Postembryonic growth, development and reproduction of Gammarus aequicauda (Martynov, 1931) in laboratory culture

Gammarus aequicauda (Martynov, 1931) is an epibenthic amphipod very well adapted to life in estuaries and shallow coastal waters. In Mar Piccolo in Taranto it is the most abundant macrofaunal species on soft bottom communities. The life history of G. aequicauda was analysed in laboratory culture under controlled conditions of 18°C and salinity of 36 in order to assess postembryonic growth, development and reproduction. Pairs of amphipods in precopula were observed daily until the female was found to be ovigerous. The fecundity was estimated as the number of juveniles released by each female. Juveniles produced in the laboratory were transferred to new aquaria and at an interval time of 7 days, the head length was measured, the antennal segments were counted and the sexual maturation stage was assessed. The mean time spent in precopula ranged from 1-3 days and embryonic development ranged from 5 to 8 days. The head length of newly born G. aequicauda was approximately 0.23 mm in head length (0.1 mg dry weight) and the heads reached a maximum length of about 1.8 mm (11.85 mg) after 140 days. There was a significant correlation between head length and number of articles (1st antennae). A positive correlation between the number of juveniles and the size of G. aequicauda females (as head length) was also observed. The females produced at least three broods consecutively with a mean offspring number of 19.3±13.3. Male were on average larger than females. The sex of males could be determined at an age of 30-37 days and the first precopula was found after 40 days. Increase in egg volume, during development, was not significant (p>0.05). Growth continued throughout life under laboratory conditions. One important feature of this study was to provide the essential basis for the development of laboratory toxicity tests with cultured animals. There are several advantages using laboratory cultured populations: the individuals are close to the normal physiological state and they are capable of growing and reproducing in captivity; the animals are of known ages and are available throughout the year.