Fisheries Science

Twenty-eight immature hatchery-reared Mekong giant catfish Pangasianodon gigas tagged with acoustic transmitters were released in the Mekong River, Thailand from 2002 to 2004. Twenty-four and four fish were tagged with normal transmitters and pressure-sensitive transmitters, respectively. Five to seven automated monitoring receivers were used for monitoring the post-release movements. The tagged catfish could be detected for up to 97 days, the first detection taking place at the release point, where the fish remained for several days. Sixteen tagged fish (57%) were not detected at any later point. These fish may have passed along the opposite (Laos) side of the river without notice because the width of the river was larger than the detection range of the transmitter. The remaining 12 tagged fish (43%) could be detected by the receivers installed, excluding the release point receiver. Of these 12 tagged fish, six showed long-distance (30–80 km) upstream movements and one long-distance (50 km) downstream movement. These seven fish (25%) were detected only during the daytime, suggesting that the Mekong giant catfish is diurnal.

Vibrio cholerae and V. vulnificus are of major concern due to their effect on public health throughout the world. It is therefore imperative to identify a gene and method that are suitable for the accurate species-specific detection of these two species. A duplex polymerase chain reaction (PCR) assay was developed using two sets of primers targeting the groEL gene for the accurate simultaneous detection of V. cholerae and V. vulnificus. The nucleotide sequence of the groEL gene was compared with the sequences of other Vibrio and non-Vibrio species. The specificity of two primer sets for duplex PCR was checked using 24 Vibrio and 8 non-Vibrio species. The primer sets were found to be specific for these two species and could detect both of the target bacterial species without any ambiguity, even when comparing closely related species. For both species, the detection limit was 100 pg of purified genomic DNA. The duplex PCR showed high specificity and sensitivity for each species and was sufficient for the detection of V. cholerae and V. vulnificus from artificially infected shellfish tissue, flounder, and even inoculated seawater. This method is simple and cost-effective, and can be utilized for the simultaneous detection of both species, thus representing an effective tool for both epidemiologist and ecologist.

Microstructures of sagittae and lapilli were examined in relation to somatic growth for reared larvae and juveniles of Pacific cod. The Laird-Gompertz model was fitted to the daily age and somatic growth relationship. Growth increments were deposited on a daily basis in both kinds of otoliths, with a check formed at hatching. Two subsequent checks and an accessory primordia (AP) occurred in the sagittae. The lapillus was adequate for increment width measurement through the early life stages. Sagittal and frontal plane of sagitta was adequate for measurement in the pre-AP and post-AP formation stages, respectively. The shift of desirable plane was caused by changes in otolith and increment shapes with AP formation. Back-calculated total lengths using the biological intercept method did not significantly differ with certain body lengths (P>0.05), suggesting validity of back-calculation in this species. Using the back-calculated total length, morphological and ecologic changes that seemed to affect checks and AP formations are discussed.

Artificially hatched Seriola species have the problem of malformation, mainly in their vertebrae, head, and mouth parts. To clarify the cause of vertebral malformation, the effects of hypoxia during embryogenesis on the induction of centrum defects was investigated in artificially hatched amberjack Seriola dumerili. Firstly, 7-somite stage embryos were exposed to waters of 0, 12.5, 25, 50, and 100% dissolved oxygen (DO) for 0.5, 1, 2, 3, 4, and 5 h to confirm the effective dose (DO concentration and duration of exposure) of hypoxia that induces somitic disturbances in newly hatched larvae. Exposure of embryos to 12.5% DO concentration for longer than 0.5 h induced somitic disturbances. Following this result, centrum defects in juveniles were investigated by an induction experiment with embryos exposed to 12.5% DO for 2 h at the gastrula, 1- or 2-somite, 10-somite, 15-somite, or heart beating stage. This experiment revealed that centrum defects were induced only during somitogenesis, and somitic disturbances were the premonitory symptom of centrum defects. These results indicate hypoxia during somitogenesis as a possible cause of centrum defects in amberjack.

The present study aimed to investigate a suitable anesthesia protocol for nutritional studies, fasting tolerance, and nutrient requirements for maintenance in juvenile northern bluefin tuna Thunnus orientalis weighing 0.8–0.9 g. The fish grew in a mass seedling production under completely controlled aquaculture. The solution of 0.2 mL 2-phenoxyethanol/L prepared by filtered seawater has been notably estimated as a anesthesia protocol for the juvenile, due to a shorter mean time necessary for anesthesia and recovery and higher survival rate at 24 h after recovery. All other anesthetics, 0.1 and 0.3 mL 2-phenoxyethanol/L, 0.05, 0.1 and 0.2 mL 4-allyl-2-methoxyphenol/L, and cool water temperature shocks at 16.8, 12.6 and 10.4°C, were inferior. In a 5-day tolerance test, the juvenile was fed sand lance Ammodytes personatus through the rearing period or fasted for 2, 3, 4 and 5 consecutive days. Survival rates were about 80 or 60, 50, 10 and 0%, respectively. From the relationships between days fasting and energetic and nutritional retentions, juvenile tuna require about 142.7 kJ, 5.46 g protein and 0.44 g fat/kg body weight a day for maintenance, indicating remarkably higher requirements than other aquaculture fish.

Little information exists on the gonadal development and maturity scale of Octopus ocellatus, an economically important octopus species commonly found in the west Pacific Ocean. A total of 171 O. ocellatus samples were collected monthly off the coast of northeast China (Qingdao, Shandong) from December 2011 to November 2012. Total body weight, mantle length, gonadosomatic index, and reproductive tract parameters of the samples were analyzed in males and females. The process of gonadal development in O. ocellatus was defined based on gonadal histological examination. Nine stages of oocyte development were identified during oogenesis, and a maturity scale of five stages (immature, developing, maturing, mature, and spent) was proposed for both ovary and testis. Additionally, the maturation status and dominant germ cell types of O. ocellatus in relation to monthly variation were identified. The seasonal changes showed that O. ocellatus off the coast of Qingdao is a fast-growing species with a short life span, which reproduces only once in a lifetime and then dies. Its reproductive cycle can be divided into four periods, beginning with the breeding period from April. Males become sexually mature in a smaller size than females, indicating that the mating behavior occurs early with sperm stored in the oviductal glands of the females before fertilization and spawning. This work contributes to the understanding of the maturation process in O. ocellatus, laying a foundation for further study on the mechanism of sperm storage in female octopuses and providing a reference for artificial breeding and fisheries impact assessment of this species.