Artificial seawater

Artificial seawater has been successfully used in closed system hatcheries. This makes it feasible to set up hatcheries far from coastal areas and close to, or integrated with, grow-out farms. The use of artificial seawater also considerably reduces risks, such as pollution, parasites, and the presence of prawn competitors and predators in larval rearing tanks. Productivity, using artificial seawater, can be higher than 40 PL/L; however, the cultivation period may be about 10% longer than when natural seawater is used (Mallasen & Valenti 1998a).

Studies aimed at freshwater prawn larval culture using artificial brackishwater have been successful in India (Reddy etal. 1991; Nair &Hameed 1992; Kanaujia et al. 1996) and Brazil (Valenti 1993; Silva 1995; Mallasen & Valenti 1997, 1998a,b). Commercial production using artificial brack-ishwater is also being performed in these two countries (Sebastian 1990; Valenti 1993) and all hatcheries in the USA use commercial artificial seawater with success (C. Upstrom, pers. comm. 2008).

Bidwell & Spotte (1985) presented several formulae for artificial seawaterpreparation. Complete formulations containing all the ions are expensive, difficult to obtain and non-feasible for commercial hatcheries. Suitable formulae with an incomplete ionic composition need to be species-specific. The use of artificial salt mixtures is not always successful (Daniels et al. 1992; New 1995). Research at Mississippi State University (W. Daniels, unpublished data) suggests that not all commercially available salt formulations are equally efficacious or properly formulated for larval crustacean production. Therefore, caution should be used in selecting one for hatchery production. Ions such as: Na+, K+, Ca2+, Mg2+, Cl-, Br-, HCO3- and possibly SO42- are essential for M. rosenbergii larval rearing (Zang etal. 1995; Mallasen & Valenti 1998b). The Mg2+ /Ca2+ ratio seems to be important and should be between 1.8 and 2.0 (Zang et al. 1995). On the other hand, the ions Al3+, Rb+, Zn2+, Co2+, Cu2+, Sr2+, Mn2+, HPO42-, L+, MoO42- and S2O32- may not be essential (Silva 1995; Mallasen & Valenti 1998b). However, some data suggest that the addition of Sr2+ may shorten the culture cycle (Araujo et al. 2002). Larvae reared in an artificial medium containing only essential ions reach the same weight as those reared in natural medium but there is a prolongation in the developmental

Table 5.2 Chemical composition of artificial brackishwater containing only essential ions, used at the UNESP Aquaculture Center (Centro de Aquicultura da Universidade Estadual Paulista - CAUNESP), Sao Paulo State University, Brazil.

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