BIOLOGICAL CHARACTERISTICS OF MYSID NEOMYSIS MIRABILIS IN DEPENDENCE ON ITS ENVIRONMENTS (PETER THE GREAT BAY, JAPAN SEA)

Abstract

Size and sex structure of mysid Neomysis mirabilis in Peter the Great Bay is studied. The net samples (160 and 260 per year) were collected at the depth of 0.5–2.0 m in the southern external part of the secondary Amur Bay (at Popov and Reineke Islands) and in its northern internal part, over the total area of approximately 3 km2, in the daytime in May-September from 2014 to 2017. The catch was recalculated per 1 m3of water. The water temperature was measured and weather conditions were recorded. All mysids (2926 ind.) were measured under binocular microscope with accuracy of 0.1 mm, weighted by torsion scales with accuracy of 1 mg, and separated to males, females and juveniles. The females were differentiated by 5 stages of development: 1) immature females with oostegetic rudiments, 2) oviparous females, 3) females with embryos in the marsupia bags without stalk-eyed with black pigment, 4) females with embryos in marsupia bags with black eyes, 5) spawned females with empty marsupii. The females prevailed: 71.3–97.0 % in the southern Amur Bay and 39.0–56.7 % in the northern Amur Bay, while the portion of males was 2.2–28.7 % and 20.9–43.3 %, accordingly. The body length varied from 3.0 to 23.5 mm; the females and males had the same sizes, on average 14.5–15.4 mm in the southern Amur Bay and 8.3–11.2 mm in the northern Amur Bay, with slight decreasing from spring to summer. The spawning was extended in time because of several generations changing. Mysid females with eggs, their embryos at different stages of development, and juveniles of different size were presented permanently. Aggregations of N. mirabilis formed for a short time starting in middle April — middle July in the southern Amur Bay and in middle May — late July in the northern Amur Bay. The mysid biomass in the aggregations was 3–5 g/m2 and 10–500 g/m2in these areas, respectively, that is appropriate for the commercial fishery. Spatial difference of the mysid biological parameters and abundance is explained by different environmental conditions in the internal and external areas of the Amur Bay.