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Redescription of Bicotyle reticulata (Monogenea: Heteraxinidae) from Pampus punctatissimus (Scombriformes: Stromateidae) in the Seto Inland Sea, Japan
Get PDFBicotyle reticulata (Goto, 1894) (Monogenea: Heteraxinidae) is redescribed from the gills of Pampus punctatissimus (Temminck and Schlegel, 1845) in the Seto Inland Sea, Japan. Although its taxonomic position had been frequently revised, B. reticulata remains solely documented from the original description, 130 years ago. The present study revealed that B. reticulata exhibits subsequent diagnostic characters of Bicotyle Tripathi, 1956: clamps on either side of the haptor unequal in size and number, the genital atrium armed with several spines, and a convoluted germarium. The phylogenetic analysis based on 28S rDNA sequences suggests that B. reticulata and Heteraxinidae constitute a monophyletic group. All currently known species of Bicotyle are listed, and a key to six species of the genus is provided.journal articl
How much light intensity to induce repulsion or attraction behaviour in juvenile salmon?
Get PDFTechniques to control the phototactic behaviour of fish have expanded with progress in LED lights. However, the phototaxis direction of fish could be reversible at some light intensities, and thus it is necessary to evaluate the light-intensity levels that will induce repulsion or attraction behaviour to understand the transition. This study determined the light intensities of white LED light required to induce repulsion or attraction behaviour from a dark place, and the degree of dark-adapted visual sensitivity in juvenile of two salmon species. Oncorhynchus keta smolts showed negative phototaxis under intense light intensity, but positive phototaxis was not observed. The range of light intensities under which O. masou exhibited positive phototaxis changed with the life stage (from pre-smolts to smolts). Notably, the light intensities that elicited positive phototaxis were relatively low and narrow for pre-smolts, whereas smolts responded to a greater range of intensities. Positive phototaxis disappeared in O. masou pre-smolts under intense light intensity, but not in O. masou smolts under the most-intense light intensity tested here. Negative phototaxis was not observed in O. masou pre-smolts or smolts. The appropriate light intensity indicated here may be used to either guide juvenile O. masou from the dam reservoir to fishways or bypass channels, or to repel O. keta smolts from the water intakes of agricultural diversion weirs or hydropower dams.journal articl
Nocturnal substrate association of four coral reef fish groups (parrotfishes, surgeonfishes, groupers and butterflyfishes) in relation to substrate architectural characteristics
Get PDFAlthough numerous coral reef fish species utilize substrates with high structural complexities as habitats and refuge spaces, quantitative analysis of nocturnal fish substrate associations has not been sufficiently examined yet. The aims of the present study were to clarify the nocturnal substrate associations of 17 coral reef fish species (nine parrotfish, two surgeonfish, two grouper and four butterflyfish) in relation to substrate architectural characteristics. Substrate architectural characteristics were categorized into seven types: (1) eave-like space, (2) large inter-branch space, (3) overhang by protrusion of fine branching structure, (4) overhang by coarse structure, (5) uneven structure without large space or overhang, (6) flat and (7) macroalgae. Overall, fishes were primarily associated with three architectural characteristics (eave-like space, large inter-branch space and overhang by coarse structure). The main providers of these three architectural characteristics were tabular and corymbose Acropora, staghorn Acropora, and rock. Species-specific significant positive associations with particular architectural characteristics were found as follows. For the nine parrotfish species, Chlorurus microrhinos with large inter-branch space and overhang by coarse structure; Ch. spilurus with eave-like space and large inter-branch space; Hipposcarus longiceps with large inter-branch space; Scarus ghobban with overhang by coarse structure; five species (Scarus forsteni, S. niger, S. oviceps, S. rivulatus and S. schlegeli) with eave-like space. For the two surgeonfish species, Naso unicornis with overhang by coarse structure; N. lituratus with eave-like space. For the two grouper species, Plectropomus leopardus with eave-like space; Epinephelus ongus with overhang by coarse structure. For the four butterflyfish species, Chaetodon trifascialis with eave-like space and large inter-branch space; C. lunulatus and C. ephippium with large inter-branch space; C. auriga showed no significant associations with any architectural characteristics. Four species (Ch. microrhinos, H. longiceps, S. niger and N. unicornis) also showed clear variations in substrate associations among the different fish size classes. Since parrotfishes, surgeonfishes and groupers are main fisheries targets in coral reefs, conservation and restoration of coral species that provide eave-like space (tabular and corymbose Acropora) and large inter-branch space (staghorn Acropora) as well as hard substrates with coarse structure that provide overhang (rock) should be considered for effective fisheries management in coral reefs. For butterflyfishes, coral species that provide eave-like space (tabular Acropora) and large inter-branch space (staghorn Acropora) should also be conserved and restored for provision of sleeping sites.journal articl
Length estimation of fish detected as non-occluded using a smartphone application and deep learning method
Get PDFUncertainty in stock assessment can be reduced if accurate and precise length composition of catch is available. Length data are usually manually collected, although this method is costly and time-consuming. Recently, some studies have estimated fish species and length from images using deep learning by installing camera systems in fishing vessels or a fish auction center (Álvarez -Ellacuria et al., 2020; Lekunberri et al., 2022; Ovalle et al., 2022; Palmer et al., 2022). Once a deep learning model is properly trained, it does not require expensive and time-consuming manual labor. However, several studies on the deep learning models had monitoring fishing practices using electronic monitoring systems; therefore, it is necessary to solve many issues, such as counting the total number of fish in the catch. In this study, we proposed a new deep learning-based method to estimate fish length using images. Species identification was not performed by the model, and images were taken manually by the measurers; however, length composition was obtained only for non-occluded fish detected by the model. A smartphone application was developed to calculate scale information (cm/pixel) from a known size fish box in fish images, and the Mask R-CNN (Region-based convolutional neural networks) model was trained using 76,161 fish to predict non-occluded fish. Two experiments were conducted to confirm whether the proposed method resulted in errors in the length composition. First, we manually measured the total length (TL) for four species and one genus (categories), estimated the TL using a deep learning method, and calculated the bias. Second, multiple fish in a fish box were photographed simultaneously, and the relative difference between the mean TL estimated from the non-occluded fish and the true mean TL from all fish was calculated. The results showed that the biases of all five categories were from −0.69 cm to 0.37 cm and the range of difference was from −1.14 % to 1.40 % regardless of the number of fish in the fish box. The deep learning method was used not to replace the measurer but to increase their measurement efficiency. The proposed method is expected to increase opportunities for the application of deep learning-based fish length estimation in areas of research that are different from the scope of conventional electronic monitoring systems.journal articl
Settlement and ovigerous season of sand shrimp Crangon uritai in the central Inland Sea, Japan
Get PDFSand shrimp Crangon uritai is distributed in shallow waters including the intertidal zone in eastern Asia and is known to be a prey item and a predator of juveniles of commercially important fishes. Specimens were collected on the Kawaradzu tidal flat, using a rake sledge net (mesh size 2.0 mm) from June to December 2016 and 2017, and in the adjacent shallow bottom (3–4 m depth at high tide) using a sledge net (mesh size 0.76 mm) from January to August 2018 and 2019. Seasonal changes in the density index and carapace length distribution were studied in both sites. The frequency of ovigerous females were indicated for the tidal flat. Settlement mainly occurred from May to July although low intensity settlement seemed to occur throughout the year except for September and October. Ovigerous season in the tidal flat finished in August or September by disappearance of the cohort including ovigerous females and resumed in October with the oviposition of 0-year individuals. Ovigerous females might occur throughout the year except for August or September, although their occurrence was not checked in the shallow bottom. Research on the offshore area is needed to detail the whole life history.journal articl
Effect of a long photoperiod on the timing of spawning in the Pacific bluefin tuna, Thunnus orientalis
Get PDFIn this study, we examined the effects of a long photoperiod on the reproduction of Pacific bluefin tuna (Thunnus orientalis) in a land-based tank. Three-year-old fish were shifted from a short (10.5 L:13.5D) to long (15 L:9D) photoperiod in December. The broodstocks exhibited gonadal development after this photoperiod change and spawned spontaneously the following March, approximately three months earlier than the normal spawning season. Although the results were based on data from a small sample size of fish, the study suggests that a long photoperiod induces the onset of gonadal development in Pacific bluefin tuna, thereby accelerating their spawning time.journal articl
New Japanese Record of Henneguya postexilis (Cnidaria: Myxobolidae) from Gills of Alien Channel Catfish Ictalurus punctatus (Siluriformes: Ictaluridae) in Japan
Get PDFHenneguya postexilis Minchew, 1977 (Cnidaria: Myxobolidae) is described as a novel record for Japan. It was found in the gills of non-native Ictalurus punctatus (Rafinesque, 1818) (Siluriformes: Ictaluridae), which were collected from the Omoi River, a tributary of the Tone River system in Tochigi Prefecture, central Honshu. This myxozoan species is native to North America and its discovery from Japan in this study is the second case reported from a non-native region. Until now, H. postexilis has only been observed in I. punctatus, suggesting that it is an introduced alien species in Japan, likely accompanying its host.journal articl
Assessing Molecular Localization of Symbiont Microalgae in Coral Branches Through Mass Spectrometry Imaging
Get PDFReef-building corals are a fundamental pillar of coral reef ecosystems in tropical and subtropical shallow environments. Corals harbor symbiotic dinoflagellates belonging to the family Symbiodiniaceae, commonly known as zooxanthellae. Extensive research has been conducted on this symbiotic relationship, yet the fundamental information about the distribution and localization of Symbiodiniaceae cells in corals is still limited. This information is crucial to understanding the mechanism underlying the metabolite exchange between corals and their algal symbionts, as well as the metabolic flow within holobionts. To examine the distribution of Symbiodiniaceae cells within corals, in this study, we used fluorescence imaging and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MS-Imaging) on branches of the Acropora tenuis coral. We successfully prepared frozen sections of the coral for molecular imaging without fixing or decalcifying the coral branches. By combining the results of MS-Imaging with that of the fluorescence imaging, we determined that the algal Symbiodiniaceae symbionts were not only localized in the tentacle and surface region of the coral branches but also inhabited the in inner parts. Therefore, the molecular imaging technique used in this study could be valuable to further investigate the molecular dynamics between corals and their symbionts.journal articl