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 of Pacific Saury <Emphasis Type="Italic">Cololabis saira</Emphasis> for understanding capture process

ABSTRACT:   To understand the mechanism of the behavioral response in the capture process of how fish recognize fishing gear and then how they can avoid the gear, the visual acuity of Pacific saury Cololabis saira was investigated by histological examination of the retina of individuals in the size range of 75–365 mm fork length (FL). The contour map of cone density distribution shows that the highest cone density is located in the temporal area of the retina, which indicated the visual axis as the forward direction. The visual acuity (VA) depends both on the focal length of the lens and the number of cones in the retina. The lens diameter increased linearly from 1.40 to 4.73 mm with fish growth, while the cone density decreased gradually from 765 to 378 cells/0.01 mm². Our results show that the visual acuity increases proportionately from 0.057 to 0.140 for individuals ranging in FL from 75 to 365 mm as expressed by the equation VA  = 0.0065 ×  FL ^0.5271 ( r ² = 0.9624).     

Putative ultraviolet-photosensitivity in the retina of 1-year-old nibbler <Emphasis Type="Italic">Girella punctata</Emphasis>: Based on molecular and histological evidences

ABSTRACT:   Ultraviolet (UV) photosensitivity in 1-year-old nibbler Girella punctata , which inhabits the coastal reefs of Japan, was investigated, based on retinal histology and visual pigment cDNA cloning. The retinal cone mosaic of the nibbler showed a square-shaped arrangement of double cones with a central single cone and accessory corner cones, which are representative putative UV-photoreceptors, at each corner of the square. Six cDNA fragments encoding putative visual pigment of nibbler were isolated and sequenced. Its deduced amino acid sequences were classified into five classes of opsin: UV, blue, green (one gene each), red (two genes), and rod (one gene) by comparison with other teleost opsins and phylogenetic analysis. Possible contributions of UV-sensitivity in nibbler was discussed regarding homing, feeding, and schooling.     

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.     

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.     

Annual occupation pattern of temperate rocky reefs by the Argentine sandperch Pseudopercis semifasciata in San José Gulf Marine Park, Argentina

Abstract  The Argentine sandperch, Pseudopercis semifasciata (Cuvier), is the target of unregulated recreational and artisanal fisheries within the northern Patagonian gulfs of Argentina. Being a reef species, the applicability of conventional large-scale assessment and management approaches appear limited. A more suitable alternative might be offered by spatial approaches, but their effectiveness would depend on the species' degree of mobility. Underwater visual censuses were used to study the annual occupation pattern of shallow rocky reefs by P. semifasciata to evaluate the possible occurrence of spawning migrations and the potential of reserves to protect the stocks. The abundance of P. semifasciata was greatest in winter, intermediate in autumn and lowest in spring and summer, but densities were relatively stable and oscillated ±17–31% around the overall mean for each reef. There was no evidence of spawning migrations as no demographic changes were observed throughout the year. Young sandperches (<1 year old) were never observed on the reefs. Implications of the results for the management of this species are discussed.     

Modelling the influence of light, turbulence and ontogeny on ingestion rates in larval cod and herring

Based on existing models of fish vision and turbulence-mediated ingestion rates, we develop a model of ingestion rates in larval fish that combines several physical properties of the environment (turbulence, irradiance, light attenuation) and visual characteristics of predators and prey. The model of visual range was calibrated with observed estimates in larval herring ( Clupea harengus ) and cod ( Gadus morhua ). The improved visual ability with length of larvae was predicted to be the most sensitive part of the model. Both turbulence and light had strong impacts on the ingestion rate of larval fish. The optimal level of turbulence increased with larval length. Also, due to the exponential decay of light with depth, it was predicted that larvae will have higher ingestion rates near the surface, even at high wind velocities. It is also proposed that larvae (particularly the smallest larvae) should concentrate on larger prey in turbulent environments. We suggest that biophysical models of larval growth and survival in field situations should include these factors to account for environmental effects on growth, survival and recruitment processes in the early life stages.     

Predation risk allocation or direct vigilance response in the predator interaction between perch (Perca fluviatilis L.) and pike (Esox lucius L.)?

Abstract –  Predation risk allocation hypothesis predicts that a prey's response to predator depends on prey's previous experience on predator. Here we tested whether the group of three perch respond differentially to pike, predator of perch, depending on the timing of high constant (HC) and high unpredictable (HU) risk periods within low constant risk periods in short-term (10 h) experiments, and whether the response is stronger during a HU risk period than during a HC risk period. Perch clearly erected the dorsal fin in response to predation risk treatments (pike odour only, odour and visible pike). Decrease in activity and increase in shoaling behaviour were observed mainly during high risk periods. However, the perch's responses to pike did not differ statistically between periods of various levels of predation risk or depending on the timing of high risk situations within constant low risk periods, and thus, suggesting that perch respond mainly to changes in the current predation risk.     

Red operculum spots,body size,maturation and evidence for a satellite male phenotype in non‐native European populations of pumpkinseed Lepomis gibbosus

Carotenoid‐based pigmentation is a striking feature of many taxa, yet the function, if any, of colour traits is often unclear. Pumpkinseed Lepomis gibbosus, a widely introduced freshwater sunfish that exhibits alternative male mating strategies, express a striking, red operculum spot. To investigate the potential function of this red spot as a signal in this species' mating system, we determined the presence and measured the size of red operculum spots in fish collected from 12 populations in five European countries in which pumpkinseed is an established non‐native species. We subsequently related the presence and size of the red spot to body size and mating strategy, based on an analysis of relative gonad size (gonado‐somatic index, GSI), using a mixed modelling approach. The study demonstrated that the presence of a red operculum spot in pumpkinseed is associated with sexual maturation, with GSI frequency distributions suggesting that cuckolders in some non‐native populations comprised both sneaker and satellite males, the latter not having previously been reported for this species. Further, the size of red spot correlated strongly with body size in parental and cuckolder males, although there was no difference in the presence or size of the red operculum spot between male mating strategies. The function of a red operculum spot in females is not clear but may be partly mediated by pleiotropic genetic mechanisms. Red operculum spots appear to function as signals of male maturation and body size in pumpkinseed, irrespective of mating strategy.     

A conservation trade‐off? Interspecific differences in seahorse responses to experimental changes in fishing effort

• 1. A 2‐year experimental seining programme and underwater visual censuses were undertaken to quantify the direct effects of active demersal fishing on the population structure and relative abundance of two sympatric seahorse species of conservation concern: the European long‐snouted seahorse, Hippocampus guttulatus Cuvier 1829 and the short‐snouted seahorse, Hippocampus hippocampus L. The influence of habitat preference on population‐level responses to changes in habitat structure following a reduction in fishing effort was also investigated.
• 2. It was predicted that the benthic habitat would be more structurally complex after fishing ceased and that seahorse densities would increase in response to reduced fishing mortality. Furthermore, it was predicted that the magnitude of the increase in density would be greater for H. guttulatus than for H. hippocampus, because the former species prefers complex vegetated habitats while the latter species uses sparsely vegetated habitats.
• 3. As predicted, the amount of habitat cover increased significantly when seining ceased, primarily through increases in the abundance of drifting macroalgae and unattached invertebrates. Despite similarities in life histories, the two seahorse species responded differently in terms of magnitude and direction to reduced fishing effort: the abundance of H. guttulatus increased significantly while H. hippocampus decreased in abundance.
• 4. Results suggest that active demersal fishing may influence the magnitude and direction of the responses of benthic marine fishes to exploitation through its impacts on habitat structure. An increase in habitat cover appeared to favour higher densities of H. guttulatus when seining effort was reduced. By contrast, repeated seining, which maintained less complex habitats, appeared to favour greater abundances of H. hippocampus.
• 5. Given differences in habitat preference among benthic marine fishes subject to incidental capture in fisheries, simultaneous attempts to manage populations of sympatric species may require complementary strategies that support the persistence of diverse habitat types.

Copyright © 2006 John Wiley & Sons, Ltd.     

Enhanced expression of stress protein 70 in the brains of goldfish, Carassius auratus, reared with bluegills, Lepomis macrochirus

Induction of stress protein (HSP70) was studied in goldfish (Carassius auratus) reared with bluegills (Lepomis macrochirus), a predator of small fish. HSP70 was identified by Western blotting and quantified by optical density after SDS-PAGE. The expression of HSP70 was significantly enhanced in the brains of goldfish reared with bluegills for 6 and 12 h in a single tank. The hepatopancreas and the kidney were not affected by the treatment. When goldfish were separated from bluegills with a partition net (1×1 cm mesh size), this protein also increased in the brains after 6 h but then returned to the control level after 12 h. When the goldfish and bluegills were kept in separate tanks and were not able to see each other but were connected by circulating water, HSP70 levels in the goldfish were unaffected. Immunohistochemical observations indicated that an anti-HSP70 antibody was found to react predominantly with the optic and vagal lobes of the brains. These results suggest that visual perception plays a primary role in enhancement of HSP70 expression in the goldfish reared with bluegills.     

Impacts of longfin eels (Anguilla dieffenbachii) on the behaviour of common bullies (Gobiomorphus cotidianus) held in captivity

Abstract – Interactions between common bullies (Gobiomorphus cotidianus) and longfin eels (Anguilla dieffenbachii) were studied in aquaria where bullies were subject to one of four treatments – bullies alone (allopatry), bullies and an eel (sympatry), or bullies provided with either visual cues (eel in adjacent compartment of the aquarium) or odour cues (eel in separate upstream aquarium). The total time that bullies were active (movement) and their use of rocks were recorded continuously over 48 h with a video camera. Analysis showed that for movement, there were no significant differences between treatments, but there were diel differences within sympatric treatments with greater activity evident during the night than during the day. In contrast, the use of rocks showed significant differences both between and within treatments; again, the only significant diel difference was in sympatry. Post hoc tests between treatments revealed that there were no differences at night, but during the day, there were differences between allopatry and visual trials, sympatry and visual trials, and sympatry and odour trials. No predation or other aggressive behaviour by eels towards bullies was observed in any trial. It was concluded that the presence of eels affected both bully activity and use of rocks, but this response was not solely due to either visual or odour cues. Changes in movement and the use of rocks appear to require multiple cues, and denial of either visual or odour cues was insufficient to elicit a response.     

Experimentally increased turbidity causes behavioural shifts in Lake Malawi cichlids

Abstract – The aquatic environment is being perturbed globally through increases in turbidity, which can have detrimental effects for the maintenance of fish diversity, especially in species dependent on visual cues for reproduction and species recognition. We performed a short‐term manipulation of the visual environment in Lake Malawi to test for an immediate behavioural response to increased turbidity in territorial rock‐dwelling cichlid fishes that use colourful visual cues to maintain territories near the substrate and attract mates. We found a significant movement of fish away from the substrate, with a concomitant shift from displaying territorial and courting behaviours to foraging behaviours, during the five minutes following the release of a turbidity plume over the area. This study is the first to test for and demonstrate an immediate behavioural response of a natural fish population to a short‐term increase in turbidity that might mimic the initial (i.e., immediate) stage of a run‐off event after rainfall in a deforested area.     

1999-2019年国内浮游动物研究进展、热点变化及展望

基于中国知网文献检索数据库 (CNKI),利用文献计量学中的可视化分析软件CiteSpace,对近二十年来国内核心期刊报道的浮游动物研究成果进行了分析和归纳总结。通过CiteSpace软件进行关键词突现分析,发现近二十年来国内浮游动物的研究主要集中在以下四个方面：1. 水产养殖;2. 环境监测与生态治理;3. 多样性及群落结构特征;4. 新技术在浮游动物研究中的应用。分析还发现国内浮游动物的研究热点正逐渐由水产养殖向生态环境方面转移。总体来看,国内有关浮游动物对全球气候变化的响应、生态系统修复及富营养化生物控制方面的研究不够深入,需要进一步加强。     

Changes in rhodopsin-porphyropsin ratio of chum and pink salmon

ABSTRACT:   In order to investigate the changes in rhodopsin-porphyropsin ratio of chum salmon and pink salmon in relation to the change in their habitat, the ratios were analyzed in individual fish prior to stocking, during the sea run, homing, and upstream migration. The ratio in both the species gradually increased during the sea run. However, the ratio decreased after upstream river migration. Moreover, in the sea, the rhodopsin-porphyropsin ratio of chum salmon was always slightly higher than that of pink salmon. The largest difference in the individual variation was observed in the individuals caught with a set net placed near the mouth of a home river.     

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.     

Carotenoids and retinal levels in captive and wild shrimp, Litopenaeus vannamei

In farm‐raised marine organisms, the interactions and functions of carotenoid and retinoid micronutrients as free radical scavengers during specific physiological processes, such as gonadic maturation, are not known. Captive and wild female white shrimp, Litopenaeus vannamei, were sampled at two maturation stages: II and IV. Total carotenoids, a carotenoid profile, and vitamin A from the digestive gland and ovary were determined. Superoxide dismutase (SOD) activity was determined in hemolymph. The carotenoid concentration and range of activity were significantly higher (P < 0.05) in wild than in captive shrimp, particularly at maturation stage IV. Activity of SOD in hemolymph of captive shrimp at both stages of maturation was significantly greater (P < 0.05) than that of wild organisms. In sexually exhausted, level IV captive shrimp, low carotenoid concentrations, mainly in digestive gland and ovary, reflected scavenger action insufficient to neutralize oxidative stress processes, as suggested by SOD activity. Carotenoids are important nutrients associated with the reproductive capacity of shrimp.