FIRST EXPERIENCE OF CAGE CULTIVATION OF HATCHERY-PRODUCED JUVENILE SCALLOP MIZUHOPECTEN YESSOENSIS AT EASTERN COAST OF PRIMORYE

Yesso scallop Mizuhopecten yessoensis is the main object of aquaculture in Primorye with annual yield measured in hundreds ton. However, further development of its farming could be restricted by lack of the spat. Availability of the spat imported from China using for the scallop cultivation at the coast of Primorye is explored. The spat from Chinese hatchery located in Shandong province was supplied for one aquaculture company in Primorye in the volume of 660 . 106 ind. in 2018 and settled to hanging collectors (1000 ind. per bag), then to cages in the marine farm located north-eastward from the Moryak-Rybolov Bay. Survival and growth rate of the scallop juveniles were examined in early November 2018, when the water temperature was from 10.3–10.4 оС at the sea surface to 9.7–9.9 оС at the bottom, salinity was about 33.60 psu in the whole water column, chlorophyll a concentration varied in the range 0.4–0.8 mg/L with the maximum in the layer 8–24 m. The spat mortality during transportation was estimated as 15 %, but it increased to 56–90 % during its growing up in cages. This level of mortality is much higher than mortality of the spat collected from the coastal waters at southern Primorye. The highest mortality of artificial spat was observed for large-sized mollusks, whereas it was satisfactory for the small-sized ones. Possible reason of high mortality is too high density of juveniles and damaging of their soft tissues by other shells. The spat shells height did not exceed 5–10 mm in the collectors but increased during their growing in cages to 20–25 mm. This size is similar to the size of scallop growing from natural spat in southern Primorye. However, growth rate of the scallop growing at the Moryak-Rybolov Bay (2.0–2.7 mm/month) is lower than in Peter the Great Bay (3.0–3.5 mm/month) though higher than in the Vladimir Bay and Aniva Bay. Mean body weight of the cultivated scallop in November was 1.5 ± 0.1 g.

Efficiency of scallop Mizuhopecten yessoensis cultivation in the Ussuri Bay (Japan Sea)

Data on cultivation of scallop Mizuhopecten yessoensis in the Ussuri Bay are generalized. The marine farms are located in the shallow waters at depths of 2-18 m, their plantations occupy different areas with different hydrodynamics. Complex structure of the plantations (collectors, cages and bottom facilities) is formed in the semi-closed Sukhodol Bay, but bottom plantations only for growing of scallop and sea cucumber are mounted in two other bays. The local broodstocks of scallop were formed by juveniles transported from the Posyet Bay, after that at least 20 million individuals of scallop spat were collected in three bays in 2000-2014, and their growing gave the total commercial output about 216 t (111 t in the Sukhodol Bay, 70 t in the Ilmovaya Bay, and 35 t in the Malye Kushi Bay). This is rather weak result that shows that the area has limited abilities for development of this type of aquaculture. The main reason was low density of spat on substrata: it never exceeded 200 ind./collector and did not increase during the farms development, so the farmers were forced to increase the number of collectors to obtain required number of spat; moreover, some years were unfavorable for collecting of juvenile scallops. There is concluded that environmental conditions in the eastern Ussuri Bay are not optimal for the scallop cultivation by extensive method.

Comparative study of the composition and genetic diversity of the picoeukaryote community in a Chinese aquaculture area and an open sea area

Picoeukaryotes (<2–3 μm) perform key roles for the functioning of marine ecosystems, but little is known regarding the composition and diversity of picoeukaryotes in aquaculture areas. In this study, the Illumina MiSeq platform was used for sequencing the V4 variable region within the 18S rDNA gene to analyse genetic diversity and relative abundance of picoeukaryotic communities in the Qinhuangdao scallop cultivation area of the Bohai Sea. The community was dominated by three super groups, the alveolates (54%), stramenopiles (41%) and chlorophytes (3%), and three groups, dinoflagellates (54%), pelagomonadales (40%) and prasinophytes (3%). Furthermore, a contrasting station with open water away from the eutrophic aquaculture area was chosen. The communities collected from the two stations exhibited significant differences, with higher diversity in the aquaculture area. These results provide the first snapshot of the picoeukaryotic diversity in surface waters of the Qinhuangdao scallop cultivation area, and basic data for future studies on picoeukaryote community in an aquaculture region.