Introduction
Behavior interactions are a key component of social dynamics in group-reared fish and can significantly influence welfare and production efficiency (De Verdal et al., 2019). In Nile tilapia (Oreochromis niloticus), aggression is often associated with feeding events, yet quantitative data comparing feeding and non-feeding contexts under commercial tank conditions remain limited (Fattah et al., 2021). The increasing need to reduce reliance on soybean meal in aquafeeds has driven interest in more sustainable alternative plant ingredients, including hempseed meal derived from Cannabis sativa. Hempseed meal has been proposed as a potential partial substitute for conventional protein sources in aquafeeds due to its lower environmental footprint and favourable amino acid profile. Dietary composition can influence feeding dynamics and competition, potentially affecting social interactions in group reared fish (Ward et al., 2006). However, hempseed meal effects on behaviour in socially dynamic rearing systems remain largely unexplored. This study aimed to quantify aggressive behaviour across feeding and non-feeding periods over a six week trial and to assess whether dietary inclusion of hempseed meal influences aggression patterns in Nile tilapia.
Materials and Methods
Six 200 L glass tanks (control and hempseed meal diets; n = 3 per treatment) stocked with 28 Nile tilapia per tank were video recorded during weeks 2, 5, and 6; with three recording sessions per week during both morning and afternoon feeding events. All tanks were connected to the same recirculating aquaculture system (RAS). The hempseed diet was formulated by replacing 30% of the control diet with hempseed meal, while the control diet represented a standard commercial formulation. Video cameras were installed at the front of each tank and recordings of 2h were conducted from 1h before feeding started. Behaviour was quantified from 20 min video segments, with one segment analysed per tank, week, replicate, and context (feeding or non-feeding), resulting in 18 segments per tank (n = 108 total). Segments representing non-feeding and feeding contexts were derived from morning and afternoon recordings, respectively. Recordings were annotated using BORIS (Behavioural Observation Research Interactive Software; v9.7, Friard & Gamba, Italy), and aggressive acts were classified as nipping, chasing, lateral fights, and mouth fights. Aggression counts were analysed using a generalized linear mixed model (GLMM) with a negative binomial distribution and log link in IBM SPSS Statistics (v31, IBM Corp., USA).
Results
Feeding context strongly affected aggression, with lower counts of aggressive events across all behaviour types during feeding than non-feeding periods (IRR = 0.55, p < 0.001). Behaviour type explained most variation (p < 0.001), with chasing occurring approximately twice as frequently as nipping, while lateral and mouth fights were less frequent. Aggression declined across weeks (p < 0.001). Diet affected aggression (p < 0.001), with higher counts observed in the hempseed treatment compared to the control, but also higher final weight and improved feed conversion ratio compared to the control. Recording replicate had no significant effect (p = 0.113), and no diet × period interaction was detected (p = 0.328).
Discussion
The reduction in aggression during feeding suggests that fish prioritise feeding over social interactions, leading to a temporary suppression of aggressive behaviour (Montero et al., 2009). Differences among behaviour types indicate that low intensity interactions, such as chasing, dominate the aggression profile, while more energetically costly behaviours occur less frequently. The decline in aggression across weeks may reflect progressive social stabilisation within groups. Although diet affected overall aggression levels, the absence of a diet × period interaction indicates that dietary effects were consistent across feeding contexts and did not alter the behavioural response to feeding. The higher aggression observed in the hempseed treatment may reflect increased feeding motivation rather than a direct behavioural effect (Cutts et al., 2001; Peake & McGregor, 2004).
Acknowledgment
The project leading to these results has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 871108 (AQUAEXCEL3.0). The fish trial was completed at Wageningen University and Research (WUR), under grant agreement PID32385 (TNA programme).
References
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