Nuevo Aviso

Production of farm-reared shrimp has increased significantly in tropical and subtropical areas of the world (In 2003, shrimp aquaculture exceeded 1.6 million mt). This rapid expansion has led to a series of studies ranging from static and integrated farming systems (Burford et al., 2003), treatment of farm effluents (Tilley et al., 2002; Jackson et al., 2003) to the use of alternative ingredients in shrimp feeds (Smith et al., 2000; Forster et al., 2003). Contradictorily, little attention has been given to the improvement of feed management practices, despite their potential to reduce economical and environmental pressure in shrimp farms.

Traditional shrimp feed management combines population sampling to estimate gains of stocked shrimp biomass, the use of feeding tables to adjust weekly feed rations, and, sometimes, the daily monitoring of feed remains from feeding trays to serve as an indicator of feed consumption and population survival (Pontes et al., 2006). Feeding rates, times of feed delivery, feeding frequency and feed dispersal method vary considerably depending on the farmed species, shrimp body weight, farm size, intensification level and water and feed quality. (Carvalho and Nunes, 2006). Although some countries have adopted more complex feeding protocols (Nunes and Suresh, 2001; Nunes, 2003, 2004), most feed management technologies have remained practically unchanged since the mid 1980s (Carvalho and Nunes, 2006).

In shrimp grow-out, it has always been thought that a higher number of daily rations led to a faster shrimp growth, a better feed conversion efficiency and an improved water quality (Robertson et al., 1993; Jaime et al., 1996). However, more recently, opposing data have suggested no benefit in multiple feed rations in Litopenaeus vannamei and Penaeus monodon culture (Velasco et al.,1999; Smith et al., 2002) and this is because traditional practices do not consider the shrimp physiological factors involved, leading to inefficient use of the feed and resulting in the consequent economic and environmental losses.

Most animals live in an environment where sunlight intensity, temperature, and consequently other factors such as food availability and risk from predation vary considerably with a regular 24-hr cycle. Thus the ability to modify physiology and behavior appropriately at certain times during the day–night cycle is essential for survival (Vallone et al., 2007).

A key adaptation that allows animals to anticipate environmental changes has been the development of a self-sustaining 24-hr timing mechanism or “clock” (Pittendrigh, 1993). These 24-hr biological clocks characteristically continue to function even under artificial conditions where animals are deprived of environmental changes. Even though the behavioural activities of shrimp have been sporadically investigated in the laboratory (Primavera and Lebata 1995; Guerao & Ribera 1996; Pontes 2006),

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