Molecular phylogeny of the rotifers with two Indonesian Brachionus lineages

The rotifer Brachionus plicatilis is an ecologically and commercially important species, and has been studied in various fields such as population dynamics, ecotoxicology and aging. However, recent studies have revealed that the B. plicatilis lineages involve an unknown number of cryptic species, and the group has been regarded as the Brachionus complex. One cause of this complicated taxonomy is the lack of surveys in the tropical zone, which is characterized by enormous species-richness. Accordingly, in this study we collected two Brachionus rotifers from the Sumatra and Sulawesi Islands, Indonesia, and determined their partial nucleotide sequences of mitochondrial DNA cytochrome c oxidase subunit I gene. Subsequently, we constructed molecular phylogenetic trees with fourteen species/lineages from four genera including the two Indonesian rotifers. The two Indonesian Brachionus rotifers were respectively found to be phylogenetically close to B. ibericus and B. rotundiformis. On the other hand, Japanese B. plicatilis was suggested to be phylogenetically closer to B. Manjavacas, which is proposed to be a new species, than to Spanish B. plicatilis. These results imply that the current taxonomy of the Brachionus is problematic, and a major revision is necessary to establish a reliable taxonomy of this group

Monitoring of the physiological status as the heat stress tolerance in the rotifer: a novel test for health diagnosis and ecological monitoring

To develop a simple method to evaluate physiological condition of the rotifer Brachionus plicatilis, important species as a live-food for aquaculture, we examined the heat stress tolerance using a household microwave oven. The rotifers were previously acclimated at each of 15°C, 20°C and 35°C, and exposed to heat treatment at every 10°C with the highest at 45°C. Subsequently, the animals were returned to the original temperature, and survival rates were recorded until 24 hours after the treatment. Under the 45°C-treatment, the animals acclimated at 15°C showed significantly lower survival rate (29%) than those at 25°C and 35°C with 75% and 84%, respectively. In contrast, under the treatments below 35°C, the survival rates were constant around 80% regardless of the acclimation temperature. These results suggest that the heat stress tolerance can be examined by the microwave oven, and the method will be useful at hatcheries for stable mass culture of the rotifer

Genotype analysis of commercial products of the soft seaweed Undaria pinnatifida (Laminariales, Alariaceae)

Genotypes of commercial products of the soft seaweed, Undaria pinnatifida, or wakame, were examined to evaluate if genetic analyses can be used with the processed materials, and to compare the genotypes from various localities. A total of 56 kinds of the commercial products (raw, boiled, salted, dried), and 3 aquaculture strains were used to amplify partial fragments of the COIII and RubisCO genes by PCR, and their DNA nucleotide sequences were determined. There were 9 and 3 haplotypes detected for the COIII and RubisCO genes, respectively, allowing separation of the specimens into 11 genotypes. The two most common genotypes where found in 31 and 14 products, while the other 9 genotypes where only found in 1–4 products. These results suggest that the genotype analysis can be used for any form of U. pinnatifida products and will be useful to develop a method to maintain the commercial value of U. pinnatifida made along the Sanriku Coast

Role of the cortisol on the onset of downstream migration in hatchery reared chum salmon Oncorhynchus keta fry

The relationship between downstream migration and plasma cortisol (F) level in chum salmon fry was investigated. The releases of chum fry (age 0, BW: 0.8.1.8 g) were carried out twice either in a day and a night. Approximately a million individuals of chum fry were released from the hatchery raceways to a hatchery pool, and the fry schools spontaneously moved down from the pool to the hatchery creek. The fish were sampled in the raceways (initial: before the migration), in the pool (staying: preparing period for the onset of migration), and in the creek (migrating: immediately after onset of the migration). The plasma concentrations of the migrating fry were significantly higher than those of the staying fry at 1 h after the releases in both the day- and the night-release. In addition, the F levels of the staying and migrating fry in the night-released were significantly higher than those of the day-released. Results can be interpreted that the F secretion ability may active with higher stress sensitivity in night. Chum fry show the downstream migration in nighttime in the early migratory season. Thus, the cortisol can relate to the onset of the downstream migration in the chum salmon fry

Life history patterns of silver eels Anguilla japonica collected in the Sanriku Coast of Japan

The migratory history in the silver eel stage of the Japanese eel, Anguilla japonica, collected in the mouth of Kozuchi River along the Sanriku Coast of Japan, was examined using the otolith microstructure and analysis of strontium (Sr) and calcium (Ca) concentrations with wavelength dispersive X-ray spectrometry by an electron microprobe. The line analysis of Sr :Ca ratios along the life history transect of each otolith showed a peak (ca 12-15×10<-3>), which corresponded to the period of their leptocephalus and early glass eel stages in the ocean. The mean Sr : Ca ratios from the elver mark to the otolith edge indicated that there were eels with several general categories of migratory history, that included sea eels that never entered freshwater (average Sr : Ca ratios, >_6.0×10<-3>) and others that had entered freshwater for brief periods, but returned to the estuary or bay. This evidence of the occurrence of sea eels in this northern area indicates that Japanese eels of the Sanriku Coast do not necessarily migrate into freshwater rivers during recruitment as glass eels at the beginning of their growth phase, and even those that do enter freshwater may later return to the marine environment

Role of the cortisol on the onset of downstream migration in hatchery reared chum salmon Oncorhynchus keta fry

The relationship between downstream migration and plasma cortisol (F) level in chum salmon fry was investigated. The releases of chum fry (age 0, BW: 0.8.1.8 g) were carried out twice either in a day and a night. Approximately a million individuals of chum fry were released from the hatchery raceways to a hatchery pool, and the fry schools spontaneously moved down from the pool to the hatchery creek. The fish were sampled in the raceways (initial: before the migration), in the pool (staying: preparing period for the onset of migration), and in the creek (migrating: immediately after onset of the migration). The plasma concentrations of the migrating fry were significantly higher than those of the staying fry at 1 h after the releases in both the day- and the night-release. In addition, the F levels of the staying and migrating fry in the night-released were significantly higher than those of the day-released. Results can be interpreted that the F secretion ability may active with higher stress sensitivity in night. Chum fry show the downstream migration in nighttime in the early migratory season. Thus, the cortisol can relate to the onset of the downstream migration in the chum salmon fry