultaneously introduce double-frameshift mutations. Next, we developed a non-invasive and no-prior-learning test for spectral sensitivity by applying an optomotor response (OMR) test under an Okazaki Large Spectrograph (OLS), termed the O-O test. We constructed an electrical-rotary cylinder with black/white stripes, into which a glass aquarium containing one or more fish was placed under various monochromatic light conditions. The medaka were irradiated by the OLS every 10 nm, from wavelengths of 700 nm to 900 nm, and OMR was evaluated under each condition.

RESULTS

We confirmed that the lws ^- medaka were indeed insensitive to red light (protanopia). While the control fish responded to wavelengths of up to 830 nm (λ = 830 nm), the lws ^- mutants responded up to λ = 740 nm; however, this difference was not observed after adaptation to dark: both the control and lws ^- fish could respond up to λ = 820 ~ 830 nm.

CONCLUSIONS

These results suggest that the lws ^- mutants lost photopic red-cone vision, but retained scotopic rod vision. Considering that the peak absorption spectra (λ_max) of medaka LWSs are about 560 nm, but the light-adapted control medaka could respond behaviorally to light at λ = 830 nm, red-cone vision could cover an unexpectedly wide range of wavelengths, and behavioral tests could be an effective way to measure spectral sensitivity. Using the CRISPR/Cas9 and O-O systems, the establishment of various other color-blind lines and assessment of their spectra sensitivity could be expected to proceed in the future.

Pectoral fins aid in navigation of a complex environment by bluegill sunfish under sensory deprivation conditions

Complex structured environments offer fish advantages as places of refuge and areas of greater potential prey densities, but maneuvering through these environments is a navigational challenge. To successfully navigate complex habitats, fish must have sensory input relaying information about the proximity and size of obstacles. We investigated the role of the pectoral fins as mechanosensors in bluegill sunfish swimming through obstacle courses under different sensory deprivation and flow speed conditions. Sensory deprivation was accomplished by filming in the dark to remove visual input and/or temporarily blocking lateral line input via immersion in cobalt chloride. Fish used their pectoral fins to touch obstacles as they swam slowly past them under all conditions. Loss of visual and/or lateral line sensory input resulted in an increased number of fin taps and shorter tap durations while traversing the course. Propulsive pectoral fin strokes were made in open areas between obstacle posts and fish did not use the pectoral fins to push off or change heading. Bending of the flexible pectoral fin rays may initiate an afferent sensory input, which could be an important part of the proprioceptive feedback system needed to navigate complex environments. This behavioral evidence suggests that it is possible for unspecialized pectoral fins to act in both a sensory and a propulsive capacity.

Microspectrophotometric evidence for cone monochromacy in sharks

Sharks are apex predators, and their evolutionary success is in part due to an impressive array of sensory systems, including vision. The eyes of sharks are well developed and function over a wide range of light levels. However, whilst close relatives of the sharks-the rays and chimaeras-are known to have the potential for colour vision, an evolutionary trait thought to provide distinct survival advantages, evidence for colour vision in sharks remains equivocal. Using single-receptor microspectrophotometry, we measured the absorbance spectra of visual pigments located in the retinal photoreceptors of 17 species of shark. We show that, while the spectral tuning of the rod (wavelength of maximum absorbance, λ(max) 484-518 nm) and cone (λ(max) 532-561 nm) visual pigments varies between species, each shark has only a single long-wavelength-sensitive cone type. This suggests that sharks may be cone monochromats and, therefore, potentially colour blind. Whilst cone monochromacy on land is rare, it may be a common strategy in the marine environment: many aquatic mammals (whales, dolphins and seals) also possess only a single, green-sensitive cone type. It appears that both sharks and marine mammals may have arrived at the same visual design by convergent evolution. The spectral tuning of the rod and cone pigments of sharks is also discussed in relation to their visual ecology.

Temporal resolution and spectral sensitivity of the visual system of three coastal shark species from different light environments

Visual temporal resolution and scotopic spectral sensitivity of three coastal shark species (bonnethead Sphyrna tiburo, scalloped hammerhead Sphyrna lewini, and blacknose shark Carcharhinus acronotus) were investigated by electroretinogram. Temporal resolution was quantified under photopic and scotopic conditions using response waveform dynamics and maximum critical flicker-fusion frequency (CFF). Photopic CFF(max) was significantly higher than scotopic CFF(max) in all species. The bonnethead had the shortest photoreceptor response latency time (23.5 ms) and the highest CFF(max) (31 Hz), suggesting that its eyes are adapted for a bright photic environment. In contrast, the blacknose had the longest response latency time (34.8 ms) and lowest CFF(max) (16 Hz), indicating its eyes are adapted for a dimmer environment or nocturnal lifestyle. Scotopic spectral sensitivity revealed maximum peaks (480 nm) in the bonnethead and blacknose sharks that correlated with environmental spectra measured during twilight, which is a biologically relevant period of heightened predation.

Identification of horizontal cells generating different spectral responses in the retina of a teleost fish (Eugerres plumieri)

Six different types of spectral responses were recorded from horizontal cells under mesopic conditions in perfused retina, isolated from the dark-adapted mojarra (Eugerres plumieri). They were tentatively termed photopic Lr-, Lg1-, Lg2-, Lb-, and C-type, and scotopic L-type. The Lr-, Lg-, and Lb-type responses showed a maximum peak at 605, 550, and 516 nm respectively, while the C-type was composed of hyperpolarizing potentials in response to shorter wavelengths and depolarizing potentials in response to longer wavelengths (so-called R/G-type). The scotopic L-type has a peak at 516 nm in the spectral response and a slow decay phase in the waveform response. Following a brief period of diffuse illumination, it was found that the Lg1-type response is altered to the Lr-type, while both Lg2- and Lb-type responses change to the C-type. Intracellular marking with Lucifer or Procion yellow identified the cellular origins of different response types: external (He) and medial horizontal (Hm) cells for the Lr-type, internal horizontal (Hi) cells for the C-type, and rod-horizontal (Hr) cells for the scotopic L-type. Only He cells were found to possess an axon, while dye coupling was seen between axonless Hm, Hi, or Hr cells but not between He cells. The morphology of these fluorescent dye-marked cells was the same as that of the respective cells observed in Golgi-stained materials.

The cellular origin of an unusual type of S-potential: an intracellular horseradish peroxidase study in a cyprinid fish retina

L2-type S-potentials are mainly blue/green-sensitive hyperpolarizing responses with a red-sensitive depolarizing component which is either weak or absent. They were first described in the retina of the roach, a cyprinid fish, by Djamgoz (1978, 1984) and Djamgoz & Ruddock (1978, 1979a). The cellular origin of these responses has been determined and characterized by intracellular recording, horseradish peroxidase staining, and light and electron microscopy. They were found to arise in horizontal cells with H2-like morphologies on average (Stell & Lightfoot, 1975). The dendrites of these cells contacted green- and blue-sensitive cone pedicles within which both lateral and central contacts were made at ribbon synapses. The laterally-positioned dendrites had incompletely formed spinules associated with them. A number of similarities between these units and the biphasic, chromaticity (Cb)-type S-potentials have been outlined and it is suggested that L2 units are essentially Cb-units with a weak depolarizing component. In turn, it is suggested that the depolarizing component is reduced as a consequence of the relatively dark-adapted states of the retinae. It is concluded that the negative feed-back pathway that subserves the generation of depolarizing (Cb-type) S-potentials is weak or absent in dark-adapted retinae and that spinules may be the site of this feed-back interaction.

Electrophysiological characterization of the spectral sensitivities of horizontal cells in cyprinid fish retina

The spectral characteristics of horizontal cells of roach retina have been studied by a multi-disciplinary approach. Intracellular recording was combined with localized irradiation of the retina with spectrally selective laser beams to facilitate quantitative analyses. L1HC's were driven mainly by red (R)--sensitive cones. CbHC's were depolarized by R- and hyperpolarized by green (G)--and blue (B)--sensitive cones. The hyperpolarizing responses of L2HC's were also driven by B-, and G-sensitive cones, and, in addition, some depolarized to a 675 nm test stimulus. L2 units were relatively more abundant in dark-adapted retinae; during light adaptation, they became progressively less abundant. It is suggested that the spectral characteristics of some HC's are influenced by the adaptational state of the retina.

Color-specific interconnections of cones and horizontal cells in the retina of the goldfish

In Golgi preparations of goldfish retina we have observed three types of horizontal cell which receive exclusively from cones and one which receives exclusively from rods. The cone horizontal cells were designated H1, H2 and H3, in order of increasing dendritic spread, increasing separation from the outer synaptic layer, decreasing size of perikaryon, and decreasing density of cone contacts. Slender appendages with knobby terminal enlargements project horizontal cells by alalyzing serial 1 mum sections with the light microscope. The probable inputs, in terms of visual pigments in the cones which contact them, are: H1, red+green+blue; H2, green+blue; H3, blue. Analysis of previously published work suggests (1) that H1 cells generate monophasic or L-type responses, H2 cells generate biphasic or C1-type responses, and H3 cells generate triphasic or C2-type responses; (2) that H1 cells receive direct functional input at least from red-sensitive cones, H2 cells from green-sensitive cones, and H3 cells from blue-sensitive cones, and (3) that H1 constitute pathways from cones to H2 cells, and H2 cells, and H2 cells constitute pathways from cones and H1 cells to H3 cells. The precise location and route of the transfers, from H1 to H2 and from H2 to H3, are not yet known.