Feeding Behaviour, Swimming Activity and Boldness Explain Variation in Feed Intake and Growth of Sole (Solea solea) Reared in Captivity

The major economic constraint for culturing sole (Solea solea) is its slow and variable growth. The objective was to study the relationship between feed intake/efficiency, growth, and (non-) feeding behaviour of sole. Sixteen juveniles with an average (SD) growth of 2.7 (1.9) g/kg0.8/d were selected on their growth during a 4-week period in which they were housed communally with 84 other fish. Selected fish were housed individually during a second 4-week period to measure individual feed intake, growth, and behaviour. Fish were hand-fed three times a day during the dark phase of the day until apparent satiation. During six different days, behaviour was recorded twice daily during 3 minutes by direct observations. Total swimming activity, frequency of burying and of escapes were recorded. At the beginning and end of the growth period, two sequential behavioural tests were performed: “Novel Environment” and “Light Avoidance”. Fish housed individually still exhibited pronounced variation in feed intake (CV = 23%), growth (CV = 25%) and behavior (CV = 100%). Differences in feed intake account for 79% of the observed individual differences in growth of sole. Fish with higher variation in feed intake between days and between meals within days had significantly a lower total feed intake (r = −0.65 and r = −0.77) and growth. Active fish showed significantly higher feed intake (r = 0.66) and growth (r = 0.58). Boldness during both challenge tests was related to fast growth: (1) fish which reacted with a lower latency time to swim in a novel environment had significantly higher feed intake (r = −0.55) and growth (r = −0.66); (2) fish escaping during the light avoidance test tended to show higher feed intake (P<0.1) and had higher growth (P<0.05). In conclusion, feeding consistency, swimming activity in the tank, and boldness during behavioral tests are related to feed intake and growth of sole in captivity

Classification of fish based on their growth in period 1^a.

a<p>Two random fish per growth class were selected.</p>b<p>BW = Body weight is averaged over the total number of fish categorized in each growth class.</p

Relationship between swimming activity (%) in the home tank and A) total feed intake (g/kg^0.8/d) and B) residual feed intake (g/kg^0.8/d) of 15 individually housed sole.

<p>Regression equations are A) FI = 3.63+0.12*SWIM (R² = 0.44, P<0.05) for feed intake and B) RFI = −0.15+ 0.03*SWIM (R² = 0.10, P>0.1) for residual feed intake.</p

Relationship between total feed intake (g/kg^0.8/d) and the CV of feed intake between days (A) and between meals within days (B).

<p>Regression equations are A) y = 5.49−0.04× (R² = 0.43, P<0.01) and B) y = 7.17−0.06× (R² = 0.60, P<0.001).</p

Comparison of growth, feed intake and feed efficiency (RFI) between fish displaying escape behaviour (present vs. absent)^b.

<p>Values are means ±SE. Significant differences are indicated by;</p><p>*p<0.05;</p><p>+p<0.1; ns = not significant.</p><p>aRFI =  Residual feed intake/feed efficiency.</p><p>bClassification of the fish differs between observations in the home tank, the Novel environment test and the Light avoidance test.</p

Relationship between feed intake (g/kg^0.8/d) and growth (g/kg^0.8/d) of 15 individually housed sole.

<p>(FI = 0.79 + 0.68*GR, R² = 0.79, P<0.001).</p

Ethogram used for behavioural observations.

<p>Ethogram used for behavioural observations.</p