Ferdous Ahamed

Growth Patterns and Longevity of the Pandalid Shrimp Plesionika izumiae (Decapoda: Caridea)

ABSTRACT The pandalid Plesionika izumiae Omori, 1971 is widely distributed in the west Pacific regions. This is a relatively common shrimp in the coastal waters of Japan, except off northern Honshu and Hokkaido, and is commercially important for small-scale bottom seine fishery. The growth patterns and longevity of P. izumiae were estimated in Kagoshima Bay, southern Japan, using time series of the length-frequency distributions during February 2007 to January 2011. Carapace length ranged from 4.4–14.5 mm in males and 4.0–14.7 mm in females. Both males and females were first recruited in autumn (October—November) with modal size around 7.0 mm carapace length. The growth was best described by the Pauly and Gaschütz equation as Lt = 11.95[1 - exp{-3.991(t/12 - 0.118) - (2.866/2&pgr;) sin(2&pgr;(t/12 - 0.955))}] for males and Lt = 12.73[1 - exp{-4.084(t/12 - 0.142) - (2.646/2&pgr;) sin(2&pgr;(t/12 - 0.912))}] for females. Females grew faster and reached a larger size at the same age than males. Monthly growth rate was lower during December to February and higher during March to May in both sexes. The longevity of this species was estimated to be around 18 months for both sexes. The relationship between carapace length and body weight indicated negative allometric growth in males and positive allometric growth in females.

Reproductive Biology of the Pandalid Shrimp Plesionika izumiae (Decapoda: Caridea)

Abstract The pandalid shrimp Plesionika izumiae is a relatively common shrimp in the coastal waters of Japan, except off northern Honshu and Hokkaido. This is one of the dominant species in the benthic community of Kagoshima Bay, southern Japan. The reproductive biology including, reproductive period, size at sexual maturity, embryo size and brood size of P. izumiae was studied in the bay. All females were examined for the presence of embryos attached to the pleopods and the developing embryos were classified into four stages. Ovarian development was also observed based on morphological observation. Ovigerous females occurred throughout the year with higher percentage during May to November, indicating this was the main reproductive period. Ovarian maturation was observed during the incubation process of embryos, suggesting that females were potentially capable of multiple spawning during a reproductive period. The size at sexual maturity was estimated to be 8.5 mm in carapace length based on the method using the size at which 50% of the females were ovigerous. Embryo size was independent of the body size (carapace length) of females but increased with development. There was a positive correlation between brood size and body size, while a significant reduction of embryos was observed during the course of development.