Production on the site is based on the intensive aquaculture of seabass (D. labrax) and seabream (S. aurata), with the additional option of producing tilapia (0. mossambicus). The first two species are identified in the appraisal report as being suitable for the local environment, indigenous to the Mediterranean, and in the cases of seabass, immediately suitable for intensive culture. Seabream have also demonstrated promising potential in intensive culture more recently, and may be considered for this role in addition to their use in semi-intensive production as suggested earlier. Tilapia, though not specifically identified in the appraisal report, may also be considered, particularly as a target for initial production, as although possibly less attractive in market terms, their simple and proven hatchery technology, ease and flexibility of culture, make them useful for meeting initial production goals. As will be shown later, there may also be some value in producing tilapia outside the main seasons for seabass and seabream.
Production cycles of both the two marine species are still strongly seasonal, (Fig. 4); although some progress is being made towards using photoperiod and temperature control to stimulate out-of-season spawninq, normal seasonal patterns can be expected to dominate commercial production schedules for some time. For tilapia, there would theoretically be the potential for spawning throughout much of the year, depending only on the temperature. However, spawning would more readily be achieved in fresh or brackish water, perhaps from a source outside the site - this factor may well in fact determine actual availability.
Hatchery production on site is based on that of the marine species; seabass and seabream, which can be considered to use similar facilities, with similar overall environmental and other requirements. The main cycles of production are shown in Table 2, which also outlines the main sequence of events, stages of production, and numerical requirements for an initial target of 50 t production. The effects of optimizing production techniques are also shown.
Details of feed requirements for hatchery stock are given in fig. 5. These are based on a standard algae/rotifer/artemia feeding system in initial stages., moving to artificial fry diets once the stock is weaned.
Metabolic stock requirements for a typical seabass stock cycle are shown in Fig. 6. These demonstrate the significant rise in biomass, whose increasing metabolic demands are partly compensated by the reduced requirements per kg as stock size increases and by the effects of lower temperatures-during winter months. Sea-bream are expected to demonstrate a similar pattern, while tilapia will show similar trends, but modified by the seasons through which specific crops are grown.
The consequences of these demands on water flow and holding capacity are shown in Fig. 6 and Tables 2 and 3. These show.a pronounced seasonal peak requirement mainly dominated by the 2-year old fish, during the Summer months. This will be modified in practice by the harvesting strategy. Harvesting decisions-will depend on market conditions, on the size ranges of fish acceptable to local consumers, (and on the size ranges of fish acceptable to local consumers), and on the size diversity of the stock produced. As none of the species are particularly easily handled, a strategy of complete harvesting of single raceway units is Likely to be the most workable in the first instance.
Little is known about the actual growth rates of these stocks under local conditions, but assumptions may be made based on experience gained elsewhere. On this basis, given the expected slightly warmer temperature regimes, it is likely that for seabass and seabream, fish of 250 g and above would start to become available from August onwards in the second year of production, with fish of 350 – 400 g available before the end of the year. In the northern Mediterranean, stocks may be held until the spring or summer of the third year to reach 400 to 600 g in weight; this may also be done here, with these weights being reached slightly earlier (Fig. 7).
If the strategy is taken of harvesting during the end of the second year, peak flow requirements will be around 35 m3/minute for the initial 50 t production representing the first phase; this would rise to perhaps 40 m3/min if the stock were to be held over into the third year.
The use of tilapia, if timed carefully, would tend to even out these cyclical trends. On a typical 8–10 month growing season, stocks introduced in summer would reach market size in springtime, when capacity was otherwise underutilized. The precise management of stocks would however need to await actual performance results on site.
The production cycles so defined may be used as the basis for more detailed planning of water supply, power, feeds, and for the input of other resources. These will be detailed further in later sections.
