Reproductive biology of the freshwater shrimp Macrobrachium tenellum (Smith, 1871) (Decapoda: Caridea: Palaemonidae) in Mexico.

We analyzed the reproductive cycle of females of the palaemonid shrimp Macrobrachium tenellum (Smith, 1871) collected in the Ameca River, between the Jalisco and Nayarit states, Mexico. We studied the seasonal occurrence of ovigerous females during the year, their relationship with abiotic factors, and the size of the first sexual maturity. The study included 7,100 specimens of M. tenellum , of which 2,791 (39.3%) were males, 3,559 (50.1%) females, and 750 undifferentiated (10.6%). The sex ratio of the total (male-female) population differed significantly from the expected 1:1 with more females. A total of 309 females carried eggs (8.7% of all collected females). Ovigerous females, which were collected in three of the four sampling sites, were found almost year-round (with the exception of March and December), and their number showed a significant positive correlation with water temperature and rainfall. The size of first maturity (TL _50% ) for all collected females was 55.7 mm total length (TL), ranging from 64.3 mm TL to 42.7 mm TL. The results revealed that the population of M. tenellum in the Ameca River has a continuous reproductive period associated with the rainy season and increasing water temperature. [ABSTRACT FROM AUTHOR]