Relative growth and sexual maturity of the pandalid shrimp Plesionika izumiae (Decapoda, Caridea) in Kagoshima Bay, southern Japan

Abstract

The pandalid shrimp Plesionika izumiae Omori, 1971 is widely distributed in the west Pacific region. This is a relatively common shrimp in the coastal waters of Japan, except off northern Honshu and Hokkaido, and it is commercially important for small-scale bottom seine fishery. The relative growth of secondary sexual characters (appendix masculina for the male and abdomen width for the female) of P. izumiae was studied in Kagoshima Bay, southern Japan, from December 2009 to November 2011. The length of the appendix masculina was measured for males, while abdomen width near the second pleopod was measured for females. The relationships between carapace length and the observed secondary sexual characters were studied using the least squares method. The appendix masculina showed positive allometric growth in relation to carapace length (CL), showing discontinuities at 7.3 mm CL. The width of the female abdomen showed positive allometric growth with CL, while indicating a discontinuity at 8.6 mm carapace length. The observed discontinuities in the growth rate of secondary sexual characters of P. izumiae might be attributed to sexual maturation.