Pobreza y acceso a las Tecnologías de Información y

Low egg production per spawning and lack of spawning synchrony amongst tilapia females hinders the management of mass seed production (Jalabert and Zohar, 1982;

Little et al., 1993) and this impacts upon the tilapia industry as a whole. As a large number of parental stocks are required in order to meet the demand for seed (Little and Edwards, 1999; Mires, 1982), a hatchery operator has to maximise seed output by exploiting the reproductive potential of his/her broodstock (Macintosh and Little, 1995; Springate et al., 1984). Total seed output from Nile tilapia (O. niloticus), a

multiple spawner and maternal mouth-brooder, depends mainly on reproductive life span, fecundity of an individual female and frequency of spawning (Bhujel, 2000;

Lowe-McConnell, 1955; Lowe-McConnell, 2000; Nikolskii, 1969). Performance of broodfish in species having parental care may also include ‘‘brooding efficiency’’

(Lowe-McConnell, 1955; Lowe-McConnell, 2000; Welcomme, 1967). Large variations within and between the strains of tilapia have been reported for age at first maturity (Brummett, 1995; Hulata, 1982; Jalabert and Zohar, 1982; Macintosh and Little, 1995), fecundity (Babiker and Ibrahim, 1979; De Silva, 1986; Lowe-McConnell, 1955; Lowe-Lowe-McConnell, 2000; Pullin et al., 1986) and frequency of spawning (Jalabert and Zohar, 1982; Lowe-McConnell, 2000; Macintosh and Little, 1995; Peters, 1983; Philipart and Ruwet, 1982; Welcomme, 1967). Various factors, namely genetic (Jalabert and Zohar, 1982; Uraiwan, 1988) environmental (Brummett, 1995; Duponchelle et al., 1998; Duponchelle et al., 1999; Duponchelle et al., 2000;

Duponchelle and Panfili, 1998; Hulata, 1982) and management techniques (Bhujel, 2000; Little, 1989; Little et al., 1993) affect the performance of Nile tilapia broodfish.

1.7.1 Fish oil in fish feeds

Clearly, aquaculture is heavily dependent on fish meal (FM) and fish oil (FO). The aquaculture sector is at the biggest consumer of fish oil, at about 835,000 tonnes (88.5% total reported fish oil production in 2006) (Tacon and Metian, 2008). Given the fact that supply from wild feed grade fisheries will remain static in the next decade the viability, growth and profitability of aquaculture could be negatively impacted (Pike, 2005; Pike and Barlow, 2003; Sargent and Tacon, 1999; Tacon, 2004; Tidwell and Allan, 2002). Over the past decade, global fish oil production has reached a plateau and is not expected to increase beyond current levels. It is of note that the

prices of FO are projected to rise significantly by 2020 (Delgado et al., 2003).

Furthermore, other issues like the contamination of FO with organic pollutants make the use of some FO for aquafeeds problematic. This is highlighted by the increasing international and national demand for safer and higher quality aquatic products (FAO, 2006).

Hence, there is a growing and pressing need for sustainable alternatives to FO and for the reduction of the dependence on FO for fish feeds. In fact, the need for reducing the FO share in aquafeeds has been underlined in numerous reviews, reports and scientific papers and it presents a considerable challenge for the future development of aquaculture (Delgado et al., 2003; FAO, 2006; Naylor et al., 1998; Sargent and Tacon, 1999; Tacon and Metian, 2008; Trushenski et al., 2006). There are numerous lipid sources with a potential use in aquafeeds as substitutes for FO, e.g. animal by products, vegetable oils, marine products from lower trophic levels (Moksness et al., 2004; Regost et al., 2003) and transgenic plants (Robert, 2006) and the use of ingredients of plant origin as sustainable alternatives to marine oils in aquafeeds is of great potential. Specifically, plant ingredients have high global availability at competitive prices, as compared to FO, and they have nutritional properties that can largely satisfy the nutritional requirements of the fish (NRC, 1993).

However, their use does present some problems and several challenges have to be met before successful replacement of FO with plant oils is achieved. There are a large number of plant ingredients that have been studied or used as substitutes for FO in aquafeeds. An understanding of the lipid and fatty acid requirements of tilapia is needed before we can embark on a successful program to replace fish oil with vegetable oils in commercial tilapia feeds. Tilapia, like other warm-water fish, are

more inclined to require greater amounts of n-6 fatty acids compared to n-3 fatty acids for maximal growth (NRC, 1993). However, the studies presented in this thesis focused on three dietary lipid sources cod liver oil (CO), palm oil (PO) and mixed palm and cod liver oil (9:1) ratio, on O. niloticus reproductive performance with the goal of replacement of fish oil with palm oil. The reason for the chosen 9:1 ratio PO and CO was to reduce the proportion of n-3 to n-6 (M. Bell, personal communication).

1.7.2 Palm oil in Nile tilapia diets

Palm oil (PO) is derived from the oil palm (Elaeis guineensis family: Arecaceae).

Palm oil is a fruit flesh oil; however, seed oil (palm kernel oil) is also produced (Hertrampf and Piedad-Pascual, 2000). Palm oil has a high availability as its production provides one of the largest vegetable oil (VO) tonnages in the world, along with soybean oil (FAO, 2005; U.S.Department for Agriculture, 2007). Interestingly, it is also predicted to exceed soybean oil production within the next few years to become the most abundant VO in the world (Gunstone, 2001).

Crude palm oil has a very high content of 16:0 and 18:1n-9 (43.5% and 36.6% of total lipid fatty acid composition, respectively) and relatively low levels of 18:2n-6 (9.1%) (Ng et al., 2002; Ng, 2002; NRC, 1993). This fatty acid composition (FA) composition makes PO a good potential candidate to replace FO in diets for O niloticus to provide energy for sufficient growth. The use of PO in the diets of tilapia and other species such Atlantic salmon and rainbow trout has been investigated with regards to growth and feed utilisation efficiency, and changes in tissue FA composition and FA metabolism, give promising results (Bell et al., 2002; Caballero et al., 2002; Ng and Chong, 2004; Ng et al., 2003, 2004; Rosenlund et al., 2001;

Torstensen et al., 2000).