Effects of cortisol treatment on the salinity tolerance of Persian sturgeon, Acipenser persicus Juveniles

The freshwater shrimp, Macrobrachium nipponense is an invasive species which has recently been reported in Anzali Wetland, Iran. It exhibited good tolerance and adaption in this wetland ecosystem. This study examined certain aspects of feeding of M. nipponense in three habitats of this wetland. Shrimps were randomly sampled from April 2016 to March 2017. The stomach contents were obtained from 367 specimens ranging in length from 4.2 cm to 6.9 cm. The empty stomach index (VI) showed that this shrimp was a voracious (0 ≤ VI < 20) species in all seasons expect winter, when 99% of the specimens had empty stomachs. Fourteen dietary items were categorized in the three habitats of the wetland, with phytoplankton, mollusks and detritus forms being the dominant food items in the western, central and eastern habitats respectively. The feeding precedence index (FP) revealed that the most abundant portion of food was subsidiary one (50 ≥ FP ≥ 10) and the highest proportions of subsidiary food were phytoplankton (24.5%), gastropods (34%) and detritus (29.11%) in the western, central and eastern habitats, respectively. Omnivorous feeding is one of the reasons for the success, high tolerance and adaptation of M. nipponense in the Anzali Wetland ecosystem.