Partial Substitution of Fish Oil with Microalgae (Schizochytrium sp.) Can Improve Growth Performance, Nonspecific Immunity and Disease Resistance in Rainbow Trout, Oncorhynchus mykiss.

The price of fish oil has reached a historical peak due to a consistent downward production trend, and therefore, the search for sustainable alternative sources has received great attention. This research was conducted to evaluate dietary micro-algae, Schizochytrium sp. (SC) as fish oil (FO) replacer in rainbow trout, Oncorhynchus mykiss. In the first trial, apparent digestibility coefficient (ADC) was 92.4% for dry matter, 91.4% for crude protein, and 94.2% for crude lipid in rainbow trout. In the second trial, six diets were formulated to replace FO at 0% (CON), 20% (T20), 40% (T40), 60% (T60), 80% (T80), and 100% (T100) with SC in the rainbow trout (3.0 ± 0.4 g, mean ± SD) diet. After eight weeks' feeding trial, weight gain (WG), specific growth rate (SGR), and feed efficiency (FE) of fish fed the T20 diet were significantly higher than those of fish fed other diets (p < 0.05). However, there were no significant differences in these parameters among those of fish fed CON, T40, T60, and T80 diets. Lysozyme activity of fish fed the T20 diet was significantly higher than those of fish fed other experimental diets (p < 0.05). After 10 days of disease challenge testing with pathogenic bacteria (Lactococcus garvieae 1 × 108 CFU/mL), the cumulative survival rate of fish fed the T20 diet was significantly higher than those of fish fed the CON, T80, and T100 diets. Therefore, these results suggest dietary microalgae SC is well-digested and could replace up to 80% of fish oil in the diet of rainbow trout without negative effects on growth and immune responses.

Temporal trends of PCBs in feed and dietary influence in farmed rainbow trout (Oncorhynchus mykiss).

As a rainbow trout producer, Italy is accounted as fifth in the world and second in continental Europe. In this study, the levels of the eighteen PCBs in feed and in trout, showed a statistical significant difference (p<0.01) throughout the years, with a declining trend from 2005 to 2010. This trend shows effectively that quality and safety of trout feeds has greatly improved during the last years and, as a consequence, also the PCBs values in muscle trout, showed a decreasing trend. Moreover, feed Σ18PCBs showed a statistical significant difference (p<0.01) among the analysed brands and was positively correlated (p<0.01 and r=0.451) with the rainbow trout muscle Σ18PCBs. These results showed that the presence of PCBs in trout muscle is directly linked to the chemical quality of aquaculture feed. The most commonly detected PCBs congeners were congeners PCB 153 and PCB 138 in all the three compared brands.