**1. Introduction**

Across the ages, Man has been harnessing water resources to suit his needs whether for power generation or for food, fishing and aquaculture. The first aquaculture tryouts started more than 4000 years ago in Egypt with the production of the famous fish: Tilapia [1]. Till to date, tilapia has remained an important food resource, in the family Cichlidae, with two species being predominantly cultivated: Mozambique Tilapia (*Oreochromis mosambicus*) and Nile Tilapia (*O. niloticus*), which alone

accounts for more than 1/5 of the total global aquaculture production; and 85% of tilapia production [1–4]. Nile tilapia, a species native to the Nile River, also inhabits the Niger, Volta, and Senegal River Basins [1, 5, 6]. Thanks to its suitability for aquaculture and given its quick adjustment to extreme and varied environments, its ease of reproduction in captivity and its wide ecological valence, this fish has been the subject of various breeding attempts and has been widely spread in all continents since the 1960s [7, 8].

Around the world, several methods have been used to breed tilapia, including extensive (mostly in ponds), semi-intensive, intensive and mostly hyper-intensive systems. These methods are characterized by the use of selected strains and a highperformance compound feed [4, 9]. Nile Tilapia is widely known for its adaptability to different farming systems linked to its spawning period which spreads over the whole year. Likewise, this species is known for its resistance to pathogens as well as its ability to withstand stressful environments and the different manipulations associated with aquaculture [10].

In addition to the afore-mentioned advantages, *O. niloticus* has an intriguing growth rate, unique when compared to other species of the cichlid family. On top of a good food conversion ratio associated with an excellent ability to accept artificial feed [11–13], its diet corresponds to the lowest levels of the food chain (phytoplankton, detritus...). All these attributes make the production costs of this species relatively moderate and adequate. In Tunisia, in addition to mullet, pikeperch and carp, the rearing of *O. niloticus* could prove to be an interesting future alternative for the partial replacement of the production of other freshwater fish, given its very remarkable biological characteristics in inland fish farming.

Tilapia was first introduced in 1966 in Kebilli Oases, where aquaculture is often connected with agricultural practices, taking advantage of the warm climate and the abundant geothermal water resources in southern Tunisia. However, despite the unerring documentation of Tilipia's survival and reproduction [14], it was not until 1999, that the idea of breeding this species was pursued. This took place after the experimental research station in geothermal pisciculture of Bechima in the governorate of Gabes was founded by the National Institute of Sciences and Technologies of the Sea (NISTS). Since then, several experiments have reported effective management and success of the different rearing cycles of this species, from spawning to grow-out [15]. In parallel, various acclimatization experiments of tilapia have been conducted in the southern oases, as well as in the reservoirs in the north and center of Tunisia, where the low winter temperature hinders the growth and survival of this species. These experiments have shown encouraging results and breeding success especially at the reservoirs of Lebna, Lahma, Ghezala and Sidi Saâd [16, 17].

The present study was commissioned by the Technical Center of Aquaculture (TCA) and the Higher Institute of Fishery and Aquaculture of Bizerte (HIFAB), within the framework of a convention signed in 2015 between the TCA and the NISTS which aims to ensure the annual production of 300,000 single-sex male Nile tilapia fry. In other respects, the researchers sought to identify the most suitable environment for the rearing of this species in Tunisia through pinpointing the strengths and weaknesses associated with this species' farming in two quite different environments (fresh and geothermal waters). To achieve this goal, the physicochemical parameters of the study areas, zootechnical parameters of the fish and pathologies were considered on top of the monitoring and evaluation of the different rearing phases (hatching, larval rearing, and grow-out) and the economic study.
