טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentZivan Amir
SubjectDevelopment of a Cost Effective and Environmental Method for
Commercial Breeding of Mullet Fish
(Mugil Cephalus) in Low-Salinity, Low-
Hardness Waters
DepartmentDepartment of Civil and Environmental Engineering
Supervisor Professor Ori Lahav
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Abstract

Gray Mullet (Mugil cephalus) is a Mediterranean fish species which lay their eggs in the sea. The fingerlings enter into deltas of rivers and are caught in fishermen’s nets for rearing in aquaculture fish ponds.

Attempts at growing the fish in the Dan stream water have encountered several difficulties, such as massive mortality of fingerlings due to adaptation problems to this relatively low-salinity water, following their transport from fish farms along the coast. The reason for the apparent physiological stress and high mortality has been ascribed to the low salts concentration.

The research hypothesis was that it would be possible to grow the fish in a cost effective fashion by supplying the minerals required to the fingerlings during the acclimation period by dissolution of cheap calcite and dolomite rocks from local quarries.

Calcite and dolomite dissolution was performed in the study with predetermined concentration of acid using a packed bed column. It was found that the upflow velocity had a significant effect on the dissolution rate; increasing the velocity assisted in evacuation of dissolution reaction products from the solid-aqueous contact surface and into the solution bulk. Moreover, the results showed that one can predict the dissolution potential in the effluent, based on the DP in the influent to the reactor and the applied hydraulic retention time.

In the second part of the work fingerlings were reared in different water characteristics in order to assess survival and growth rates. The results showed that habituating the fingerlings in the Dan water is inapplicable due to high mortality rates (65% mortality). However, habituating the fingerlings in brackish groundwater, diluted brackish groundwater water, artificially produced solution or dolomite dissolution water yielded a high survival rate (78%-85% survival). Habituating the fingerlings in the dolomite dissolution water appears to be the preferred economic solution.

This work also included the development of a computer MATLAB-based algorithm, whose purpose was to design a simple dissolution process of calcite and dolomite by packed-bed reactors.

It was found that the costs of increasing calcium and magnesium concentrations in Dan stream water to the aforementioned values were approximately 1.8% of the overall cost of producing 1 kg of fish.

The results presented in this work prove that the rationale of using dolomite/calcite dissolution reactors as a source for calcium and magnesium addition to soft waters is feasible to answer the difficulties encountered in rearing Mullet fish in low salinity waters.