Comparison of visual acuity and visual axis of three flatfish species with different ecotypes

ABSTRACT:   The visual acuity, visual axis and visual accommodation of pointhead flounder, slime flounder, and red halibut were determined to obtain basic knowledge for developing appropriate fishing gear and fishing methods for sustainable fisheries. Each of these species has a different ecotype in terms of habitat, depth and prey species. Thus, it was hypothesized that they may differ in terms of visual acuity, visual axis and visual accommodation. Few studies have compared these characters in flatfishes from different ecotypes. We used histological methods to determine visual acuity (i.e. cone cell density) and visual axis (i.e. cone cell distribution) in each of these species. The maximum visual acuity was 0.127 in pointhead flounder (total length, TL 344 mm), 0.092 in slime flounder (TL 372 mm) and 0.109 in red halibut (TL 336 mm). Based on the cone cell distribution in the retina, the visual axis was upward and forward in pointhead flounder, forward and downward in slime flounder, and downward in red halibut. Finally, the mean angle of lens movement was −2° in pointhead flounder, −13° in slime flounder and −32° in red halibut. This measurement of lens movement indicated that the average near-point distance was 0.87 × TL in pointhead flounder, 0.65 × TL in slime flounder and 1.02 × TL in red halibut. At similar TL (336–355 mm), the visual acuity of these species differs depending on the direction in which they are looking.     

Color vision, accommodation and visual acuity in the largemouth bass

The largemouth bass is a sight feeder and one of the most popular freshwater fish for lure fishing. While lures a have variety of colors and forms, there is no information on the color vision and form perception in the largemouth bass. We recorded S-potentials from the isolate retinae of the largemouth bass to examine color vision electrophysiologically. The occurrence of the C-response provided direct evidence for the possession of color vision. L-responses recorded indicated a high spectral sensitivity to red. The direction and distance of lens movement of a specimen of 43 cm in fork length indicated a horizontal visual axis and the near point at 13.5 cm, respectively. The visual acuity calculated from the cone density and the focal distance of the lens was 0.10. Histological characteristics of the retina indicated that the eyes are well adapted to both form and movement perceptions.     

Comparison of the spectral sensitivity of juvenile red sea bream investigated by the physiological technique and by the behavioral technique

ABSTRACT:   The optomotor reaction of the red sea bream Pagrus major was utilized in order to measure its spectral sensitivity. The high spectral sensitivity of this species in twilight conditions was estimated to be from 480 to 560 nm, whereas it was observed to be also on longer wavelengths in the probable photopic vision. This result was compared with the sensitivity curve obtained by the physiological technique of the induction of electroretinogram. The form of both sensitivity curves did not show similar tendencies. It will be necessary to investigate the adjustment of a physiological phenomenon and a behavioral phenomenon concerned with various stimulus-reaction systems.     

Longer wavelengths of light improve the growth, intake and feed efficiency of individually reared juvenile pikeperch Sander lucioperca (L.)

We tested the effects of monochromatic light on the specific growth rate (SGR), feed intake and feed efficiency (FE) of juvenile pikeperch, Sander lucioperca (L.). Pikeperch were reared individually for 42 days in aquaria covered with blue, green, yellow or red gelatin filters or white paper (control; n =5). Linear regression analysis indicated a significant positive effect of longer wavelengths of light on the condition factor (CF), FE and SGR. The final weight, SGR and CF were significantly higher in fish reared under red than under white light, and FE was better under green, yellow and red light than under white light (Dunnett's post hoc test, P <0.05) while blue was comparable to white light in terms of the measured parameters. After the growth trial, the spectral sensitivity of photoreceptor cells in the retina was tested using microspectrophotometry, which revealed the presence of rods with λ_max at ca. 530 nm and two cone classes, absorbing maximally at ca. 535 and 603 nm, all containing a porphyropsin-based pigment. These results suggest that the presence of mid and long wavelength-sensitive cones enhances visual sensitivity under mid-wavelength and long-wavelength environments, and thus supports the finding that longer wavelengths of incoming light can improve FE and SGR of the cultivated pikeperch.     

Distribution patterns of five pleuronectid species on the continental slope off the Pacific coast of northern Honshu,Japan

Information on the distributions of demersal and benthic fishes is fundamental for stock assessment and management. Spatiotemporal changes in the distribution patterns of five pleuronectid species (flathead flounder Hippoglossoides dubius, Kamchatka flounder Atheresthes evermanni, roughscale sole Clidoderma asperrimum, slime flounder Microstomus achne, and Korean flounder Glyptocephalus stelleri) off the Pacific coast of northern Honshu, Japan, at depths of 150–900 m, were examined using a generalized linear mixed model (GLMM). Densities of flathead and Korean flounder were highest in the southernmost area, where the fish were small. The body lengths of both of these species increased from 2003 to 2008, suggesting that an abundant year class was recruited in 2003. The density of Kamchatka flounder was highest in the northern area. In roughscale sole and slime flounder, there were no distinctive annual and latitudinal trends in the density distributions. The density distribution of Korean flounder was bimodal; the peaks were at depths of 210 and 410 m. The body length increased as the depth increased from 150 to 410 m, and then decreased from 410 to 550 m. Moreover, “bigger–deeper” trends were observed in flathead, Kamchatka and slime flounder.     

Habitat utilization,feeding, and growth of wild spotted halibut <Emphasis Type="Italic">Verasper variegatus</Emphasis> in a shallow brackish lagoon: Matsukawa-ura,northeastern Japan

Habitat utilization, feeding, and growth of a rare pleuronectid flatfish, spotted halibut Verasper variegatus, were examined in a brackish lagoon in northeastern Japan: Matsukawa-ura. The distribution and date–length data of spotted halibut collected mainly from beam-trawl samplings during 1983–2008 indicated that age-0 juveniles [n = 25, 6.0–18.0 cm total length (TL)] and older spotted halibut (n = 71, 13.8–43.0 cm TL) inhabited almost the entire northern part of Matsukawa-ura. Comparative distribution surveys of spotted halibut, stone flounder, and marbled flounder during 1985–1989 revealed similar distribution patterns of these flatfishes; the highest densities were found around the central part of Matsukawa-ura, although significantly lower abundance was detected for spotted halibut. Linear growth equations of age-0 juveniles demonstrated that spotted halibut were able to achieve high growth after June, probably because abundant prey (e.g., mysids and gammarids) and suitable physical conditions (warmer water temperature and lower salinity) were present. The main prey items shifted from various crustaceans including mysids, caridean shrimps, and anomurans to brachyura Hemigrapsus spp. (≥20 cm TL). Our study shows that spotted halibut use the shallow brackish lagoon as an important nursery for juveniles, and also as a feeding ground for young and adults.     

Changes in the scotopic vision of juvenile Pacific bluefin tuna (Thunnus orientalis) with growth

In cultured juvenile Pacific bluefin tuna (Thunnus orientalis), reducing the mass deaths caused by collision or contact with tank or net walls at night is a priority for seedling production. Pacific bluefin tuna is a visually dependant species, although its scotopic vision is poor. We recorded electroretinograms to investigate the visual function with growth in the dark-adapted eyes of juvenile Pacific bluefin tuna. Peak wavelengths of spectral sensitivity [38–62 days posthatch (dph), 77–167 mm standard length (SL)] were observed between 474 and 494 nm. Visual light sensitivity has a tendency to increase slightly with growth at 28–64 dph in individuals that measured 29–175 mm SL. However, visual temporal resolution did not significantly increase with growth at 38–62 days dph in individuals that measured 77–167 mm SL. These results suggest that the mass death continues between 28 and 64 dph because of low visual function and increasing swimming speed with growth.     

Visual spectral sensitivity of photopic juvenile Pacific bluefin tuna (Thunnus orientalis)

Although Pacific bluefin tuna is a species that relies on vision, its photopic visual function is not well known; we therefore recorded electroretinograms to investigate photopic spectral sensitivity in juveniles of this species (49-81?days post-hatch; standard length 74-223?mm). The peak spectral sensitivity wavelength was 505?nm. We estimated that two (λ(max)?=?512-515?nm and 423-436?nm) or three (λ(max)?=?512-515?nm, 423-436?nm, and 473?nm) types of cone visual pigments contribute to photopic vision; these spectral sensitivities are adapted to surface water habitats in clear ocean and coastal water.     

Occurrence and distribution of settling and newly settled spotted halibut Verasper variegatus and Japanese flounder Paralichthys olivaceus in shallow nursery grounds around Shimabara Peninsula, western Japan

The occurrence and distribution of settling and settled spotted halibut Verasper variegatus were compared with those of Japanese flounder Paralichthys olivaceus in shallow habitats around Shimabara Peninsula, western Japan, to elucidate the settlement and recruitment characteristics of spotted halibut, a rare pleuronectid flatfish in Japan. Push-net sampling conducted at nine sites in March and April 2003 collected spotted halibut from four nurseries located at eastern areas of Shimabara Peninsula in Ariake Bay; Japanese flounder were sampled from eight nurseries. Comparison of microhabitat distributions in a tidal-flat nursery during February?CApril in 2003?C2007 revealed that metamorphosing larvae and juveniles of spotted halibut, which showed the drastic body coloration (black to brown) and behavioral changes (frequent swimming to settlement), were distributed mainly in the lower edge of the intertidal area, whereas Japanese flounder inhabited both intertidal and subtidal areas. Metamorphosing larvae of spotted halibut (12.6?C16.5?mm standard length; n?=?24) were collected in March when the highest densities were observed, whereas metamorphosing larvae of Japanese flounder (10.0?C15.9?mm, n?=?55) were observed during March?CApril. Our results suggest that spotted halibut has a narrower time/space window for recruitment to the specific nurseries compared with Japanese flounder.     

Genetic population evaluation of two closely related flatfish species, the rare barfin flounder and spotted halibut, along the Japanese coast

ABSTRACT:   Barfin flounder and spotted halibut have been selected as target species for stock enhancement in Japan. Understanding the genetic condition of the wild stock is a principal requirement in any stock enhancement program. The genetic variability of barfin flounder and spotted halibut, and the population structure of spotted halibut were evaluated using microsatellite DNA markers (msDNA) and the control region of the mitocondrial DNA (mtDNA). Barfin flounder and spotted halibut showed high genetic variability at the msDNA level. Barfin flounder A was 16.7 and H _e was 0.860; spotted halibut A _n ranged from 7.7 to 10.2 and H _e ranged from 0.710 to 0.774. At the mtDNA level, high haplotype ( h  = 0.922) and low nucleotide (π = 0.002) diversities were observed for barfin flounder; however, low haplotype and nucleotide diversities ( h  = 0.603–0.620 and π = 0.001–0.002), and very low haplotype and nucleotide diversities ( h  = 0.193 and π = 0.0003) were observed for spotted halibut in the north and south locations, respectively. Slight genetic differentiation among spotted halibut sampling locations was observed from the msDNA. MtDNA analyses showed genetic differentiation between north and south locations, but not within them. The designation of north-specific and south-specific management units in the future stock enhancement activities of spotted halibut is recommended.     

First description and collection records of juvenile slime flounder <Emphasis Type="Italic">Microstomus achne</Emphasis> from the eastern and western coastal waters off Honshu Island,Japan

Morphological characteristics and body pigmentations of juvenile slime flounder Microstomus achne were described from one specimen [27.8 mm total length (TL)] collected off Niigata Prefecture from the Sea of Japan (35 m depth) in May 1993 and from three specimens (30.1, 36.2, and 40.9 mm TL) collected off Fukushima Prefecture on the Pacific coast of northern Japan (15 and 50 m depths) during April–May 2008 and 2009. These age-0 juveniles had a characteristically slenderly oval-shaped body and slightly protruded front nostrils. Sparsely distributed melanophores and xanthophores were clearly visible throughout the ocular side of one specimen, which was judged as a newly settled juvenile, whereas several spots aggregated by small melanophores were found in the others with elongated pectoral fins and small cycloid scales. Melanophores were only slightly detectable on the blind side. Comparisons of the depth distributions of slime flounder juveniles and sympatrically collected age-0 pleuronectids (Pseudopleuronectes herzensteini, Pseudopleuronectes yokohamae, Platichthys bicoloratus, and Dexistes rikuzenius) suggested that slime flounder can settle on broad nursery areas of coastal and offshore pleuronectid flatfishes, probably depending on local oceanic conditions during the protracted pelagic phase.     

Color vision, spectral sensitivity, accommodation, and visual acuity in juvenile masu salmon Oncorhynchus masou masou

ABSTRACT:   Color vision, spectral sensitivity, accommodation, and visual acuity were examined in juvenile masu salmon Oncorhynchus masou masou to obtain fundamental information about the visual system. Two types of S-potentials were recorded from 415 horizontal cells in isolated retinas from 34 cultured freshwater masu salmon (114–219 mm standard length, SL). Although horizontal cells recording S-potentials were not identified, the horizontal cells were confirmed because their responses were maintained while the stimulus remained. The variety of chromaticity (C)-type S-potentials indicated well-developed color vision. The analysis of the luminosity (L)-type S-potentials indicated that the peak spectral sensitivity was at 522 nm. S-potentials were also recorded in response to ultraviolet light. The direction and extent of lens movement induced by electrical stimulation was measured in 12 cultured masu salmon (99.0–142.5 mm SL). The results indicated that the visual axis was upward and forward, and that the range of accommodation was from 0.79 × SL in front of the eye to infinity. In histological analysis of the retinas of five wild smolts (100–118 mm SL), the maximum cone densities (276–345 cones/0.01 mm²) were detected in the ventral to temporal regions. The visual acuities assessed by histological methods were 0.069–0.075.     

Comparing the roles of Pacific halibut and arrowtooth flounder within the Gulf of Alaska ecosystem and fishing economy

The fishing industry of the western and central regions of the coastal Gulf of Alaska (CGoA) directly employs over 17,000 people and processes fish with a wholesale value of US$618 million annually. Pacific halibut (Hippoglossus stenolepis) are a valued groundfish species because of the high quality of their flesh. In contrast, arrowtooth flounder (Atheresthes stomias) are much more abundant but of low value because their flesh degrades upon heating. Both are high trophic level predators but play different roles in the ecosystem because of differences in abundance and diet. Using an end‐to‐end ecosystem model, we evaluate the impact of alternate levels of fishing effort and large‐scale changes in oceanographic conditions upon both species, the ecosystem, and the fishing economy. Reduction of longline efforts to reduce Pacific halibut mortality led to reduction in total value of all CGoA landings but increase in value landed by sport fisheries, trawl fleets, and fish pot vessels as they exploit a greater share of available halibut, sablefish, and Pacific cod. Increased trawl effort to raise arrowtooth flounder mortality led to increase in total value of all landings but large reductions in value landed by longline, jig, fish pot, and sport fleets with greater competition for available Pacific cod, halibut, and sablefish. Oceanographic conditions that enhance pelagic food chains at the expense of benthic food chains negatively impact groundfish in general, though Pacific halibut and arrowtooth flounder are resilient to these effects because of the high importance of pelagic fish in their diets.     

容器颜色对漠斑牙鲆白化率和成活率的影响

本文就培养容器的颜色对漠斑牙鲆稚鱼的白化率和生长率的影响进行初步研究。结果表明:用深蓝色和黑色等深色容器培养的稚鱼白化率显著低于白色和黄色等浅色容器(p<0.05),黑色、深蓝色、黄色和白色4个组别(N=100)的白化率分别为20.8%、14.4%、57.6%和86.6%;白色最高为86.6%,深蓝色最低为14.4%;而用不同颜色的容器培养漠斑牙鲆的稚幼鱼,对其成活率影响不大(p>0.05),黑色、深蓝色、黄色和白色4个组别的成活率分别为96.0%、90.0%、82.5%、93.0%;白化稚幼鱼的生长发育并无异常。     

Visual acuity and spectral sensitivity of the elkhorn sculpin <Emphasis Type="Italic">Alcichthys alcicornis</Emphasis>

ABSTRACT:   In this study, the visual acuity, visual accommodation, and spectral sensitivity of the elkhorn sculpin were determined. The elkhorn sculpin Alcichthys alcicornis is a typical groundfish that has conspicuously large eyes. They are caught by bottom gillnets, trawl nets, bottom line angling, and other fishing methods. Although fish behavior arising from visual stimuli is important in these fishing methods, there is little information available regarding the visual sensitivity of the elkhorn sculpin . Three specimens, with total lengths of 300–310 mm, were studied. Visual acuity was calculated, from the maximum cone density in the retina, to be between 0.10 and 0.14. The minimum separable angles were calculated to be 7.14–10.37 min. Measurement of lens movement in five specimens indicated that the near-point distance was between 0.87 and 1.53 times the total length. Lens direction was estimated to be 11–22° in the downward visual axis. Spectral sensitivity was also determined electrophysiologically by recording S-potentials. Three types of response were obtained from 21 specimens, including L responses that showed hyperpolarization at all wavelengths of stimulating light, and two C responses that showed wavelength-dependent hyperpolarization and depolarization. Based on these results, the elkhorn sculpin has color vision and its sensitivity is most acute in light with a wavelength of 554 nm.     

Visual acuity and spectral sensitivity of Jacopever Sebastes schlegeli

Understanding the behavior of Jacopever Sebastes schlegeli to visual stimulation is important and requires determination of visual sensitivity through the use of effective stimulation. In the present study, we measured the visual acuity, visual accommodation and spectral sensitivity of Jacopever. Visual acuity was calculated from the maximum cone density in the retina. In five specimens, the total length ranged from 17.6 to 24.5 cm and the calculated minimum resolving angles and visual acuities were 9.5–10.7 min and 0.09–0.11, respectively. Measurement of lens movement for visual accommodation indicated a mean distance and direction of movement of 0.31 mm and 16.0° in an upward and forward direction, respectively. The direction of accommodation and visual axis measured from the retinal area of maximum cone density were almost identical. The calculated focal distance was 0.74-fold the total length in the nearest point to infinity. We also determined the spectral sensitivity electrophysiologically by recording S-potentials from 45 specimens of total length of 15.4–47.5 cm. The S-potentials were recorded from 300 horizontal cells in the retina. All responses showed a similar spectral pattern, consisting of hyperpolarization in response to various wavelengths of stimulating light; the maximum amplitude of the response was recorded at 522 nm.     

The effect of light on activity and growth of Atlantic halibut, Hippoglossus hippoglossus L., yolk-sac larvae

The growth and activity of Atlantic halibut, Hippoglossus hippoglossus L., yolk-sac larvae exposed to light of differing intensities and wavelengths were investigated every fifth day. The experiments were conducted at 6 ^oC from day 1 until day 34 post hatch. Four intensities of constant white light (2.0, 0.3, 0.03 and 0.005 μ Em^?2 s^?1, λ_max 590 nm), and constant coloured light of equal intensities (0.03μ Em^?2s^?1) in the blue, green and red spectrums (λ_max 450, 560 and 670 nm, respectively) were used. In addition to a control treatment in constant darkness, one treatment was incubated in a 12:12 h light: dark photoperiod. The light treatments did not have any discernible effect on the total length, myotome height, dry weights or yolk conversion efficiencies. The most intense white light resulted in an increased activity on days 24 and 30 post hatch, resulting in a temporarily reduced length and myotome height for the larvae in these groups compared to the other treatments. Larvae from all treatments were of the same size 34 days post hatch. The dry weights of the larvae and yolk-sacs were unaffected by light treatment. The activity increased independently of light treatment until 120 degree-days, and thereafter, the strongest white light resulted in an temporarily increased activity. The distribution of activity changed independently of light regime in the beakers during development.     

Dim-light photoreceptor of chub mackerel <Emphasis Type="Italic">Scomber japonicus</Emphasis> and the photoresponse upon illumination with LEDs of different wavelengths

To study the absorption characteristics of rhodopsin, a dim-light photoreceptor, in chub mackerel (Scomber japonicus) and the relationship between light wavelengths on the photoresponse, the rod opsin gene was cloned into an expression vector, pMT4. Recombinant opsin was transiently expressed in COS-1 cells and reconstituted with 11-cis-retinal. Cells containing the regenerated rhodopsin were solubilized and subjected to UV/Vis spectroscopic analysis in the dark and upon illumination. Difference spectra from the lysates indicated an absorption maximum of mackerel rhodopsin around 500 nm. Four types of light-emitting diode (LED) modules with different wavelengths (red, peak 627 nm; cyan, 505 nm; blue, 442 nm; white, 447 + 560 nm) were constructed to examine their effects on the photoresponse in chub mackerel. Behavioral responses of the mackerels, including speed and frequencies acclimated in the dark and upon LED illumination, were analyzed using an underwater acoustic camera. Compared to an average speed of 22.25 ± 1.57 cm/s of mackerel movement in the dark, speed increased to 22.97 ± 0.29, 24.66 ± 1.06, 26.28 ± 2.28, and 25.19 ± 1.91 cm/s upon exposure to red, blue, cyan, and white LEDs, respectively. There were increases of 103.48 ± 1.58, 109.37 ± 5.29, 118.48 ± 10.82, and 109.43 ± 3.92 %, respectively, in the relative speed of the fishes upon illumination with red, blue, cyan, and white LEDs compared with that in the dark (set at 100 %). Similar rate of wavelength-dependent responses was observed in a frequency analysis. These results indicate that an LED emitting a peak wavelength close to an absorption maximum of rhodopsin is more effective at eliciting a response to light.     

Oocyte maturation and ovulation in the Atlantic halibut, Hippoglossus hippoglossus (L.), examined using ultrasonography

High resolution ultrasound scanning was tested as a non-invasive technique for monitoring oocyte maturation and ovulalion in the Atlantic halibut Hippoglossus hippoglossus (L.). Female broodstock halibut were examined using a 7.5-Mhz linear ultrasound transducer, prior to and during spawning. Representative images of halibut ovaries are presented and discussed. Individual oocytes of spawning females were discernible during oocyte final maturation, due to the large increase in volume caused by water uptake. The yolky (vitellogenic) cocytes of pre-spawning fish were more reflective to ultrasound than hydrating oocytes. The resulting differences in depth of ultrasound penetration permitted easy distinction of pre-spawning from spawning females. In addition, short-term changes in the depth of ultrasound penetration were observed during repeated scanning of a spawning female, owing to progressive hydration of the oocyte batch destined for ovulation. Although of similar diameter, hydrating oocytes in the ovarian tissue could be discerned from eggs in the ovarian lumen because of the different acoustic properties of the surrounding media. The findings of the present study are considered promising for the future routine use of ultrasonography in halibut broodstock management.     

光唇鱼对单色光偏好的性别差异及相关生理机制

为探究溪流性鱼类光唇鱼(Acrossocheilus fasciatus)对光色的偏好是否存在性别差异, 以及芳香化酶作为催化睾酮(T)向雌二醇(estradiol, E2)转化的限速酶在行为调节中的关键角色, 本研究采用行为学方法研究了雌鱼和雄鱼对 6 种单色 LED 光源的选择偏好, 并尝试利用药物抑制体内芳香化酶活力从而改变血浆性激素水平和鱼的行为表现。结果表明, 雌鱼和雄鱼分别相对偏好红光(峰值为 637 nm)和黄光(590 nm), 两者均相对排斥蓝光(465 nm)、 紫光(405 nm)以及含有蓝光波段的白光(447 nm), 而对绿光(518 nm)的偏好不明显。摄食含有芳香化酶抑制剂来曲唑(letrozole, LZ)的实验饲料 10 d 后, 雌性和雄性光唇鱼脑和性腺组织内芳香化酶活力和血浆 E2 水平均显著下降, 但血浆 T 水平无显著变化。值得注意的是, LZ 也导致处理鱼对光色选择偏好的改变, 雌鱼转为相对偏好蓝光, 雄鱼转为相对偏好红光。然而, 摄入含 LZ+E2 实验饲料后除芳香化酶活力降低外, T、E2 两种性激素水平和光色偏好行为表现均未出现明显变化。因此推测光唇鱼对光色偏好的性别差异极可能与体内芳香化酶活力和雌二醇水平的性别差异有关, 而与睾酮水平无明显关联。