A growth model for a hyalid amphipod Hyale perieri in the coastal water of Alexandria (Egypt)

The growth rate of the hyalid amphipod Hyale perieri was studied on the bases of Ikeda's growth model which is based on the inter moult period (IP) and moult increarment (△BL). To apply this approach, laboratory experiments were carried out at three temperatures regimes (15℃, 20℃, 25℃) to gain accurate data of IP and BL. The total number of specimens used in this study was 86 at 15℃, 24 at 20℃ and 70 at 25℃. The number of flagellar segments of both antennae of the Hyale perieri could not be used as an index of growth (instar criterion). The obtained results indicated that, the predicted IP of the specimens was inversely related to temperature and in good agreement with the observed values at the experimental temperatures. IP data obtained from laboratory-reared specimes are combined with △BL data to establish a growth model for Hyale perieri from its release from the marsupium (1.64 mm BL) to the maximum size (12.67 mm BL) as a function of temperature. The maximum numbers of consecutive moults recorded during the experiment were 13 moults (14 instar) at 15℃, 14 moults (15 instar) at 20℃ and 12 moults (13 instar) at 25℃. The predicted life span for BL=12.67 mm (moult 13) was 203.82 d at 15℃, for BL=11.75 mm (moult 14) was 138.94 d at 20℃ and forBL=8.65 mm (moult 12) was 75.40 d at 25℃ respectively, thus confirming that the life span of the species is inversely proportional to temperature. Within the experimental temperatures tested, the optimum temperature for the growth of the species was 20℃.