Life history traits of the grass shrimp Palaemonetes antennarius (Decapoda, Palaemonidae) in the delta of the Neretva River, Croatia

The life history of the freshwater shrimp Palaemonetes antennarius (H. Milne Edwards, 1837) was investigated from April 1993 to November 2002 at 13 sites in the delta of the Neretva River, Croatia. The sex ratio (males vs. females) was in favour of females throughout the study year ( × ¯ ± SD = 0.70 ± 0.12 ) . The breeding period lasts from April to August with a peak of 75% of the ovigerous female in June. The maximum number of eggs carried by ovigerous females was 73, and there was a positive significant linear correlation between fecundity (number of early embryonic stage eggs per female) and female body size (carapace length) ( R 2 = 0.6 9 8 , p < 0.0 1 ). The breeding period was longer in limnocrenes and lakes with oligohaline–limnic water than in other habitat types because the water is more rapidly warmed in spring and cooled more slowly in autumn in these habitats. Larvae were present from June to October, with a peak reaching 19.4% of the total population in June. The shrimps follow a synchronic univoltine life cycle with a short egg-laying period and a new summer generation. Their larvae, apparently having no ecological flexibility, did not appear in any environment with high oscillations of salinity.