Threshold and spectral sensitivity of vision in medaka Oryzias latipes determined by a novel template wave matching method.

We propose a new analytical method for determining the response threshold in electroretinogram (ERG) in which the wave shows a biphasic slow dc-potential shift. This method uses the recorded wave to the highest intensity stimuli in each wavelength tested as a template wave f(t), and it was compared with other recorded waves obtained under lower intensities g(t). Our test recordings in medaka Oryzias latipes were analogous between the template and the compared waveforms, although there were differences in amplitude and time lag (τ, peak time difference) which occurred as a result of the difference in stimulus intensity. Cross-correlation analysis was applied. Based on the obtained cross-correlation function Cfg(τ) in each comparison, τ was determined as the time lag at which the cross-correlation coefficient Rfg(τ) showed the maximum value. Determined thresholds that were based on both the experimenter's visual inspection and this new method agreed well when the adoption condition was set to satisfy R(τ) ≥ 0.7 and τ ≤ 150 ms in scotopic or τ ≤ 120 ms in photopic conditions. We concluded that this "template wave matching method" is a quick and reliable objective assessment that can be used to determine the threshold. This study analyzed ERG recordings in response to 6 kinds of wavelength light stimuli (380 nm to 620 nm) at different photon flux densities. We report the threshold levels and relative spectral sensitivities in scotopic and photopic vision of medaka.

Green light irradiation during sex differentiation induces female-to-male sex reversal in the medaka Oryzias latipes.

This study investigated whether irradiation of a specific light wavelength could affect the sex differentiation of fish. We first found that the photoreceptor genes responsible for receiving red, green, and ultraviolet light were expressed in the eyes of medaka during the sex differentiation period. Second, we revealed that testes developed in 15.9% of genotypic females reared under green light irradiation. These female-to-male sex-reversed fish (i.e. neo-males) showed male-specific secondary sexual characteristics and produced motile sperm. Finally, progeny tests using the sperm of neo-males (XX) and eggs of normal females (XX) revealed that all F1 offspring were female, indicating for the first time in animals that irradiation with light of a specific wavelength can trigger sex reversal.

The Effects of Continuous Acoustic Stress on ROS Levels and Antioxidant-related Gene Expression in the Black Porgy (Acanthopagrus schlegelii).

Hao-Yi Chang, Tzu-Hao Lin, Kazuhiko Anraku, and Yi Ta Shao (2018) Short-term exposure to strong underwater noise is known to seriously impact fish. However, the chronic physiological effects of continuous exposure to weak noise, i.e. the operation noise from offshore wind farms (OWF), remain unclear. Since more and more OWF will be built in the near future, their operation noise is an emerging ecological issue. To investigate the long-term physiological effects of such underwater noise on fish, black porgies (Acanthopagrus schlegelii) were exposed to two types of simulated wind farm noise-quiet (QC: 109 dB re 1 µPa / 125.4 Hz; approx. 100 m away from the wind turbine) and noisy (NC: 138 dB re 1 µPa / 125.4 Hz; near the turbine)-for up to 2 weeks. Measurement of auditory-evoked potentials showed that black porgies can hear sound stimuli under both NC and QC scenarios. Although no significant difference was found in plasma cortisol levels, the fish under NC conditions exhibited higher plasma reactive oxygen species (ROS) levels than the control group at week 2. Moreover, alterations were found in mRNA levels of hepatic antioxidant-related genes (sod1, cat and gpx), with cat downregulated and gpx upregulated after one week of QC exposure. Our results suggest that the black porgy may adapt to QC levels of noise by modulating the antioxidant system to keep ROS levels low. However, such antioxidant response was not observed under NC conditions; instead, ROS accumulated to measurably higher levels. This study suggests that continuous OWF operation noise represents a potential stressor to fish. Furthermore, this is the first study to demonstrate that chronic exposure to noise could induce ROS accumulation in fish plasma.

Differentiation of visual spectra and nuptial colorations of two Paratanakia himantegus subspecies (Cyprinoidea: Acheilognathidae) in response to the distinct photic conditions of their habitats.

BACKGROUND: Vision, an important sensory modality of many animals, exhibits plasticity in that it adapts to environmental conditions to maintain its sensory efficiency. Nuptial coloration is used to attract mates and hence should be tightly coupled to vision. In Taiwan, two closely related bitterlings (Paratanakia himantegus himantegus and Paratanakia himantegus chii) with different male nuptial colorations reside in different habitats. We compared the visual spectral sensitivities of these subspecies with the ambient light spectra of their habitats to determine whether their visual abilities correspond with photic parameters and correlate with nuptial colorations. RESULTS: Theelectroretinogram (ERG) results revealed that the relative spectral sensitivity of P.h. himantegus was higher at 670 nm, but lower at 370 nm, than the sensitivity of P. h. chii. Both bitterlings could perceive and reflect UV light, but the UV reflection patterns differed between genders. Furthermore, the relative irradiance intensity of the light spectra in the habitat of P. h. himantegus was higher at long wavelengths (480-700 nm), but lower at short wavelengths (350-450 nm), than the light spectra in the habitats of P. h.chii. CONCLUSIONS: Two phylogenetically closely related bitterlings, P. h. himantegus and P. h. chii, dwell in different waters and exhibit different nuptial colorations and spectral sensitivities, which may be the results of speciation by sensory drive. Sensory ability and signal diversity accommodating photic environment may promote diversity of bitterling fishes. UV light was demonstrated to be a possible component of bitterling visual communication. The UV cue may assist bitterlings in genderidentification.

Androgens increase lws opsin expression and red sensitivity in male three-spined sticklebacks.

Optomotor studies have shown that three-spined sticklebacks (Gasterosteus aculeatus) are more sensitive to red during summer than winter, which may be related to the need to detect the red breeding colour of males. This study aimed to determine whether this change of red light sensitivity is specifically related to reproductive physiology. The mRNA levels of opsin genes were examined in the retinae of sexually mature and immature fish, as well as in sham-operated males, castrated control males, or castrated males implanted with androgen 11-ketoandrostenedione (11 KA), maintained under stimulatory (L16:D8) or inhibitory (L8:D16) photoperiods. In both sexes, red-sensitive opsin gene (lws) mRNA levels were higher in sexually mature than in immature fish. Under L16:D8, lws mRNA levels were higher in intact than in castrated males, and were up-regulated by 11 KA treatment in castrated males. Moreover, electroretinogram data confirmed that sexual maturation resulted in higher relative red spectral sensitivity. Mature males under L16:D8 were more sensitive to red light than males under L8:D16. Red light sensitivity under L16:D8 was diminished by castration, but increased by 11 KA treatment. Thus, in sexually mature male sticklebacks, androgen is a key factor in enhancing sensitivity to red light via regulation of opsin gene expression. This is the first study to demonstrate that sex hormones can regulate spectral vision sensitivity.

Response properties of crayfish antennules to hydrodynamic stimuli: functional differences in the lateral and medial flagella.

Antennules have been reported to influence localization of distant food odors, sex discrimination, and agonistic and social behaviors of decapod crustaceans. Although olfaction by the antennules is largely recognized, information on the sensitivity of antennules to hydrodynamic stimuli has been scant. In red swamp crayfish Procambarus clarkii antennules, mechanosensory setae outnumber the chemosensory setae. We studied the mechanosensitivity of crayfish antennules by recording neural activities from isolated antennules in response to sinusoidal dipole stimuli. Both the lateral and the medial flagellum of the antennules responded to hydrodynamic stimuli, although the medial flagellum showed more sensitivity at frequencies higher than 60 Hz. The most dominant setae present on the stimulated site were the simple setal type. Although both lateral and medial flagella are capable of detecting chemical and hydrodynamic cues, results from neural responses, morphological observations and antennular behavior observations indicate that the lateral flagellum of P. clarkii functions as an olfactory organ whereas the medial flagellum complements as a hydrodynamic receptor. It appears that in crayfish antennular sensory processing, crayfish simultaneously use chemical and hydrodynamic information. We have compared our data with the threshold of fish lateral line to the same stimuli and we discuss probable similarities in response properties.