Seasonal Changes in the Tetrodotoxin Content of the Flatworm Planocera multitentaculata.

Tetrodotoxin (TTX) is a potent neurotoxin that acts specifically on voltage-gated sodium channels on excitable membranes of muscle and nerve tissues. The biosynthetic process for TTX is unclear, although marine bacteria are generally thought to be the primary producers. The marine flatworm Planocera multitentaculata is a known TTX-bearing organism, and is suspected to be a TTX supplier to pufferfish. In this study, flatworm specimens were collected from an intertidal zone in Hayama, Kanagawa, Japan, the TTX content of the flatworm was measured using liquid chromatography with tandem mass spectrometry (LC-MS/MS), and seasonal changes in TTX content were investigated. No significant difference in TTX concentration of the flatworm body was found between the spawning period and other periods. However, the TTX content in individual flatworms was significantly higher in the spawning period than at other times. The TTX content rose in association with an increase in the body weight of the flatworm.

Species composition of the genus Scombrops (Teleostei, Scombropidae) in the waters around the Japanese Archipelago: detection of a cryptic species.

Current literature states that family Scombropidae consists of a single genus Scombrops comprising three species worldwide, with two of them, Scombrops boops and Scombrops gilberti, distributed in the waters around the Japanese Archipelago. Although these two scombropids are commercially important species, little is known about the ecology of these fishes. It is difficult to discriminate between these two species based on external characteristics because of their morphological similarity. Here, we report two different morphotypes characterized by the relative growth between the otolith size and the standard length (SL) of the scombropid specimens caught in southern waters off Kyushu Island, Japan, and show the genetic relationship between the morphotypes by means of phylogenetic analyses using complete DNA sequences of the cytochrome b gene. The relationship between otolith weight and SL was significantly different between specimens < 505 mm SL and those > 550 mm SL. Phylogenetic analysis demonstrated that the sequences from these scombropid specimens formed three clades: two corresponded to S. boops and S. gilberti, while the third did not correspond to any sequence recorded in databases, suggesting that these specimens are undescribed scombropid species. Almost all the specimens with SL < 505 mm (n = 76) were identified as S. boops, and only nine as S. gilberti. On the other hand, almost all the specimens with SL > 550 mm (n = 41) fell in the unidentified group except for four specimens, whose sequences were identical to that of S. boops.

Phylogenetic position of Scombropidae within teleostei: the complete mitochondrial genome of the gnomefish, Scombrops gilberti.

The complete mitochondrial genome of the Japanese gnomefish, Scombrops gilberti, was determined using a PCR-based method. The total length of mitochondrial DNA (mtDNA) is 16 518 bp, which includes 13 protein-coding genes, two ribosomal RNA (rRNA) genes, 22 transfer RNA (tRNA) genes, and one control region. The mitochondrial gene arrangement of S. gilberti was found to be identical to that of other scombropid and indeed, other teleosts as well. Maximum likelihood analysis revealed that Scombropidae forms a sister group to Pempheriformes.

The complete mitochondrial genome of the gnomefish Scombrops boops (Teleostei, Perciformes, Scombropidae) from the Pacific Ocean off the Japanese Islands.

The complete mitochondrial genome of the gnomefish Scombrops boops was determined by a PCR-based method. The total length of mitochondrial DNA (mtDNA) was 16,517 bp, including 13 protein-coding genes, two ribosomal RNA genes, 22 transfer RNA genes and one control region. The mitochondrial gene arrangement of the gnomefish mtDNA was identical to those of typical teleosts. This is the first report of the complete mitochondrial genome of a member of the Scombropidae family and will be useful for the development of molecular tools for ecological research.

Variations in bile tolerance among Lactococcus lactis strains derived from different sources.

Lactococcus lactis subsp. lactis has been isolated from the intestines of marine fish and is a candidate probiotic for aquaculture. In order to use the bacterium as a probiotic, properties such as bile tolerance need to be assessed. Here, we compared bile tolerance in L. lactis strains derived from different sources. Three L. lactis subsp. lactis strains from marine fish (MFL), freshwater fish (FFL), and cheese starter (CSL) were used along with an Lactococcus lactis subsp. cremoris strain from cheese starter (CSC). The four strains were grown under various culture conditions: deMan-Rogosa-Sharpe (MRS) broth containing bile salts/acids, MRS agar containing oxgall, and phosphate-buffered saline (PBS) containing fish bile. Survival/growth of the strains in the presence of sodium cholate and sodium deoxycholate varied in the order MFL, CSL > CSC > FFL; in the presence of sodium taurocholate, the order was MFL > CSL > CSC > FFL. In liquid media containing various concentrations of oxgall, survival of the strains was observed in the order MFL > CSL > FFL and CSC. The survival of MFL was not affected by bile collected from the goldfish (Carassius auratus subsp. auratus) or the puffer fish (Takifugu niphobles), although the other strains showed significant inhibition of growth. It is a novel and beneficial finding that MFL has the highest resistance to bile acid.