Influence of turbidity on group level responses to feeding in the Pacific white shrimp (Litopenaeus vannamei)

The use of behaviour as a tool to improve welfare conditions within aquaculture is increasing, and our understanding of individual and group behaviour of commercially important penaeid shrimp has grown in recent years. However, the majority of studies investigating shrimp behaviour have used clear water conditions allowing for easier observation. Little is known about the influence of water turbidity on the feeding behaviour and social interactions of penaeid shrimp even though they are commonly reared for aquaculture in highly turbid ponds. Here, the behaviour of groups of four Litopenaeus vannamei juveniles (n = 144; 6.42 +/- 0.28 g, mean +/- S. E., body mass) was observed at three different turbidities; clear water (approximately 2 NTU, Nephelometric Turbidity Unit), medium turbidity (approximately 14.5 NTU) or high turbidity (approximately 30 NTU). Groups of shrimp were observed for 20 min within an experimental arena provided with feed, and video footage analyzed using an automated tracking software (EthoVision XT V14). Feed intake was greater in the high turbidity treatment compared to clear water, although no differences in behaviours related to the feeding area (e. g. time spent feeding, latency to feed) were found between treatments. Turbidity influenced exploratory behaviours, where shrimp held at the medium turbidity were more active than in the other treatments. Shrimp held in high turbidity also moved much more closely to each other than in the other treatments. These results highlight the importance of accounting for turbid water conditions when studying shrimp behaviour.