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We validated the daily formation of increments in otoliths of yellow goosefish Lophius litulon using reared individuals to examine the growth in the field. Single, round-shaped core structures were observed in 41% of sagittae and in 73% of the lapilli. Therefore, lapillar otoliths were used for further observations of daily increment analysis. The lapillus radius of newly hatched larvae was 15.0 ± 1.4 μm (mean ± standard deviation) forming the hatch check (first check). At 6 days after hatching (DAH), the second check was observed, which may correspond to the energy transition from endogenous to exogenous nutrition, located at 28.1 ± 0.7 μm from the core structures. Thereafter, clear daily increments formed outside the check. To estimate larval growth in the field, we examined the relationship between the notochord length (NL) and lapillus radius by an allometric equation. The mean growth rate was estimated as ca. 0.18 mm in NL/day during 10–40 DAH. The results of this study provide insights into the previously unknown early life history and will enable further understanding of the population dynamics of the genus Lophius.

We developed a novel molecular genetic method using restriction fragment length polymorphisms (RFLPs) to identify the taxonomically debatable Japanese sand lances of the genus Ammodytes. Partial nucleotide sequences of the mitochondrial DNA cytochrome c oxidase subunit 1 (COI) gene of Ammodytes japonicus (n = 405), Ammodytes heian (n = 284), and Ammodytes hexapterus (n = 15) were determined and found to contain species-specific restriction sites for HindIII-HF and RsaI enzymes. The observed RFLP patterns from a combination of two enzymes were specific in each species except for specimens with rare haplotypes of A. japonicus (1.5 %) and A. heian (2.1 %), whereas detailed morphological analysis using 29 characters failed to discriminate the COI-identified specimens of these two species collected from the same locality. The developed molecular method will allow rapid and precise identification of the Japanese sand lances, especially for the sympatric A. japonicus and A. heian, thereby providing a reliable means for ecological research and stock management of these species.

Vertebrate troponin regulates muscle contraction through alternative binding of the C-terminal region of the inhibitory subunit, troponin-I (TnI), to actin or troponin-C (TnC) in a Ca(2+)-dependent manner. To elucidate the molecular mechanisms of this regulation by molluskan troponin, we compared the functional properties of the recombinant fragments of Akazara scallop TnI and rabbit fast skeletal TnI. The C-terminal fragment of Akazara scallop TnI (ATnI(232-292)), which contains the inhibitory region (residues 104-115 of rabbit TnI) and the regulatory TnC-binding site (residues 116-131), bound actin-tropomyosin and inhibited actomyosin-tropomyosin Mg-ATPase. However, it did not interact with TnC, even in the presence of Ca(2+). These results indicated that the mechanism involved in the alternative binding of this region was not observed in molluskan troponin. On the other hand, ATnI(130-252), which contains the structural TnC-binding site (residues 1-30 of rabbit TnI) and the inhibitory region, bound strongly to both actin and TnC. Moreover, the ternary complex consisting of this fragment, troponin-T, and TnC activated the ATPase in a Ca(2+)-dependent manner almost as effectively as intact Akazara scallop troponin. Therefore, Akazara scallop troponin regulates the contraction through the activating mechanisms that involve the region spanning from the structural TnC-binding site to the inhibitory region of TnI. Together with the observation that corresponding rabbit TnI-fragment (RTnI(1-116)) shows similar activating effects, these findings suggest the importance of the TnI N-terminal region not only for maintaining the structural integrity of troponin complex but also for Ca(2+)-dependent activation.