Occurrence of Pacific bluefin tuna Thunnus orientalis larvae off the Pacific coast of Tohoku area,northeastern Japan: Possibility of the discovery of the third spawning ground

Recently, based on the histological studies it is suggested that Pacific bluefin tuna (PBF) spawns in the Kuroshio–Oyashio transition, off the Pacific coast of northeastern Japan, in addition to the previously identified two spawning areas of the northwestern Pacific around the Nansei Islands and the Sea of Japan. Distributional surveys for PBF larvae have not been conducted in the Kuroshio–Oyashio transition, and thus, we conducted PBF larval surveys at twenty stations in this area in early August 2018 to obtain evidence for the spawning of PBF. Twelve PBF larvae (3.9–7.2 mm in body length) were collected at six stations where sea surface temperature ranged from 27.2 to 28.2°C. Otolith microstructure analysis indicated that age of these larvae ranged from 4 to 11 days after hatching and the larvae hatched in late July. Growth of the collected larvae was comparable to those in the other two spawning grounds. Therefore, PBF spawns, hatches, and at least survives to the postflexion stage, 11 days after hatching in the Kuroshio–Oyashio transition. This fact potentially has a large impact on recruitment processes of PBF if they survive to recruitment in this third spawning ground.     

Evaluation of recycled food waste as a partial replacement of fishmeal in diets for the initial feeding of Nile tilapia Oreochromis niloticus

A 70-day feeding trial was conducted to evaluate the suitability of recycled food wastes [food industry waste (FIW) and soy sauce waste (SSW)] as protein sources in the diet of Oreochromis niloticus fry. Diets were formulated that contained 0 and 20–22%, respectively, recycled food wastes, namely D1 (0% recycled food waste), D2 (20% FIW), D3 (10% FIW and SSW, respectively), D4 (20% FIW and tryptophan), and D5 (22% SSW). Although feed efficiency, net protein retention, and protein efficiency were not significantly different among fish on the different diets (p > 0.05), those on D3 had a better growth performance than the controls (D1). Fish fed diet D4 (tryptophan supplement) had a higher final weight gain than those fed D2, in addition to the other growth parameters, but these differences were not significant (p > 0.05), with the exception of total feed intake. D1 produced fish with higher carcass protein, while fish fed on D3 had the highest lipid content. There was no significant difference between groups in terms of carcass moisture and ash contents. These findings show that the proper combination of recycled food waste is suitable for use in the production of fish feed and may ultimately result in reductions in the level of fishmeal in aquafeeds.     

Otolith development and daily increment formation in laboratory-reared larval and juvenile black-spot tuskfish <Emphasis Type="Italic">Choerodon schoenleinii</Emphasis>

Microstructures of lapilli were examined for reared larvae and juveniles of black-spot tuskfish Choerodon schoenleinii. Lapilli of larvae at 1 day after hatching have one diffuse and obscure ring with an otolith radius of 4.3 ± 0.50 μm (mean ± SD, N = 8). The slope and intercept of the regression between the number of days after hatching and increment counts did not differ significantly from one and zero, respectively, indicating that lapillus increments were formed on a daily basis after hatching. There was an ontogenetic shift in the relative values of somatic and otolith growth, which corresponded to the transition from pelagic larvae to settlement stage. Simultaneously, the daily increment width reached the maximum value. These findings suggest that age at maximum value of increment width can be used as an indicator of the planktonic larval duration while settlement mark is not found. Since ontogenetic shift in the relationship between otolith radius and body size was observed, back-calculation of somatic growth in black-spot tuskfish using the otolith radius during the early life stages should be analyzed with caution, and the method requires further validation.     

Site fidelity,size, and spatial arrangement of daytime home range of thumbprint emperor <Emphasis Type="Italic">Lethrinus harak</Emphasis> (Lethrinidae)

Although emperors (Lethrinidae) are commercially important fisheries resources in tropical and subtropical waters, their home range size and its spatial arrangement have not been sufficiently clarified. In the present study, the size and spatial arrangement of the daytime home range of the thumbprint emperor Lethrinus harak were investigated by using a portable GPS receiver. In a 150 m × 200 m quadrat, 21 individuals of the species were identified by their color pattern, and individuals were divided into four arbitrary size classes (class 1 < 20 cm TL ≤ class 2 < 25 cm TL ≤ class 3 < 30 cm TL ≤ class 4). Fish tracking by snorkeling was conducted with the portable GPS receiver. Daytime site fidelity of this species was high and there was a significant positive correlation between the home range size and fish total length. Home ranges of same-sized individuals abutted each other (20.3% area overlap), whereas those of different-sized individuals overlapped (48.3% area overlap). Agonistic behavior (attacking) occurred significantly more frequently between same-sized individuals than between different-sized individuals. These results suggest that daytime home ranges of Lethrinus harak can be regarded as territories against same-sized individuals, but not different-sized individuals.     

Detection of Bemisia tabaci Mediterranean cryptic species on soybean in São Paulo and Paraná States (Brazil) and interaction of cowpea mild mottle virus with whiteflies

Since the detection of Bemisia tabaci Middle East-Asia Minor 1 (MEAM1) species in Brazil in the early 1990s, this whitefly has been the predominant species and the main viral vector in the country. In this work, whiteflies were collected from commercial soybean fields near and far from greenhouses where Mediterranean (MED) species had previously been detected infesting vegetable crops. Results indicated that MEAM1 was the predominant whitefly species in soybean in most sampling sites, while MED was found colonizing soybean plants in open field conditions alone and/or with MEAM1 in several places. Among the tested insects, MED species was mostly detected harbouring the facultative endosymbiont Hamiltonella. We also detected cowpea mild mottle virus (CPMMV) infecting soybean plants. Transmission assays demonstrated that MED species was more efficient transmitting CPMMV from beans to beans and from soybean to soybean plants than MEAM1, while MEAM1 was more efficient in transmitting the virus from soybean to bean than MED. Performance assays indicated that adult emergence of both species on CPMMV-infected soybean plants was higher when compared with the emergence on healthy plants. Moreover, nonviruliferous MED and MEAM1 adults preferred to settle more often on healthy plants, while viruliferous adults settled more often on CPMMV-infected soybean plants. As MED has already been found in soybean open fields in São Paulo and Paraná States, Brazil, and it is a good vector of CPMMV, we anticipate problems related to whitefly management and to increase in the incidence of the virus in soybean.