Reproductive biology of Argis lar from the East Sea of Korea (Decapoda, Natantia)

We studied the reproductive biology of Argis lar from the East Sea of Korea, based on a total sample of 4172 shrimp collected over a 12 month period. The sample included 40 males (size range: 9.91-24.11 mm carapace length, CL), 2797 non-ovigerous females (size range: 7.22-38.33 mm CL), and 1335 ovigerous females (size range: 19.70-37.43 mm CL); size differed significantly among the three groups. Ovigerous females occurred during every month of the year, in varying percentages, with a minimum abundance of 2.48% in August; the extended reproductive period indicates that multiple spawnings occur during the year. All ovarian stages were present in non-ovigerous females, whereas only spent ovarian stages were present in ovigerous females. Two modes were present in the abundances of females at each ovarian stage. In the first mode, females at the mature ovarian stage were most abundant in September (61.98%) and females in the spent ovarian stage were most abundant in November (32.52%). In the second mode, females at the ripe ovarian stage were most abundant in December (62.96%) and females at the spent ovarian stage were most abundant in March (66.00%). The gonadosomatic indices of non-ovigerous females and ovigerous females varied significantly by month. The percentages of ovigerous females with eggs at different stages of development were: non-eyed eggs, 32.06%; eyed eggs, 25.69%; and hatching eggs, 42.05%. Females with hatching eggs occurred from November to June. The relationships between CL and ovary weight differed significantly between ovigerous females with eggs in the non-eyed and eyed stages. Our results indicate that the highest indices of reproductive potential (IRP) occurred in females in the 29.1-31.0 mm CL size class (IRP = 405).

Pair formation in Spongicola japonica (Crustacea: Stenopodidea: Spongicolidae), a shrimp associated with deep-sea hexactinellid sponges

The population structure of the deep-sea sponge-associated shrimp Spongicola japonica was investigated, and the mechanism of pair formation analysed from field samples. The composition pattern of shrimp in host sponges was divided into three patterns by sex and number as follows: solitary, a solitary inhabitant; sexually paired, a pair with a male and a female; grouped, multiple individuals excluding those designated as sexually paired. Juveniles usually remained grouped or solitary in a host cavity until the size at which gonadal maturity starts. Before forming sexual pairs, shrimp appear to have a free-living period outside the host, when the ovarian stages of females correspond to early to late vitellogenesis. Re-invasion is just before the first spawning, when females are in the ovarian stage of late vitellogenesis.

Intermolt Insemination, an Alternative Mating Strategy for the American Lobster (Homarus americanus)

American lobster (Homarus americanus) have a dual mating strategy. Although most females mate when they are newly molted, mating can occur at any molt stage if necessary, in the laboratory, virtually all uninseminated preovigerous females mate prior to spawning. Male aggression is a major factor in the success of intermolt mating and males can discriminate between immature and mature females, and between inseminated and uninseminated females. Female receptivity is affected by both ovarian stage and the presence of stored sperm, but not by molt stage. Most females become unreceptive after insemination, but their receptivity returns once the supply of stored sperm is exhausted. Intermolt mating occurs in smaller lobster that for some reason did not mate at molt, and it is an important part of the reproductive strategy of larger lobster. Lobster s[Formula: see text] carapace length frequently spawn twice without molting and often fail to store sufficient sperm to fertilize consecutive spawnings. Intermolt mating ensures these females will produce fertile second broods.

Reproductive biology and growth of the Western School Prown, Metapenaeus dalli, in a large Western Australian Estuary

During the summer, one-year-old western school prawns (Metapenaeus dalli) congregate and spawn in reduced-salinity (< 10 g kg-1) regions of the Murray River, a tributary of the large Peel-Harvey estuarine system in Western Australia. Although some 1 + prawns are found into the following spring, few if any survive or remain in the system until the next spawning season. Growth is highly seasonal and females attain a greater carapace length than males by the end of the first year of life (18 v. 14 mm). Changes in the incidence of spermatophore deposition, gonadosomatic index (GSI) and ovarian stage during the spawning period are described. Although the timing of recruitment of O+ prawns could be related to the sharp peak in the incidence of spermatophore deposition and GSI in 1985-86, such relationships were not so clearly defined in 1987-88 when the incidence of spermatophore deposition remained above 9% for over twice the length of time.