Enoshima Aquarium

A stomach content analysis of 80 stranded and bycatch narrow-ridged finless porpoises in Ise and Mikawa Bays, central Japan, was conducted between 1992 and 2020. Prey items were identified in 76 samples. We combined three types of analyses to comprehensively explain their feeding habits: 1) numerical abundance and frequency of occurrence were used to analyze prey type utilization, 2) a combined rank index was used to search for important prey taxa, and 3) cluster analysis of flexible mixture modeling was used to detect the characteristics of feeding. Our results showed that the food habits of this population were characterized by frequent cephalopod and nektonic fish feeding and infrequent but large amount of benthic fish feeding. They changed their prey seasonally, where cephalopods were dominant during the spring-summer season. Cephalopods belonging to Teuthida and Octopoda, and fish belonging to Clupeiformes, Sillagidae, Gobiidae, and Callionymiae were suggested as important prey. We showed that in Ise and Mikawa Bays, porpoises likely feed opportunistically on various fish species and cephalopods.

Hofstenia Bock, 1923, the type genus of Hofsteniidae, was originally established for H. atroviridis Bock, 1923, from Misaki, Kanagawa Prefecture, Japan. This study describes Hofstenia sugashimaensis sp. nov., discovered in water tanks at the Sugashima Marine Biological Laboratory (Nagoya University) and Toba Aquarium, both situated at the mouth of Ise Bay in Mie Prefecture, along the Pacific coast of central Japan. Morphologically, it resembles H. miamia Corrêa, 1960 (commonly known as the “three-banded panther worm”) but is distinguished by two transverse bands and dorsal midline markings based on intra- and interspecific comparisons. Phylogenetic analysis of partial sequences of the cytochrome c oxidase subunit I, 18S rRNA, and 28S rRNA supports its genetic distinction from H. miamia.

Symbiosis with chemosynthetic bacteria is a biological phenomenon that has enabled animals to adapt to deep-sea environments. The deep-sea vent mussel Bathymodiolus septemdierum harbors sulfur-oxidizing symbionts in its gills, which serve as its main source of nutrients. However, the establishment and maintenance of this symbiosis process remain poorly understood, partly because culturing deep-sea mussels and their symbionts is difficult and experimental studies are rare. In the present study, we aimed to establish a rearing method for B. septemdierum and investigate the effects of sodium sulfide (Na2S) addition and gas concentration control in rearing tanks. Three tanks were prepared: a normal tank (tank N), one with Na2S (tank S), and one with Na2S and control dissolved oxygen (tank SO). Mussels were maintained for more than 1000 days, and host survival, gill histology, and the abundance of symbionts were investigated. In tanks N and S, symbionts were depleted within a short period, whereas in tank SO, gill morphology and symbiont abundance were maintained at levels comparable to those of freshly collected individuals, even after 1000 days. However, the survival rate of the host did not correspond to symbiont maintenance. Phylogenetic analysis revealed that the symbiont RuBisCO exists in Form II, which is generally adapted to low-O2 and high-CO2 environments. These results suggest that the long-term maintenance of B. septemdierum symbionts is possible by adding Na2S and controlling the dissolved gas concentration. Further improvements in rearing methods could contribute to a deeper understanding of host-symbiont interactions in this unique deep-sea organism.

The open ocean is a vast, highly connected environment, and the organisms found there have been hypothesized to represent massive, well-mixed populations. Of these, the man-o'-war or bluebottle (Physalia) is uniquely suited to long-distance travel, using its gas-filled float and muscular crest to catch the wind and sail the sea surface. We tested the hypothesis of a global, panmictic Physalia population by sequencing whole genomes of 151 samples and found five distinct lineages, with multiple lines of evidence indicating strong reproductive isolation, despite range overlap. We then scored thousands of images of Physalia uploaded to the citizen-science website inaturalist.org and identified four recognizable morphologies, described their geographical distribution, and linked them to four of the lineages that were identified with genomic data. We conclude there are at least four species, three of which correspond to species proposed by scientists in the 18th and 19th centuries, along with one newly named species, Physalia minuta Church and Dunn, sp. nov. Within each species, we observe significant population structure, with evidence of persistent subpopulations at a regional scale. We used ocean circulation modeling to show that these subpopulations align with predominant currents and winds. Our findings indicate that, even in these sailing species, genetic variation is highly partitioned across the open ocean.

ABSTRACTThis study revealed that 41.9% of wild‐born Japanese captive dolphins (18 out of 43 dolphins) have neutralizing antibodies specific to cetacean morbillivirus (CeMV). This finding indicates a widespread yet undetected CeMV infection among wild dolphins in the waters around Japan, occurring without notable epidemic or mass mortality of dolphins.

ABSTRACT Four Pseudarchasteridae species, including one new species, are described from Japanese waters. Paragonaster hoeimaruae Kobayshi sp. n. resembles two north-west Pacific congeners, P. chinensis and P. obtusus, but differs from these species in having pedicellariae and lateral abactinal series extending to less than one-half of arm length. We also report the first occurrence of Gephyreaster and P. stenostichus from Japanese waters. http://www.zoobank.org/urn:lsid:zoobank.org:pub:0B02F074-9B9A-4A87-A9D5-797740C6EE50

Active acoustic emission from a mother to a calf after parturition is one strategy used to enhance recognition of mothers by calves and develop, then maintain, a mother–calf bond from an early stage. This study predicted that a high-calling postpartum period exists in a social delphinid, the Pacific white-sided dolphin (Lagenorhynchus obliquidens). This species produces pulsed call sequences for vocal exchange with conspecifics, and these sequences appear to be an important signal between mothers and calves. Sounds were recorded from three pregnant females at the Niigata City Aquarium, Marinepia Nihonkai, Japan, before and after each birth in 2019, 2020, and 2021 to investigate the rate of their pulsed call sequences. Continuous data from prior to four days to five days following parturition, opportunistic data within the last pre-parturition month, and data from the postpartum period were obtained from the females. The pulsed call sequence gradually increased during the last gestational month. A high-rate sequence was repeated daily for four days pre-parturition and faded within several hours postpartum, and few sequences were produced from the day after parturition. Contrary to our prediction, the many pre-parturition sequences and fewer postpartum sequences suggest a low efficiency of postpartum imprinting in this species.

Vestimentiferan tubeworms are representative members of deep-sea chemosynthetic ecosystems. In this study, we developed a draft genome and gene models and performed genomic and transcriptomic analyses of Lamellibrachia satsuma, the only vestimentiferan reported from the euphotic zone. The quality of the genome assembly and gene models is comparable to or higher than those of previously reported vestimentiferan tubeworms. Tissue-specific transcriptome sequencing revealed that Toll-like receptor genes and lineage-specific expanded bacteriolytic enzyme genes are highly expressed in the obturacular and vestimental regions, respectively, suggesting the importance of these tissues in defense against pathogens. On the other hand, globin subunit genes are expressed almost exclusively in the trunk region, supporting the hypothesis that the trophosome is the site of haemoglobin biosynthesis. Vestimentiferan-specific expanded gene families included chitinases, ion channels, and C-type lectins, suggesting the importance of these functions for vestimentiferans. C-type lectins in the trunk region, in particular, may be involved in recognition of pathogens, or in interactions between tubeworms and symbiotic bacteria. Our genomic and transcriptomic analyses enhance understanding of molecular mechanisms underlying the unique lifestyle of vestimentiferan tubeworms, particularly their obligate mutualism with chemosynthetic bacteria.

Mycobacterium marinum is a slow-growing, photochromogenic nontuberculous mycobacterium, which can cause mycobacteriosis in various animals, including humans. Several cases of fish mycobacteriosis have been reported to date. Mycobacterium marinum has also been isolated from aquatic environmental sources such as water, sand, biofilms, and plants in the natural environments. Hence, we hypothesized that a wide variety of sources could be involved in the transmission of M.marinum. In this study, we tested this hypothesis by isolating M.marinum from various sources such as fish, invertebrates, seagrass, periphytons, biofilms, sand, and/or water in two aquaria in Japan and conducting a phylogenetic analysis based on single-nucleotide polymorphisms (SNPs) using whole-genome sequences of the isolated strains. The analysis revealed that the strains from animal and environmental sources belonged to the same clusters. This molecular-based study epidemiologically confirmed that various sources, including fish, invertebrates, and environmental sources, could be involved in transmission of M.marinum in a closed-rearing environment. This is the first report where M.marinum was isolated from different sources, and various transmission routes were confirmed in actual cases, which provided essential information to improve the epidemiology of M.marinum.