Gastric evacuation (GE) experiments were performed on brook trout Salvelinus fontinalis fed commercial food pellets. The experiments included small fish (36 g; 15 cm total length, LT ) fed meals of 0·2, 0·4 and 0·8 g and large fish (152 g; 23 cm) fed meals of 0·8, 2·0 and 4·0 g at temperatures ranging from 15·1 to 18·2° C. The stomach contents were thereafter sampled and weighed at 3 h intervals until the first empty stomach was observed. The course of GE was examined by use of a general power function of the data that revealed that the square-root function described the GE rate (GER) by the current stomach content mass independently of original meal size. Using the square-root function, the relationship between GER and fish size was described by a power function of fish length, whereas the effect of temperature was described by a simple exponential function. GER of the commercial pellets fed to S. fontinalis could thus be described by dStdt=-0·000464L1·31e0·052TSt (g h(-1) ), where St is stomach mass (g) at time t (h), L is total fish length (cm) and T is temperature (° C). The result of this study should provide a useful tool for planning of feeding regimes in production of S. fontinalis by optimizing growth and minimizing food waste.

No abstract

No abstract

Meat yield, biochemical composition, and fatty acid profile of farmed brook trout (Salvelinus fontinalis), Black Sea trout (Salmo trutta labrax) and their hybrids were compared. Hybrids contained significantly higher carcass and meat yield values than brook and Black Sea trout. Although the weight percent head and bone (brook trout as 13.14, 1.66 %, Black Sea trout as 13.52, 1.22 % and their hybrids as 13.92, 1.44 %) of the species were similar, fin, carcass, gonad, liver, internal organs and meat yield of the species were significantly different from each other (P<0.05).

A trial was conducted to evaluate the effects of the number of feeding days on feed consumption and growth of rainbow trout, Oncorhynchus mykiss (Walbaum) (initial mean weight 53.6 ± 11.3 g). Fish were held under natural winter–spring (40°57′N) photoperiod (L:8 D:16 – L:14 D: 10) and ambient water temperatures (4–12 °C) for 128 days, and fed on day 7 (F7), day 5 (F5.1: no feeding on weekends and F5.2: no feeding on Sundays and Wednesdays) or every other day (FEOD). Feeding treatments were replicated with 50 fish held in 200‐L tanks. Number of feeding days affected final live weight, with fish in group F7 achieving a mean weight of 285.6 g, followed by F5.1 (256.6 g), F5.2 (247.6 g) and FEOD (223.2 g). Final condition factors (CF) differed between the FEOD group and the others. Feed conversion ratios (FCR) exhibited significant differences among some of the groups. The results suggest that depriving rainbow trout of feed for more than 1 day a week has a negative effect on growth, but little influence on feed conversion.