Effect of inclusion of dried Tetraselmis suecica on growth, feed utilization and fillet composition of European sea bass juveniles fed organic diets

In the fish industry, bloodspotting represents one of the major causes of fillet downgrading and adequate bleeding is considered necessary for good product quality. The total blood volume of different fish species ranges from 1.5 to 3.0% (Huss, 1995) up to 5 to 7% (Itazawa et al., 1983) of the body weight. According to Robb et al. (2003) and Roth et al. (2005), muscle activity during bleeding is not important for blood drainage. There is also some disagreement about what is the best bleeding method. However, it seems that immediate bleeding of live fish after capture or stunning is more important than the bleeding method (Valdimarsson et al, 1984; Botta et al., 1986; Roth et al. 2005). In case of Atlantic salmon, perimortem stress did not imply poorer drainage of blood. However, the study was conducted in a prerigor context only. It was therefore speculated whether filleting and washing before the blood had time to coagulate actually could mask the effects of stress (Erikson et al., 2010). Pre-rigor filleting can improve efficiency at the processing plant, as processing of the fillet products is then performed directly after slaughter, instead of 3 - 5 days later when rigor mortis is resolved. A few investigations have been carried out with respect to quality effects of pre-rigor cod fillets (Lauritzsen et al. 2004; Kristoffersen et al. 2006; Mørkøre, 2006; Tobiassen et al., 2006), and both positive and negative quality aspects have been reported. Kristoffersen et al. (2006) observed less gaping in pre-rigor Atlantic cod (Gadus morhua) fillets, but a significantly higher liquid loss and 12-13% shorter fillets compared to post-rigor fillets. Lauritzen et al. (2004) concluded that pre-rigor salting of cod lead to a larger reduction in weight, a higher water loss and a lower uptake of NaCl than post-rigor salted fish or fish salted after frozen storage. Tobiassen et al. (2006) considered pre rigor processing a better concept for distribution and sale of high quality fresh fillets since pre rigor fillets exhibited less gaping, firmer texture and slower bacterial growth after filleting. The main objectives of the study were to (a) assess the effect of perimortem stress on blood drainage, (b) compare the efficiency of gill cutting and direct gutting as bleeding methods, and (c) compare pre- and post-rigor filleting strategies in terms of residual blood.