Cannibalism of Atlantic cod Gadus morhua larvae and juveniles on first-week larvae

Abstract

Cannibalism in Atlantic cod Gadus morhua is widespread under both field and culture conditions, but no studies have been conducted on the behavioural ontogeny of cannibalism in this species. We carried out an experiment to investigate the onset and ontogenetic changes in cannibalistic behaviour of Atlantic cod during early developmental stages. Cod larvae were separated into 4 size classes (6, 9, 12 and 15 mm) to monitor cannibalistic activity on first-week (~4 mm) conspecific larvae. Five cannibalistic behaviours (fixation, aggression, fin nipping, attacking and engulfing) were monitored when the predator was introduced to the observation chamber. Cannibalistic attacks initially appeared in 9 mm predators, although 6 mm larvae showed prey interest and engaged in fin nipping behaviour. The 9 and 12 mm larvae engaged in similar rates of cannibalistic activity, while 15 mm fish demonstrated a significant increase. These behavioural changes appear to coincide with the morphological and physiological changes associated with juvenile metamorphosis, namely fin ray, vertebrae and stomach development. More importantly, our observations indicate that cannibalism reduces survival of conspecifics at earlier developmental stages than indicated by diet analyses alone.

Effect of size sorting on the survival, growth and cannibalism in pikeperch (Sander lucioperca L.) larvae during intensive culture in RAS

“…One of the major factors contributing to this phenomenon is the excessive variation in the size of fish in the cohort (Baras and Jobling, 2002;Kestemont et al, 2003;Puvanendran et al, 2008). The variation of the fish size may be due to behavioural factors like territoriality and dominance hierarchies (Jobling et al, 1993).…”

Timing and selectivity of mortality in reared Atlantic cod revealed by otolith analysis

“…On the other hand, the co-feeding with natural zooplankton during the first week of weaning may have limited the occurrence of cannibalism during this period. There were no incidences of cannibalism in a previous study on Atlantic cod, when the larvae were weaned at an average size smaller than 10 mm (Baskerville-Bridges and Kling 2000a), and this corresponds with behavioural studies where cannibalistic behaviour was first observed in cod from 9 mm (Puvanendran et al 2008). Most of the R-group larvae in this experiment were thus probably too small to engage in cannibalistic behaviour at the onset of weaning, while the Z-group larvae reaching 15-20 mm length were in the size range with the highest cannibalistic propensity Puvanendran et al 2008).…”

“…There were no incidences of cannibalism in a previous study on Atlantic cod, when the larvae were weaned at an average size smaller than 10 mm (Baskerville-Bridges and Kling 2000a), and this corresponds with behavioural studies where cannibalistic behaviour was first observed in cod from 9 mm (Puvanendran et al 2008). Most of the R-group larvae in this experiment were thus probably too small to engage in cannibalistic behaviour at the onset of weaning, while the Z-group larvae reaching 15-20 mm length were in the size range with the highest cannibalistic propensity Puvanendran et al 2008). Clear signs of cannibalism were observed among large individuals shortly after the experiment, and for a stricter comparison of the effect of feed type per se, the R-group fish should have been reared until they had achieved the same size as the Z-group fish.…”

“…It has previously been shown that weaning in cod can result in agonistic behaviour and cannibalism due to an induced food restriction caused by the reduced availability of the preferred live prey during the transition to formulated feeds (Folkvord 1991;Baras and Jobling 2002). The initiation of agonistic behaviours in cod larvae have also been documented to occur earlier during ontogeny than previously thought (Puvanendran et al 2008), but documentation of the timing and extent of the selective mortality has proven difficult to assess. We therefore chose to use otolith microstructure analysis as a means to document the magnitude and timing of selective mortality in larval cod, and we carried out repeated samplings around the weaning period when the larvae change their diet from live feed to formulated feed.…”

“…Circles on top represent number of samples from different dates available for each group at each date. Data from replicate tanks are combined for visual clarity in these groups at onset of weaning (Puvanendran et al 2008) as well as a greater acceptance of formulated feeds in the R-groups (Koedijk et al 2010). However, the relative size difference as measured by CV of length did not differ notably between groups.…”