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).     

Retinal ganglion cell topography in juvenile Pacific bluefin tuna Thunnus orientalis (Temminck and Schlegel)

The retinal ganglion cell distribution, which is known to reflect fish feeding behavior, was investigated in juvenile Pacific bluefin tuna Thunnus orientalis. During the course of examination, regularly arrayed cells with a distinctive larger soma, which may be regarded as motion-sensitive cells, were found. The topographical distribution of ordinary-sized ganglion cells, which is usually utilized to estimate fish visual axis and/or visual field characteristics, showed that the highest-density area, termed the area centralis, was localized in the ventral-temporal retina. The retinal topography of ordinary-sized ganglion cells seems to reflect the bluefin tuna’s foraging behavior; while cruising, cells in the area centralis may signal potential prey, such as small schooling pelagic fishes or squids, that are present in the upward-forward direction. Judging from morphological characteristics, the large ganglion cells localized in the small temporal retinal area seem to be equivalent to physiologically categorized off-center Y-cells of cat, which are stimulated by a transient dark spot in a bright visual field. It was inferred that presumed large off-center cells in the temporal retina detect movements of agile prey animals escaping from bluefin tuna as a silhouette against environmental light.     

Possibility for decreasing of mercury content in bluefin tuna <Emphasis Type="Italic">Thunnus orientalis</Emphasis> by fish culture

ABSTRACT:   The bluefin tuna tested were reared for 22 months from eggs before the beginning of the experiment, and sampling was performed every 3 months over the following year. The experimental results showed that the mercury concentration in the muscle ranged from 0.32 to 0.85 μg/g, which is lower than that found in wild bluefin tuna of a similar size. Increase in the mercury concentration corresponding to the increase in body weight was not shown, and it was quite different with wild bluefin tuna. Furthermore, no significant relationship was found between the lipid concentration and the mercury concentration in muscle. Among the internal organs of cultured bluefin tuna, the heart (0.32–0.66 μg/g), liver (0.43–0.99 μg/g) and spleen (0.59–1.0 μg/g) contained higher concentrations of mercury. It was estimated that the full-cycle cultured bluefin tuna had been fed small fish containing lower concentrations of mercury, and that the mercury concentration of tuna would be almost equal throughout the year because the effect of mercury accumulation would be weakened by body growth. Therefore, it was concluded that selecting diet fish species might decrease mercury contents in cultured bluefin tuna.     

Development of visual cells in the Pacific bluefin tuna <Emphasis Type="Italic">Thunnus orientalis</Emphasis>

The development of rod and cone photoreceptor cells was investigated in the retinas of Pacific bluefin tuna larvae and juveniles, using RET-P1 monoclonal antibody labeling to identify photoreceptors. At 60 h after hatching, which was about when feeding began, opsin (presumably green opsin (Rh2)) was expressed in the outer segments of cone cells. At 15 days after hatching (dah), although many labeled cone cells were observed in the dorsal retina, the same type of cone cells had partially appeared in the ventral retina. The presence of rod cell bodies was confirmed by the expression of Rh1 opsin at 15 dah. At 21 dah, the presence of outer segments of rod cells was confirmed by the expression of Rh1 opsin and by morphology. The observations suggest that the cone cells were substantially operable upon the development of their outer segment at around the beginning of the post-larval stage, and the rod cells began to function at around 15 to 21 dah, before and during metamorphosis.     

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.     

Changes of proximate compositions and myoglobin content in the dorsal ordinary muscles of the cultured Pacific bluefin tuna <Emphasis Type="Italic">Thunnus orientalis</Emphasis> with growth

ABSTRACT:   Using the dorsal ordinary muscle (DOM) of cultured Pacific bluefin tuna (body length [BL]: 47.5–81.8 cm, body weight [BW]: 2.1–13.5 kg, n  = 15), the changes of proximate compositions and myoglobin (Mb) content with growth were investigated. There was a positive correlation ( r  = 0.9832, P  < 0.05) of BL and BW in cultured tuna. The protein contents of the DOM of cultured tuna decreased ( P  < 0.05) and the lipid contents had a tendency to increase (not significantly) with growth. The meat color changed from pink to red with growth. In addition, the Mb contents of the DOM of cultured tuna increased ( P  < 0.05) from 1.0 mg/g (minimum BW fish) to 3.8 mg/g (maximum BW fish) with growth. These results indicate that the increase of the Mb content in the DOM of cultured tuna is not caused by the restriction of exercise and overfeeding between 2.1 kg and 13.5 kg of BW.     

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.     

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.     

Turbulence effect on survival and feeding of pacific bluefin tuna <Emphasis Type="Italic">Thunnus orientalis</Emphasis> larvae,on the basis of a rearing experiment

ABSTRACT:   Physical conditions such as oceanic turbulence related to food availability are considered to be important factors affecting fish larval survival. Rearing experiments were conducted to elucidate the effects of turbulence on the survival and feeding rates during the initial feeding period of Pacific bluefin tuna Thunnus orientalis . Six levels of turbulence intensity were provided by changing flow rates from pipes set on the bottom of rearing tanks. The result showed a dome-shaped relationship between turbulence level and survival rate, in which the feeding rate appeared higher at a logged turbulence energy dissipation rate of −6.32, and decreased at both higher and lower turbulence levels. Compared with the turbulence intensity in the ocean, the optimal turbulence level for Pacific bluefin tuna larvae corresponded to the turbulence caused by sea surface winds with speeds of 4–12.5 m/s. The estimated optimal turbulence intensity for Pacific bluefin tuna larvae is comparable to that for yellowfin tuna Thunnus albacares .     

Variability of preferred environmental conditions for Atlantic bluefin tuna (Thunnus thynnus) larvae in the Gulf of Mexico during 1993–2011

The Gulf of Mexico (GOM) is the primary spawning ground for western Atlantic bluefin tuna (Thunnus thynnus). In this work, information reported by previous studies about the preferred environmental conditions for the occurrence of bluefin tuna larvae in the GOM is integrated into a dimensionless index, the BFT_Index. This index is used to evaluate the spatial and temporal variability of areas with favorable environmental conditions for larvae within the GOM during 1993–2011. The main findings of this work are that: (i) the proposed index successfully captures the spatial and temporal variability in the in situ occurrence of bluefin tuna larvae; (ii) areas with favorable environmental conditions for larvae in the GOM exhibit year‐to‐year spatial and temporal variability linked with mesoscale ocean features and sea surface temperature; and (iii) comparison of the BFT_Index‐derived variability with recruitment of age‐0 fish estimated from recent stock assessment indicates that changes in environmental conditions may drive a relevant component (~58%) of the recruitment variability. The comparison with the recruitment dataset further revealed the existence of key regions linked with recruitment in the central/northern GOM, and that the Loop Current may function as a trap for larvae, possibly leading to low survival rates. Above (below) average conditions for occurrence of larvae in the GOM during spring were observed in 2000, 2001, 2002, 2006–2008, and 2011 (1994, 1996, 1998, 1999, 2003 and 2010). Results reported here have potential applications to assessment of bluefin tuna.     

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.     

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.     

Dietary utility of enzyme-treated fish meal for juvenile Pacific bluefin tuna <Emphasis Type="Italic">Thunnus orientalis</Emphasis>

ABSTRACT:   In order to develop an artificial diet, the dietary utility of enzyme-treated fish meal was investigated for juvenile Pacific bluefin tuna Thunnus orientalis (PBT). Diets containing each 63% of Chilean fish meal (FM), enzyme-treated Chilean fish meal (EC) and enzyme-treated Peruvian fish meal (EP), with 10% bonito oil and raw sand lance Ammodytes personatus (SL) were fed to juvenile tuna six times per day for one week. In a different trial, diets EC and SL were fed to tuna six times per day for 2 weeks. Only diet EC sustained similar growth or caused lower survival and higher feed efficiency, hepato- and enterosomatic indices and final carcass lipid content as compared to those of SL. Diets FM and EP led to lower specific growth rate (SGR) but similar feed efficiency, survival and hepatosomatic index, yet higher enterosomatic index. Moreover, PBT fed diet EC for 2 weeks led to similar growth performance but higher final carcass and hepatic lipid contents, and plasma cholesterol and phospholipid levels than those fed SL. Carcass fatty acid composition of diet EC group had lower 20:5  n -3 and 22:6  n -3 levels than the SL group. These results revealed that EC, as a suitable dietary protein source, could sustain growth of PBT, while dietary bonito oil led to higher carcass lipid but lower accumulation of n -3 highly unsaturated fatty acids.     

Retinomotor responses of juvenile bluefin tuna Thunnus thynnus

SUMMARY: In bluefin tuna culture, a high mortality of juveniles is caused by bumping into the tank and net-pen walls at dawn. This bumping can possibly be attributed to visually disoriented behavior of the fish. To examine this possibility, the authors carried out retinomotor response experiments with juvenile bluefin tuna (50.7–96.8 mm total length, at which they were transferred from a indoor tank to a sea net-pen) and measured ambient light intensity at the culture site at dawn. The light intensity at which the transition from scotopic to photopic vision takes place was 7.52 lx and the time taken by the transition was 15 min. At dawn, the ambient light intensity rapidly increased from scotopic light intensity level and attained photopic light intensity level in 10 min. This incompatibility of the retinal adaptation with the change in the ambient light intensity could cause the visual disorientation of the fish. It is therefore possible that the visually disoriented juveniles cannot control their high power swimming and thus bump into the walls at dawn.     

Sizes of adult bluefin tuna Thunnus orientalis in different areas of the western Pacific Ocean

ABSTRACT:   The length frequencies of adult Pacific bluefin tuna Thunnus orientalis caught near Japan, near Taiwan, in the tropical western Pacific Ocean, and in the South Pacific Ocean, were compared. The largest catches consisted of medium-sized adults (160–209 cm fork length) taken near Japan and large adults (≥210 cm) taken near Taiwan. Small adults (120–159 cm) were occasionally caught in the Sea of Japan. Small numbers of medium-sized and large adults were caught in the tropical western Pacific and the South Pacific. The length frequencies of the fish greater than 160 cm in length caught in different areas around Japan were similar to each other. As adult bluefin tuna grow older they spawn earlier, and their distribution, movements, and spawning areas change.     

Ontogenetic changes in RNA,DNA and protein contents of laboratory-reared Pacific bluefin tuna <Emphasis Type="Italic">Thunnus orientalis</Emphasis>

ABSTRACT:     The ontogenetic changes in the growth potential of larval and juvenile laboratory-reared Pacific bluefin tuna were examined based on RNA–DNA and protein–DNA ratios. Experimental fish were reared at the Ohshima Experiment Station of Kinki University Fisheries Laboratory in August 2002. Samples were taken from 13 to 35 days after hatching (DAH). Metamorphosis from larva to the juvenile stage was observed around 23 DAH. Somatic growth of Pacific bluefin tuna was accelerated after metamorphosis. The value of the RNA–DNA ratio from 13 to 19 DAH increased slightly from 3.77 ± 0.58 (mean ± SD) to 7.28 ± 2.23. After that, the ratio markedly increased from 13.89 ± 3.71 on 21 DAH to 19.11 ± 4.27 on 23 DAH, which was the end of the metamorphic period. After 25 DAH, the ratio remained at a high level of 15–20. The protein–DNA ratio showed a similar tendency to the RNA–DNA ratio. These results suggest that the rapid increase in the RNA–DNA ratio in the metamorphic period supports the consequent rapid somatic growth in the juvenile stage. The high ratio after the metamorphic period could be because of the species-specific traits large prey exhibit for their survival and because of the tuna's fast -growth after the juvenile stage.     

Inclusion of prey data improves prediction of bluefin tuna (Thunnus thynnus) distribution

We examined the distribution of Atlantic bluefin tuna ( Thunnus thynnus ) in the Gulf of Maine, Northwest Atlantic Ocean, from 17 to 23 August 1995, in relation to physical and biological parameters. Specifically, we fit a binomial GLM to the bluefin tuna presence–absence data and predictor variables that include: sea surface temperature (SST), ocean depth, distance to an SST front, time-lagged density of SST fronts, and an interpolated surface of Atlantic herring ( Clupea harengus ) density. In addition, we use simple and partial Mantel tests to examine whether bluefin tuna presence–absence data are significantly associated with these predictors, once spatial autocorrelation is accounted for. Results suggest that the distribution of bluefin tuna significantly correlated with herring density ( z  =   3.525, P  =   0.000424), and that inclusion of biological variables results in a more parsimonious model. Mantel tests results indicate that bluefin tuna abundance is significantly correlated with herring density after the effect of spatial structure is removed (Mantel r  =   0.043, P  <   0.019).     

Recruitment abundance index of Pacific bluefin tuna using fisheries data on juveniles

ABSTRACT:   The recruitment abundance index of Pacific bluefin tuna Thunnus orientalis was estimated from 1980 to 2003 fishing year by using the troll fishery data in Nagasaki Prefecture, western Japan. It has been shown that the troll fishery in Nagasaki Prefecture operates with good time–area coverage of the species habitat, and that the fishing power slightly changed during the period analyzed, based on fisheries statistics, published information, and interviews with the fishers. Average catch per unit effort (CPUEs) were standardized by a generalized linear model (GLM) considering the effects of fishing year, season and landing area. Standardized CPUE of age-0 bluefin tuna showed larger fluctuations year by year than the nominal CPUE combined for all ages. High CPUEs in fishing years of 1981, 1994, 1996 and 1999 were observed. Data from these years agreed with the higher recruitments estimated by virtual population analysis (VPA) or higher catch of age-0 fish reported for the Pacific side. The age-specific standardized CPUE of age-0 bluefin tuna in this study was judged to be a useful indicator of recruitment.     

Primary structure and thermostability of bigeye tuna myoglobin in relation to those of other scombridae fish

ABSTRACT:   In the present study, the cDNA encoding myoglobin (Mb) of bigeye tuna Thunnus obesus was cloned and its amino acid sequence deduced in order to investigate the relationship between the primary structure and thermostability of scombridae fish Mb. An open reading frame of bigeye tuna Mb cDNA contained 444 nucleotides encoding 147 amino acids. The primary structure of bigeye tuna Mb was highly conserved when compared with those of bluefin tuna and yellowfin tuna Mb, the sequence identity being 95.2–100.0%. It also showed relatively high identity (82.3–89.1%) with the counterparts of scombridae fish. Myoglobin was then isolated from the dark muscle of four scombridae fish including bigeye tuna. Differential scanning calorimetry and circular dichroism measurements on these Mb revealed that the thermostability of bigeye tuna Mb was lowest and that of skipjack Katsuwonus pelamis Mb highest among the scombridae fish Mb examined. The α-helical contents of scombridae fish Mb at 10°C were in the range of 39.8–44.8%, clearly lower than that of horse Mb (55.3%), suggesting instability of fish Mb. The melting temperatures of these Mb fell in the range of 75.7–79.9°C, lower than that of horse Mb (84.2°C). These results strongly suggest the instability of fish Mb.