Simulated transport of flathead grey mullet Mugil cephalus eggs: Effects of density and duration

Abstract

Flathead grey mullet has a great potential as a low trophic level aquaculture species, however captive rearing is still hampered by the lack of well-established production protocols. Here we examined the effects of transport time and egg loading density on water quality, egg survival, hatching success and early larvae performance when shipped for 8, 16 and 24 h at 500 and 1500 eggs L−1. When no water conditioners were used, survival immediately after transport was consistently over 60% up to 16 h shipment for both densities tested, with minimum values of 40% for 1500 eggs L−1. Density and transport time did not influence hatching rate (p > .05) which ranged between 31 and 54% after 8 and 16 hour transport. However, manipulation after 8 and 24 h transport led to a significant drop in early larvae survival regardless the density tested (20% and 5% respectively) compared to 16 h transport (40%) (p < .05). Hence, the results indicate that grey mullet is sensitive when manipulated as early hatched larvae and when eggs undergo blastophore closure at circa 20 h post-fertilization.The tested egg stocking densities do not deteriorate water quality to lethal levels in terms of pH, NO2 and NO3 especially for short and medium transportation times, however, 24 h transportation induces an accumulation of ammonia affecting the long-term survival of larvae. When basic technology is available (i.e. no water conditioners, refrigerated vehicles), we suggest manipulating grey mullet eggs at 28 h post fertilization for best results in terms of hatching rate and early larvae survival.