Kazuhiko Anraku

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

SUMMARY 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.

Near-ultraviolet radiation guides the emerged hatchlings of loggerhead turtles Caretta caretta (Linnaeus) from a nesting beach to the sea at night

Hatchling sea turtles (Caretta caretta) emerge from their beach nests at night and crawl seaward immediately, even where the sea is not visible to them. This sea-finding ability of hatchlings is one of the outstanding phenomena of animal orientation. The primary sea-finding mechanism is an orientation towards light, and blindfolded hatchlings could not find the sea. Hatchlings of loggerhead turtles avoid yellow and orange light and are strongly attracted to light in the near-ultraviolet to green part of the spectrum. Here we demonstrate in experiments at a nesting beach that (1) loggerhead hatchlings orient to near-ultraviolet radiation, and (2) the intensity of near-ultraviolet radiation is always higher seaward than landward on all nights. These results are consistent with long-term monitoring data that show emergence of loggerhead hatchlings takes place during any phase and position of the moon. To prevent mis-orientation of hatchlings, roads, and human settlements fronting turtle nesting beaches should use lights that do not emit near-ultraviolet radiation.

Sound generated by a payao and comparison with auditory sensitivity of jack mackerel Trachurus japonicus

Sound generated by a payao, an anchored bamboo fish aggregating device, is believed to be attractive to fish; but until now, there is no available record of payao-generated sound. This study presents payao-generated sound recorded by a hydrophone at water depths of 5, 10 and 15 m from a fixed distance of 3 m relative to the payao, and compares the sound with the auditory sensitivity of jack mackerel Trachurus japonicus measured at discrete frequencies from 100 to 2000 Hz using the auditory brainstem response protocol. A consistent peak appeared in the sound spectrum at 49 Hz and showed an increasing sound pressure level with depth, which suggests that payao sound may come from the anchor rope. However, the contribution of the bamboo raft can not yet be discounted. The hearing threshold curve indicated that the most sensitive frequency range in jack mackerel is from 92.1 dB at 800 Hz to 111.0 dB at 200 Hz. These results show that the dominant frequency range of payao sound does not correspond with the high sensitivity frequency range of fish hearing.

Sustainability of fishers’ communities in tropical island fisheries from the perspectives of resource use and management: a comparative study of Pohnpei (Micronesia), Mafia (Tanzania), and Guimaras (Philippines)

AbstractThe fisheries structure, fishing gear, fishing vessels and their ownership, landing sites and markets, as well as fisheries management and fishers’ participation were surveyed in three tropical islands: Pohnpei (Micronesia), Mafia (Tanzania), and Guimaras (Philippines), covering 127 fishers. Labour-intensive gear, including purse seines and ring nets, characterised Mafia fisheries. Fibre-reinforced plastic (FRP) boats characterised Pohnpei fisheries, and canoes with nonmarine engines were characteristic of Guimaras fisheries. Wooden plank boats with large crews were only seen in Mafia. From a gear/vessel ownership perspective, the fisher categories present were gear fishers, gear-vessel fishers, employers, and casual labour fishers. Casual labour fishers and employers were only apparent in Mafia. The fisheries in Pohnpei had a relatively early age of entry, which was attributed to the urban markets available and family cohesion, while community organisation-based management of these fisheries was weak. Mafia and rural Guimaras fishers depended on middlemen, due to the distance of the market. Deteriorating subsistence-related fishery dependency means that the Guimaras fishers’ community is at risk. The high shared gear/vessel ownership rates and levels of affiliation to community organisations in Mafia reflect government’s timely community sustainability enhancement initiative. Based on our analyses, we propose the “fishers’ community sustainability” concept. The sustainability of a fisher’s community can be judged on (1) the age of entry to the fisheries, (2) the monetary profits made at fish markets and through marketing, (3) the cohesion among the fishers, and (4) the level of subsistence-related dependency on the fishery. The fishery is key to community sustainability, thus ensuring fishery-dependent life. It is essential to consider the above indicators of fishers’ community sustainability during fisheries development.

Ontogenetic eye development and related behavioural changes in larvae and juveniles of barramundi Lates calcarifer (Bloch)

Larvae and juveniles of barramundi Lates calcarifer (Bloch) were examined for the development of the retina, occurrence of the retinomotor response and retinal tapetum and change in eye size with age in days. The barramundi hatched with unpigmented non-functional eyes in which retinal cells had not yet differentiated into the various elements. Soon it was followed by rapid changes in the histology of the retina. Two-day-old larvae had a well-pigmented retina with area temporalis which would allow acute vision and prey attack in the nasal direction. At 10 days, rod cells and the retinal tapetum first appeared in the retina and the retinomotor response first occurred; these would allow feeding in dim light. The retinal tapetum moved in unison with the cones and the pigment epithelium during the retinomotor response. At 26 days, the horizontal cells were divided into two layers and the twin cones appeared. These changes in the eyes occurred concurrently or in anticipation of behavioural changes, such as the onset of the first feeding at 2 days, the shift of habitat from coastal waters to swamps at the notochord flexion stage at 7–15 days, the abrupt change in feeding behaviour from roving zooplanktivore to lurking predator at 25–30 days and a later shift of habitat from turbid swamps to open coastal or lake areas at the early juvenile stage.

Differentiation of Visual Spectra and Nuptial Colorations of Two ＂Paratanakia Himantegus＂ Subspecies (Cyprinoidea: Acheilognathidae) in Response to the Distinct Photic Conditions of Their Habitats

BackgroundVision, 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.ResultsThe electroretinogram (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.ConclusionsTwo 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 gender identification.

Differences in olfactory system between wild and cultured red sea bream, Pagrus major (Teleostei)

A four-month market survey revealed that at some mariculture centers in Japan, over 90% of red sea bream reared in captivity possess a deformed single nasal opening as compared with normal fish with anterior and posterior nasal openings at each olfactory organ. The deformity occurred at day 32-40 after hatching when the medial and lateral epidermal lips failed to form the septum that separates both olfactory nares. The authors also demonstrated that the fish reared in captivity have no problems feeding on pelleted diet but their wild counterparts do not accept non-living food even under a long period of starvation. Differences in olfactory system between wild and cultured fish are discussed especially in reference to the olfactory system and fish behavior.

Response to ‘Not-so-simple setae’

In his Correspondence article ([p. 871][1]), DeForest Mellon, Jr argues that the type of seta in our report ([Monteclaro et al., 2010][2]) was erroneously identified. In response, we would like to make the following remarks. Stimulation of an antennule that was either seta-less or without plumose

Swimming Behavior of Juvenile Yellowfin Tuna (Thunnus albacares) Around Fish Aggragate Devices (F.A.D.S) in the Philippines

Three juvenile yellowfin tuna (22–26 cm FL) were monitored around a payao (FAD: Fish Aggregating Device) in Panay Gulf, the Philippines. A receiver was attached to the anchor line of the payao, and ultrasonic transmitters were implanted into the abdominal cavities of the fish. Juvenile yellowfin tuna swam within a limited shallow range during nighttime and dived to deeper waters, maximum 105 m, during daytime, then moved away from the payao at midnight. One juvenile yellowfin tuna was recaptured 2 days after release by handline in the same payao, and two juvenile yellowfin tuna were recaptured 12 days after release by ringnet in another payao over 3 km away. These recaptures indicate that the fish were active enough to feed and swim, and also show the feasibility of undertaking telemetry studies on juvenile yellowfin tuna.