Effects of stocking density on feeding behavior of Penaeus vannamei

Intensive farming of shrimp in commercial ponds is rapidly increasing in order to meet growing commercial demands, and determining the correct stocking density is an important issue for the shrimp industry
.
Increased stocking density resulted in increased competition among individual shrimp, decreased feeding efficiency, and increased water degradation
.
In addition, at high densities, shrimp production feed conversion, growth and survival rates are affected
.
Therefore, determining the appropriate stocking density plays an important role in successful rearing
.
The aim of this study was to investigate how the feeding behavior of Penaeus vannamei was altered according to stocking density
.
The study also evaluated the applicability of Nordas' animal tracking system (EthoVision XT) to automatically track shrimp feeding behavior in a group environment
.


Experimental procedure
The shrimp were acclimated and acclimatized in a closed system two weeks before the official start of the experiment
.
In the formal trial, 56 shrimp in good condition were selected and the shrimp were assigned to one of three different densities: low density (two shrimp), medium density (four shrimp) and high density (eight shrimp), corresponding to 6.
2 Shrimp/m², 12.
4 prawns/m² and 24.
8 prawns/m²
.
Depending on the density, the prawns were marked with different colors (red, yellow, blue, or black) and positions (left or right eye stalk) (Figure 1) so that all individuals could be identified
.
There are four groups under each density
.
The shrimps of each group were placed on the test site together with the feed and recorded for 20 minutes, and each group recorded 8 times continuously
.
Observation and video analysis were automated using EthoVision tracking software during the trial, and behavioral data for all individual shrimp in each trial was obtained through EthoVision's social interaction module
.

figure 1

 
Nordas' animal trajectory tracking system (EthoVision XT) can provide a large number of parameters to help researchers conduct in-depth analysis of experimental results
.
Vannamei behavior tracked by EthoVision in this trial included: time spent in feeding area, attraction score to feeding, number of transitions to feeding area, average distance to feeding throughout the trial, travel time, distance traveled by shrimp, duration of trial average speed, distance between individuals, and physical contact (Table 1)
.

Table 1

 

Test results
(1) Reliability of animal movement trajectory tracking system
In the statistical process, the five behavioral data (feeding time, feeding attraction, transition, movement, and body contact) tracked manually by the observers were compared with the automatically observed behavioral data of EthoVision Make a comparison
.
Manual observations were significantly similar to automated observations obtained from EthoVision (Fig.
2): time spent in the feeding area (98.
0% similarity, Fig.
2a), feeding attraction (97.
0% similarity, Fig.
2b), number of transitions ( 93.
4% similarity, Fig.
2c), movement time (93.
4% similarity, Fig.
2d) and body contact (95.
0% similarity, Fig.
2e)
.

figure 2

 

(2) The effect of density on shrimp behavior The
data results showed that density had a significant effect on the timing of the feeding area (Fig.
3a)
.
Medium-density shrimp spent more time in the foraging area than low- and high-density shrimp
.
Density had no effect on feed attraction (Fig.
3b)
.
Density had a significant effect on the number of transitions to the feeding area (Fig.
3c), with more transitions for high-density shrimp at medium and low densities
.
No significant difference was found between feeding distance and density (Fig.
3d)
.

 
Within the test site, there was a significant difference in travel time (Fig.
3e), with shrimp at low densities showing greater activity than those at medium and high densities
.
Likewise, density had an effect on travel distance (Fig.
3f), with low-density shrimp traveling farther than medium- and high-density shrimp
.
The moving speed of shrimp was also affected by density (Fig.
3g), with low-density shrimp having higher speeds than medium- and high-density shrimp
.

 
In terms of social behavior, there were differences in the distance between shrimps (Fig.
3h), and the distance between shrimps at low densities was greater than that at medium and high densities
.
Likewise, there was a difference in the physical contact time (Fig.
3i), with the low density shrimp having less physical contact time compared to the medium density and the high density
.
In addition, physical contact time was significantly reduced at medium densities compared to high densities
.

image 3

 

Figure 4

Figure 5

 

Image 6

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