REPRODUCTIVE BIOLOGY OF THE MYSTID A. trigibba, LITORAL ZONE,SOUTH SINALOA

Biology and reproduction of the mysid Amathimysis trigibba at the mouth of the Presidio River and mouth of the Urias estuary January 2010 - March 2012. Distribution was restricted to shallower stations and bottom level; abundance was highest between October and March. Mean total length was 2.76±0.27mm in ovigerous females and 3.04±0.36mm in males. Sex ratio (H:M) was 3.8:1. Fecundity ranged from 1 to 11 embryos/female with an average of 5.26+2.15. The most frequent number of embryos was 6. There was no correlation between the size of ovigerous females and fecundity. Four stages of marsupial development were identified. The average number of embryos was slightly higher in Stage 1 with 5.49±2.05 emb/female, non-significant differences in embryo number between early and late stages indicate low mortality throughout marsupial development (P>0.05). Mean size ranged from 0.37mm to 0.32mm for a fecundity of 1emb/female to a fecundity of 11 emb/female, differences were not statistically significant (P>0.05).