Growth rates, relative growth and a potential aging method using vertebral centra in Silurus biwaensis(Siluriformes: Siluridae)

Relative growth and relationship between age and growth in Silurus biwaensis were examined on the basis of the body size data of the catfish collected from Lake Biwa and the reared catfish which were hatched from artificially inseminated eggs. Although it had been reported that the proportion of head length to body length increased with growth in S. biwaensis, such a relationship was not found for 218 catfish that were examined in this study. On the other hand, the proportion of head length to head width significantly decreased with SL in females. This result indicated that the narrow head shape peculiar to S. biwaensis becomes slightly squarer in bigger females. The three catfish reared from the hatching grew to 196-410mm SL for 2.7 years (73-152mm/yr). This growth rate was in contrast with that of a tagged adult male, which grew only 50mm from 460mm SL to 510mm SL in the lake for two years (25mm/yr). These results suggested that the growth of the adults might extremely slow down after the fast growth at the immature stage. This study also reported that the number of transparent zones in vertebral centra of S. biwaensis increased with growth. The vertebral centrum may possibly be utilized as an age indicator for this species and the other kinds of Silurid

Growth rates, relative growth and a potential aging method using vertebral centra in Silurus biwaensis(Siluriformes: Siluridae)

Relative growth and relationship between age and growth in Silurus biwaensis were examined on the basis of the body size data of the catfish collected from Lake Biwa and the reared catfish which were hatched from artificially inseminated eggs. Although it had been reported that the proportion of head length to body length increased with growth in S. biwaensis, such a relationship was not found for 218 catfish that were examined in this study. On the other hand, the proportion of head length to head width significantly decreased with SL in females. This result indicated that the narrow head shape peculiar to S. biwaensis becomes slightly squarer in bigger females. The three catfish reared from the hatching grew to 196-410mm SL for 2.7 years (73-152mm/yr). This growth rate was in contrast with that of a tagged adult male, which grew only 50mm from 460mm SL to 510mm SL in the lake for two years (25mm/yr). These results suggested that the growth of the adults might extremely slow down after the fast growth at the immature stage. This study also reported that the number of transparent zones in vertebral centra of S. biwaensis increased with growth. The vertebral centrum may possibly be utilized as an age indicator for this species and the other kinds of Silurid

Large-scale hybridization of Japanese populations of Hinamoroko, Aphyocypris chinensis, with A. kikuchii introduced from Taiwan

Aphyocypris chinensis is a small cyprinid that is widely distributed in lowland areas of continental China, the Korean Peninsula, and the northwestern part of Kyushu, Japan. However, this species is severely threatened in Japan due to human impacts; thus, several facilities and citizen groups implemented captive breeding and reintroduction/reinforcement programs using several dozen founder fish collected from Tanushimaru, the location with the only known natural population, in the 1980s and 1990s. To determine the phylogenetic position and genetic authenticity of Japanese populations of A. chinensis, we conducted mtDNA and genome-wide SNP analyses using a total of 254 specimens from 31 wild and captive samples, including specimens of Chinese and Korean A. chinensis and the close relative A. kikuchii from Taiwan. The mtDNA divergence and phylogeny indicated that the haplotypes found exclusively in Japan were differentiated from the Chinese/Korean haplotypes (uncorrected p = 2.6% in the cytochrome b gene) to the same extent as they were from A. kikuchii haplotypes (p = 2.9%). Results from mtDNA sequences and 47–359 SNPs, obtained using the MIG-seq method with different parameter sets, revealed that the initial captive populations and an extinct wild population in Ukiha, adjacent to Tanushimaru, were genuine Japanese populations, whereas all extant captive and wild populations in Japan are hybrids between Japanese A. chinensis and A. kikuchii, or A. kikuchii itself. The details of the captive breeding and exchange programs, as well as evidence for the aquarium trade of A. kikuchii since the 1990s, strongly suggest that the mixture of A. kikuchii into Japanese populations occurred within the first several years of the establishment of captive populations in 1994. The present case of the highly probable extinction of genuine Japanese populations of A. chinensis emphasizes the importance of confirmation and management of the genetic authenticity of conservation-targeted species

Reassessment of Pigmentation Patterns used for Identifying Leptocephali (Gnathophis heterognathos and G. ginanago) Collected from the Kuroshio–Oyashio transition region

Identification of leptocephali of Gnathophis heterognathos and G. ginanago, the most abundant leptocephali in Japanese water, is usually identified based on morphological characteristics such as total number of myomeres (TM), number of myomeres of anterior to the last vertical blood vessel (VBV last) and presence or absence of melanophores on the lateral surface of the posterior spinal cord. However, because some of individuals collected in the Kuroshio–Oyashio transition region differed from the norm in the above characters, the validity of the last–mentioned was examined using the mitochondrial DNA 16S rRNA gene to provide genetic evidence. A total of 394 leptocephali were classified into following four morphotypes, Types A1 (TM: 117–128, VBV last: 36–44, pigmentation: absent, Body height (BH)/Total length (TL) ratio: 0.083–0.123), A2(TM: 119–126, VBV last: 40–44, pigmentation: present, BH/TL ratio: 0.082–0.127), B1(TM: 125–134, VBV last: 41–48, pigmentation: present, BH/TL ratio: 0.093–0.137) and B2(TM: 125–135, VBV last: 43–48, pigmentation: absent, BH/TL ratio: 0.080–0.139). Group A showed lower TM, VBV last, and BH/TL ratio than those of Group B. Molecular evidence confirmed that, Groups A (Types A1 and A2) and B (Types B1 and B2) were in fact G. heterognathos and G. ginanago, respectively. In addition, relationship of total length and pre–anal myomere (PAM)/TM ratio as an indicator of metamorphosis showed that the presence of posterior spinal cord melanophores was depended on their growth. These results indicate that Gnathophis leptocephali obtained from the Kuroshio–Oyashio transition region were comprising only the two species, and that variations in the pigmentation pattern characters rendered them unsuitable for identification purposes. Combination of above morphometric or meristic characters is effective for identified these two species