Mid-water trawl surveys were conducted from late August to late September in 1999 and 2004 in order to investigate the distribution pattern, hatch date, and growth of juvenile Pacific bluefin tuna Thunnus orientalis in the Sea of Japan. Juveniles were collected at the stations where ambient water temperature (mean water temperature from surface to 30 m deep, WT0-30) was 23.4-25.9°C, and most of them were found in waters where WT0-30 was higher than 24°C. Sampled juveniles ranged 108-280 mm fork length. Based on otolith analysis, they were estimated to grow to approximately 180 and 250 mm at 60 and 90 days old, respectively, and showed similar growth to that of Atlantic bluefin tuna in the Mediterranean Sea. The back-calculated hatch date of the samples was mostly in July and most juveniles spawned in the Sea of Japan.

Taiwanese longline (LL) fisheries operating in the Indian Ocean usually target albacore tuna (ALB), swordfish (SWO) and yellowfin tuna (YFT) using regular LL. Bigeye tuna (BET), however, is targeted using deep LL. Thus, these two types of LL are considered to be different gears as they target different tuna species. Regular or deep LL fishing is defined by number of hooks per basket (NHB): regular LL if 6 ≤ NHB ≤ 10 and deep LL if 11 ≤ NHB ≤ 20. However, NHB information was available in only some of the recent LL data (1995)(1996)(1997)(1998)(1999). This situation had caused problems of biased results in stock analysis in the past. Thus, the objective of our study was to explore an effective method to separate the two types of LL fishing by considering species composition. Some intervals of BET catch ratios were found to be effective in separating the regular and deep LL catches, i.e. 0.0 ≤ BET/(BET + ALB + SWO) ≤ 0.4 and 0.8 ≤ BET/(BET + ALB) ≤ 1.0, respectively. Using these two separators, the LL known data set (1995)(1996)(1997)(1998)(1999) (learning data set) was classified. Correct classification occurred in 67.7% of the data, while 23.1% of the data were unclassified (11.9% due to zero catches and 11.2% due to classification into both LL types), and 9.2% were misclassifications. Then, using the methods developed, the LL unknown data set in the historical data was classified and nominal CPUE values were calculated for four species. The CPUE trends based on this study were likely to be more reliable than those of previous studies.KEY WORDS: bigeye tuna catch ratios, Indian Ocean, regular and deep tuna longline, separators.

We observed the growth, morphological changes, and behavior of larvae and juveniles of the Amazonian substrate-brooding cichlid discus fish Symphysodon aequifasciatus under laboratory conditions. The mean body length (BL) of newly hatched larvae was 3.4-3.5 mm, and the yolksac extended to approximately 42 % of their BL. Larvae detached from the substrate on day 4 began swimming and immediately displayed biting behavior on the body surface of the parents. Larvae had completely consumed their yolksacs by day 7. They began swimming at an earlier developmental stage compared with other cichlid species. Their thick lips may be advantageous for removing mucus from the bodies of the parent fish. Juveniles actively fed on Artemia spp. by day 30, and the frequency of biting behavior toward the parents decreased between days 20 and 35. Bone ossification was essentially complete in juveniles by day 32. Juveniles reached 16.0 ± 1.1 mm BL by day 35. These results indicate that the morphology and behavior of larval and early juvenile S. aequifasciatus exhibit adaptations for mucus provisioning.

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