56 MARCH 2018 • WORLD AQUACULTURE • WWW.WAS.ORG (10 percent). The mixture had 54.6 percent crude protein, 5.3 percent lipid and 6.5 percent moisture. Protein content of feeds ranged from 41.4 percent (control) to 42.3 percent for the diet with 75 percent fishmeal replacement. Ash content was 13.2 percent for the control, 11.2 percent for treatment A and 9.9 percent for the treatment B. Lipid content was 10.9 percent for the control diet, 9.1 percent for treatment A and 9.9 percent for treatment B. Fish were fed ad libitum once daily and were not fed when temperature exceeded 22 C. The culture period was 130 days. Water quality variables (temperature, DO, and pH) were measured twice daily in the early morning and before feeding in the afternoon. Ten percent of the fish population was sampled monthly to determine fish growth and health. At the end of the experiment all fish were weighed and feed conversion ratio (FCR, feed offered/weight gained), daily growth (DG, [final weight — initial weight]/time), protein efficiency ratio (PER, weight gained/protein offered) and specific growth rate (SGR, [ln final weight — ln initial weight]/t) were determined. For histological analysis, samples were fixed in 10 percent formalin and embedded in paraplast. Histological sections were stained with hematoxylin and eosin. Treatments groups were compared by one-way ANOVA (Hintze 1998). Study Results Mean water temperature was 20.8 C, with maximum temperatures of around 25 C occurring in October at the end of the trial. Mean dissolved oxygen was 7.9 mg/L and was minimum in August with a concentration of 4.5 mg/L (Fig. 3). Average water pH was 7.6, with slight daily variation between 7.2 and 7.9. Growth rate, final body weight, feed conversion, protein efficiency ratio, and nutrient content of fillets of rainbow trout fed the three feeds were not significantly different (Fig. 5, Table 2). Fish grew from 45 g to about 190 g in 130 days, for a growth rate of 1.1 g/d. Trout fed the two fishmeal replacement diets reached satiation before those fed the diet containing only fishmeal, but this did not affect fish growth. Although not a significant difference, feed conversion ratio was slightly lower in treatments with the fishmeal replacement ingredient mixture. Protein efficiency ratio ranged from 1.52 to 1.56, with a slight trend towards better utilization of protein in the two experimental diets. FIGURE 3. Dissolved oxygen concentration (OD) and temperature (T) measured during the production period. FIGURE 4. Rainbow trout at harvest were around 190 g. FIGURE 5. Trout growth curves obtained with different diets. FIGURE 6. Architecture of hepatic parenchyma with a centrilobular vein (VC) (H-E, 20x). TABLE 2. Production performance of trout fed three different diets for 130 days. Treatment B Treatment A Control (75%) (50%) Initial weight (g) 42 44 50 Final weight (g) 185 187 193 FCR 1.72 1.77 1.89 PER 1.54 1.56 1.52 DG (g/day) 1.1 1.1 1.1
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