Bizerte lagoon is a valuable socio-economic ecosystem which is renowned for its significant biodiversity and its strategic position in the Mediterranean and in northern Tunisia. It is characterized by an important biodiversity and a high biological productivity, which makes of it a nursery for several marine species. It is also a place of brood stock maturation for others and a feeding area for many migratory species. Its shores and maritime space host lots of human activities, such as coastal fishing, shellfish farming, maritime traffic, recreational fishing and nautical sports, besides 277 industries spanning several sectors of activity such as leather and textile as well as the refining of hydrocarbons and the steel industry. These activities cause severe pollution and result in many anthropogenic disturbances. The aim of this work is to study the sanitary state of Bizerte Lagoon using a biological and ecosystem approach that exploits bio-ecological indicators at the scale of specimen, population, community or whole ecosystem. The findings of this study have revealed the following facts: the peri-lagoon part of the Northeast zone is distinguished by an interesting biological diversity. According to statistical descriptors, the most abundant and frequent zoological groups are gastropod mollusks followed by crustaceans. In terms of diversity indexes, the values obtained showed that the Northeast zone has a poor to mediocre ecological status. This research demonstrates that Bizerte Lagoon is undergoing an anthropic pressure that has been jeopardizing the biodiversity of this ecosystem.

In this study, we present the technical characteristics and the methods applied for fashioning different types of cages used in the aquaculture of Nile tilapia. This study was based on experiments made in geothermal water and fresh water reservoirs in Tunisia. The structures showed high efficiency in small-scale freshwater fish farming. The results of the growth of tilapia fry, reared in the two areas, showed a wide variation. However, with regards to cages’ effect on its behavior and growth rate, a negligible influence was noted. In fact, after the pre-growth phase of the fry in cages in geothermal waters during 35 days, we obtained a daily growth rate (DGR) of 0.41g/day and a specific growth rate of 7.11%/day. These changes are superior to those found in freshwater cages whose DGR was around 0.18g/day and specific growth rate (5.98%/day). Besides, the grow-out trials carried out in the SidiSaad, Ghezala and Lahma Reservoirs have given encouraging results with respective densities of 75 P/m3, 77 P/m3 and 61 P/m3. The use of 2m3 and 3m3 cages, which are relatively of low cost, showed high efficiency during their handling, such as good shape retention in water and especially low mesh clogging. According to the results of the present study, it is recommend the use of cages with a volume of 50m3 above the water surface in order to prevent fish jumping out of the cage, also the assembly of the cages for pre-growth and the grow-out must be carried out within the same reservoir in order to minimize the production costs.