Reproduction and rearing of the flathead grey mullet Mugil cephalus (Linneus, 1758) and of the sea urchin Paracentrotus lividus (Lamark, 1816) for restocking purposes
Author(s)
Vallainc, Dario
Date Issued
June 15, 2017
Type
Doctoral Thesis
Abstract
Grey mullet Mugil cephalus and sea urchin Paracentrotus lividus roe are well-known and appreciated products. A decline in wild population of both species and a growing demand promote new interest in the use of cultured individuals to help replenish depleted stocks.
The research activity of this thesis was mainly devoted to concurrently defining protocols for spawning, hatching and rearing the two species for restocking purposes.
Some of the results obtained at a laboratory scale for sea urchins produced the following results: (i) an optimisation of the larval rearing protocol; (ii) the identification of an optimal larval diet; and (iii) the use of Ulvella lens as metamorphosis-inducing factor in competent larvae. The experimental trials from laboratory to pilot scale comprised the use of rearing protocols and diet developed in volumes from low to high(from 5 to 300 L), in order to study the effect of stocking densities on larval survival and development. Results were encouraging. There was a reduction in water exchange, a similar phytoplankton consumption, an expected lower but satisfactory survival (13% vs 80%) and similar competence (~30%).
For the spawning in captivity of M. cephalus we successfully induced gametes emission in three reproductive cycles with the production of more than 300,000 larvae. Three different rearing densities were compared and an inverse correlation of growth with density was observed for both larvae and juveniles. Average biomass production in the 3 cycles ranged from 0.4 to 1.4 g/L, with the production of 1,000 to 4,700 individuals. The condition index was ~ 3 for all cycles, indicating that the M. cephalus juveniles produced had been correctly reared. A comparison between two different rearing methods, one 100% indoor and another 50% indoor and 50% outdoor, showed quite similar growth performances (~0.24 mm/day), indicating that the release of the fry in pre-adaptation cages into a lagoon at about 3 cm could be a good practice in terms of sustainability of the process.
Additional information
Dottorato di ricerca in Ecologia e gestione sostenibile delle risorse ambientali
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