Today, aquaculture is stagnating or declining in most European countries, while increasing by 7% worldwide. The European market is mainly dominated by a few species, such as Atlantic salmon (Salmo salar). The aim of the DIVERSIFY project is to promote the diversification of European aquaculture by developing the farming of new marine and freshwater fish species. Among these species, there is pikeperch (Sander lucioperca), for which three main bottlenecks prevent the success of larval rearing: a high rate of mortality mainly due to cannibalism, a high rate of deformities and a strong growth heterogeneity characterized by important differences in both size and developmental stages between larvae of the same cohort. Optimizing the rearing strategy appears as a major objective to improve both growth and decrease cannibalism. Considering various feeding strategies applied (Hamza et al. 2007; Kestemont et al. 2007; Szkudlarek et Zakes 2007; Lund et al. 2012), a study was carried out to determine the effects of four feeding factors on the growth, size heterogeneity and cannibalism on pikeperch larvae during the first two weeks post-hatching. A fractional factorial experimental design (24-1) of resolution IV was used to simultaneously study the effect of four factors with two modalities each and their possible interactions.

Pikeperch larvae were distributed in eight tanks (700 L) after hatching. The four tested factors were: quantity of live prey items (2 100 or 10 500 Artemia nauplii/larvae/day), weaning duration (three or nine days), frequency of food distribution (continuous or discontinuous) and use of co-feeding or not. The other parameters were controlled and checked every day. Photoperiod was fixed: 12h of light and 12h of darkness (Hamza et al., 2007) with a progressive increase of light intensity (from 0 to 5 or 50 lx) from 7:30 to 8:00 am and a decrease of light intensity (from 50 or 5 to 0 lx) from 7:30 to 8:00 pm. Water temperature was maintained at 20°C in all tanks (Kestemont et al., 2007; Szkudlarek and Zakes, 2007). Food was given every 1.5 hours (Hamza et al., 2012; Kestemont et al., 2007) during light period for discontinuous distribution modality. Dissolved oxygen was maintained above 6 mg L-1. Every week, from four days post hatching (dph) and after the first feeding, 40 larvae were sampled in each tank. Individual weight, total length, deformity rate and inflation rate of swim bladder were measured or calculated at 18 days post-hatching (dph). To quantify the cannibalism, an observation of 5 minutes per day and per tank was done. The data were analyzed using a multifactorial method.

Significant effects were observed at day 14 of the experiment (corresponding to the 18th day post hatching) on pikeperch larvae growth (total length and weight) and growth heterogeneity (Coefficient of Variation). The mean body weight of pikeperch larvae was significantly higher when a higher quantity of prey items was distributed (20.10 mg vs 9.39 mg at day 14). Logically, similar effects were observed on larval length (1.35 cm vs 1.08 cm at day 14). Moreover, significant effects of the quantity of live prey items, the frequency of food distribution and the co-feeding were also recorded on growth heterogeneity. Finally, at day 14, a significant effect of the interaction between co-feeding and duration of the weaning period was observed. When a co-feeding was applied, the duration of the weaning period had no effect on larval size heterogeneity, whereas without co-feeding, a significant increase of size heterogeneity appeared when the weaning period was longer (13.9% vs 10.5%). The statistical analyses showed that the number of cannibalism acts was higher (2.8 vs 0.5) with a lower quantity of prey items. Furthermore, there was a significant interaction between the weaning duration and the quantity of food on the number of cannibalism acts. Indeed, there was significantly more cannibalism acts with a lower quantity of food and with a weaning duration of 3 days.

This experiment showed the impact of four nutritional factors on the development of pikeperch larvae during the initial  rearing phase. The amount of distributed food seemed to be the main factor affecting the development of pikeperch larvae and cannibalism but some effects of food distribution, co-feeding and weaning duration were also observed. These results will contribute to optimize the larval rearing protocol in order to reduce growth heterogeneity and cannibalism.

This project has received funding from the European Union’s Seventh Framework Programme for research, technological development and demonstration (KBBE-2013-07 single stage, GA 603121, DIVERSIFY).

References

Hamza N., Mhetli M., Kestemont P., 2007. Effects of weaning age and diets on ontogeny of digestive activities and structures of pikeperch (Sander lucioperca) larvae. Fish Physiol Biochem, 33: 121–133.

Hamza N., Kestemont P., Khemis I.B., Mhetli M., Cahu C., 2012. Effect of different sources and levels of dietary phospholipids on performances and fatty acid composition of pikeperch (Sander lucioperca) larvae. Aquaculture Nutrition, 18: 249–257.

Kestemont P., Xueliang X., Hamza N., Maboudou J., Imorou T. I., 2007. Effect of weaning age and diet on pikeperch larviculture. Aquaculture, 264:197–204.

Lund I., Skov P. V., Hansen B. W. 2012. Dietary supplementation of essential fatty acids in larval pikeperch (Sander lucioperca); short and long term effects on stress tolerance and metabolic physiology. Comparative Biochemistry and Physiology, 162: 340–348.

Szkudlarek M. & Zakes Z., 2007. Effect of stocking density on survival and growth performance of pikeperch, Sander lucioperca (L.), larvae under controlled conditions.