Data analysis was performed with STATISTICA software and included: control for Ž
. normality of raw data by the Kolmogorov–Smirnov test, analysis of variance ANOVA
between feeding protocols, followed by the Scheffe F-test for comparisons between
´
Ž .
Ž .
significantly different means P - 0.05 , and principal component analysis PCA for Ž .
classification as follows: 1 Frequency distribution of fish body weight between feeding methods: six distributions of fish populations from the respective feeding methods were
grouped and compared to the initial fish population; all of them were divided into 10 Ž .
equal weight ranges and data were expressed in percentage. 2 Daily feeding patterns resulting from the three self-feeding regimes in two time periods: 10 days at the
Ž .
Ž .
beginning SFL , SFM , SFH and 10 days at the end of this trial SFL , SFM , SFH .
i i
i f
f f
3. Results
Feeding protocol did not affect the survival of sea bass, which was high in all groups Ž
. Table 1 . The few dead fish did not have any external symptoms caused by disease or
cannibalism and their death was not related to their body weight nor did it coincide with any particular environmental event.
3.1. Growth and feed efficiency Growth was significantly affected by feeding protocol. Indeed, final mean body
Ž .
Ž weight BW was higher in self-fed groups than in AF50 and AF50M groups Table
f
Fig. 1. Change in SGR over the feeding experiment with European sea bass. Vertical bars indicate one Ž
. standard deviation
ns 3 . Columns within each period with different letter are significantly different Ž
. P - 0.05 . See text for details of feeding practices.
Fig. 2. Frequency distributions of initial and final body weight of European sea bass subjected to different feeding practices. See text for details of feeding practices.
. 1 ; the highest BW was achieved in the SFL group, with significantly higher values
f
than in all the automatic feeding groups. This trend for the highest growth in fish fed Ž
. using self-feeders with a low reward level SFL group was accompanied by a higher
Ž SGR and Gain compared to the other feeding protocols including SFM and SFH
Table 2 Ž
. Mean values S.D., ns 3 of N and P supply, gain and loss in groups of European sea bass subjected to
different feeding practices. See text for details of feeding practices Feeding practice
AF100 AF50
AF50M SFL
SFM SFH
U
Ž . N supply g
97.54.3 bc 41.50.7 c 40.13.4 c 126.514.7 bc 183.771.6 b 202.88.0 b
Ž . P supply g
14.90.6 bc 6.30.1 c
6.10.5 c 19.32.2 bc
28.110.9 b 31.013.6 b Ž .
N gain g 20.72.0 c
14.00.7 b 14.62.0 b 26.52.2 a 21.41.9 ac
22.12.7 ac Ž .
P gain g 5.70.6 c
3.90.2 b 4.10.3 b 7.00.5 a
5.50.6 ac 6.30.8 ac
N loss 101.49.3 ab
54.44.5 b 50.06.2 b 99.122.5 a 202.393.1 a 210.885.3 ab
y1
Ž .
g=kg fish gain P loss
12.21.0 ab 5.00.8 b 3.90.4 b 12.23.4 a
28.214.2 a 28.712.9 ab
y1
Ž .
g=kg fish gain
U
Ž .
Data with different letters are significantly different P - 0.05 .
. groups . A significantly higher growth rate was measured in self-fed fish in period 1
while in the remaining periods, fluctuation of SGR between feeding conditions was Ž
. similar Fig. 1 .
The total feed supplied was much higher in SFM and SFH groups than in the other Ž
. groups Table 1 , while in the SFL group, the feed supplied was similar to the AF100
group. FER was negatively related to feed supply, with the highest values in AF50 and AF50M groups. In the course of the trial, uneaten feed was only observed in AF100,
SFH and SFM tanks.
Ž .
The initial coefficient of variation in body weight CV was 19. CV was between
i f
20 and 27 at the end of the experiment, but was not affected by feeding protocol Ž
. Table 1 . However, PCA of frequency distributions in initial and final individual weight
Ž .
revealed significant differences in relation to the feeding practice Fig. 2 . The classifica- tion explained 81 of the total variance, and pooled the groups into three clusters: the
first one referred to the initial population and the SFL group with a high proportion of big fish, the second pooled the AF50 and AF50M group with a high percentage of
Ž .
Fig. 3. Histogram representation of the total number of feed demands open bars and the total feed supply Ž
. tilled bars in relation to feed reward level in self-feeding treatments with European sea bass. Vertical bars
Ž .
indicate one standard deviation ns 3 .
small fish, and the third pooled AF100, SFM and SFH where fish had intermediate features.
3.2. N and P gain and loss The effect of feeding protocol on N and P gain is shown in Table 2. Because feed
refusals could not be measured in this experiment, N and P retention are not presented. Ž
. N and P loss were affected by feeding treatment in the opposite way to FER Table 1 ,
Ž .
but were not related to nutrient gain Table 2 . The highest losses were observed in SFM and SFH groups where, as mentioned above, part of the demanded feed was uneaten.
Although N and P gain was higher in the SFL treatment than in the AF100 treatment, loss was identical in these groups. This result indicates the advantages of
using on-demand feeding systems for juvenile sea bass. However, groups of fish fed half the recommended level of feed had much lower N and P loss than fish subjected to the
other feeding treatments, indicating that the demand protocol used can probably be optimised.
3.3. Demand feeding actiÕity and rhythm In fish fed using self-feeders, there was a trend for a decrease in demand feeding
activity when the reward level increased, but this behavioural compensation was not Ž
. effective enough to accurately regulate the feed supply Fig. 3 . The feed supply was
Ž .
affected by the reward level Fig. 3 . Two main factors of PCA, covering 85 of the
Ž .
Fig. 4. Daily feeding patterns of European sea bass when self-fed at three reward levels ns10 . SFL, SFM, Ž .
Ž . and SFH are self-fed with low, medium, and high rewards, respectively. Subscript letters i and f in feeding
regimes refer to the initial and final patterns. Black, grey, and white bars correspond to night, crepuscular, and daylight hours of day.
total data variance, grouped the daily feeding patterns of self-fed fish into the following categories: a pattern of restricted daylight activity and a dusk peak at 2000 h was
Ž .
observed in all groups at the beginning of the trial SFL , SFM , SFH ; a pattern with a
i i
i
Ž .
diurnal peak at 0600–1100 h and a secondary nocturnal peak at 1900 h SFL , SFM ,
f f
and a pattern with a continuous increased diurnal activity and a secondary nocturnal Ž
. Ž .
peak at 1900 h SFH Fig. 4 . Regardless of the self-feeding regime, fish had a stable
f
low-demand feeding activity with a peak around dusk at the beginning of the trial. In Ž
contrast, they had increased their activity in specific hours of the day mainly morning .
and early night hours by the end of the trial.
4. Discussion
