Reproduction and growth of the freshwater shrimp, Paratya compressa improvisa in the Tsurugata Marsh [Japan] Akita prefecture
2006
Imai, T.(Yurihonjo City Iwaki General Branch Office, Akita (Japan))
The present study deals with reproduction and growth of the shrimp, Paratya compressa improvisa, a land-locked subspecies, in the Tsurugata Marsh, Akita Prefecture. This study was based on specimens at all the developmental stages from larvae through mature adults collected semimonthly during the period of two years between May, 2001 and June, 2003. Ovigerous females appeared from April or May to September. Among them, those taken during April through July were large-sized individuals which were born in the preceding year, while those taken in August and September comprised of small-sized individuals (0-age) spawned in June. Juveniles, about 5 mm in body length, were found during June through early September, the peak being in June and July. They were derived from adults that were born in the previous year. Even though young females started reproduction in the summer, only a few of the juveniles from them were collected in and after late September. The juveniles settled in June grew fast in summer and early autumn, and males and females reached 14.5 mm and 15.9 mm in body length, respectively in October. After retardation of growth in winter months and even apparent reduction of mean body length in March and April, the shrimps started to grow with the rise of the temperature, reached up to 16.4 mm for males and 20.0 mm for females by June, the major reproduction season. The growth curve after settlement defining June 9 as the starting point was expressed as Lt=20.351(1-exp(-1.466 (t/365+0.372)+(0.222/2pi) sin (2pi(t/365-1.694)))) for males and Lt=29.683(1-exp(-1.030(t/365+0.275)+(0.123/2pi) sin (2pi(t/365-1.652)))) for females, where Lt is the body length in mm at age t in days after settlement. The shrimps finished their life span after reproduction.
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