WWW.WAS.ORG • WORLD AQUACULTURE • MARCH 2014 53 TABLE 1. Scores for four steps (orientation, approach, capture and ingestion) of the feeding response by dietary treatment in juvenile steelhead trout. Values are treatment means with standard deviation (n= 10). Diet Step 1 Step 2 Step 3 Step 4 Steelhead eggs 7.4 ± 3.9 7.3 ± 3.9 6.7 ± 3.7 6.1 ± 3.4 Commercial diet 5.8 ± 3.6 4.1 ± 2.7 3.5 ± 2.6 2.3 ± 2.6 Experimental diet 4.8 ± 4.4 3.9 ± 4.5 2.5 ± 3.6 1.8 ± 3.2 Experimental diet - red 5.0 ± 4.5 4.6 ± 4.4 2.7 ± 3.7 1.9 ± 2.8 (CONTINUED ON PAGE 54) the tank and given 15 minutes to acclimate to the chamber. During this time the underwater feeder was flushed three times with 1 L of water to acclimate the fish to the change in flow during feeding. Treatment diets were randomly assigned to each fish. A single food particle was loaded into the underwater feeder and flushed into the chamber using 1 L of tank water. Upon deployment of the particle, the fish was observed for 30 seconds. If the fish performed any of the following four steps of the feeding response outlined in Stradmeyer (1989) a ‘1’ was recorded. • Step 1: Orientation – head and eye movement, • Step 2: Approach – fish swims towards particle, • Step 3: Capture – fish makes contact with particle, • Step 4: Ingestion – fish retains particle for more than 10 seconds. For any of the steps that were not performed a ‘0’ was recorded. Thirty seconds of recovery were allowed when the observation period ended before the next particle was deployed. After ten particles of the treatment diet had been offered, the fish was removed from the study and all uneaten feed was siphoned from the chamber. Successful behaviors for each fish were then summed to create a score for each step of the feeding response. Dietary treatment did not affect feeding response as measured by any of the four behaviors (Table 1). A high degree of fish-to-fish variation (n=40) in feeding response made it difficult to identify significant differences among treatments. Steelhead eggs elicited the strongest feeding response at all steps with fish ingesting the egg on 61 percent of occasions. Feeding Study Tanks of 30 × 150 × 40 cm (180 L) were used in this study. A pebble substrate (as described previously) covered each tank bottom to a depth of 31 mm. Abernathy Creek water was provided to each tank at 11 L/min. Mean daily temperature during the study was 8.5 C and ranged from 5.9 to 12.3 C. Illumination was provided by fluorescent strip lighting on a natural photoperiod controlled by a photocell. Twenty hatchery-reared juvenile steelhead were randomly assigned to each of 20 tanks. The mean fork length was 115 ± 12 mm with a mean weight of 16 ± 5 g (n=20). The population in each tank was weighed at stocking and there were no differences in mean weight among treatments. All diets were presented to fish using an underwater feeder. As described previously, rations were flushed with 1 L of water to the bottom of each tank to simulate feeding in the natural environment. An additional treatment of the commercial diet offered by hand feeding at the surface was included. Feeding rate was adjusted weekly (Buterbaugh and Willoughby 1967) to account for changes in water temperature; however the feeding rate of eggs was fixed to match the caloric content of the other diets for that week. Three feedings were offered on Monday, Wednesday and Friday of each week. Tanks were cleaned every morning by removing the standpipe and allowing tanks to drain half way. After 60 days of feeding and 2 days of fasting, all remaining fish were weighed and measured individually. Growth and feed efficiency (FE) were significantly different among dietary treatments (Table 2). TABLE 2. Weight gain, specific growth rate, feed efficiency, condition factor, and survival of juvenile steelhead trout fed various diets for 60 days. Values given are treatment means ± standard deviation of 4 replications. Within a given column when letters differ indicates a significant (P<0.05) difference between the treatments. Diet Weight gain (%) Specific growth rate c Feed efficiency d Condition Factor e Survival (%) Steelhead eggs a 28.0 ± 1.6 zy 0.41 ± 0.03 zy 1.2 ± 0.1 zy 0.90 ± 0.01 98 ± 5 Commercial diet: hand-fed 33.8 ± 4.1 z 0.49 ± 0.06 z 1.3 ± 0.2 z 0.94 ± 0.03 96 ± 5 Commercial diet a 31.9 ± 4.2 z 0.46 ± 0.05 z 1.1 ± 0.1 zy 0.92 ± 0.01 86 ± 11 Experimental diet a 23.4 ± 4.2 y 0.35 ± 0.05 y 1.0 ± 0.1 zy 0.92 ± 0.03 89 ± 5 Experimental diet - red a 21.6 ± 2.4 y 0.33 ± 0.03 y 0.9 ± 0.2 y 0.91 ± 0.02 94 ± 5 Probability (P>F) b 0.0006 0.0008 0.0239 0.0829 0.123 a Indicates the diet was fed using the underwater feeder b Probability (P>F) of treatment differences as determined by ANOVA c Specific Growth Rate (SGR) = % weight gain / day d Feed Efficiency (FE) = Weight gain (per fish) / dry matter fed (per fish) e Condition Factor (K) = 100 x weight (g) / fork length (cm)3
RkJQdWJsaXNoZXIy MjExNDY=