Is batch variability in hatching time related to size heterogeneity and cannibalism in pikeperch (Sander lucioperca)? Svend Steenfeldt, Ivar Lund & Erik H˛glund Section for Aquaculture,The North Sea Research Centre,Technical University of Denmark, DTU-Aqua, Hirtshals, Denmark Correspondence: S Steenfeldt, Section forAquaculture,The North Sea Research Centre,Technical University of Denmark, DTU-Aqua, PO Box101, DK-9850 Hirtshals, Denmark. E-mail: sjs@aqua.dtu.dk Abstract Larval size heterogeneity is known to induce canni- balism, and procedures to avoid larval size di¡er- ences are consequently implemented already during egg incubation and hatching.We investigated the re- lation between larval development variability, size heterogeneity and cannibalism in pikeperch. Larvae were sorted into ¢ve groups according to the time of hatching during a 65-h period. The larvae with di¡er- ent times of hatch were then reared separately or to- gether during an 18-day period. Late hatched larvae were longer ( P 5 0.003) and had less yolk remaining ( Po0.001) than early hatched individuals at the time of hatching. However, on 11 days post fertilization, the late-hatching larvae tended to have larger yolk reserves than earlier hatched individuals ( P 5 0.07). Furthermore, the next day, a lower proportion in the late fraction had switched to exogenous feeding ( P 5 0.024). That larvae with a late hatching time devel- oped slower suggests a positive relationship between the hatching time and the embryonic developmental rate. However, di¡erences in the length and available yolk re- serves at hatching between larval fractions with di¡er- ent hatching times suggest that hatching is not strictly associated with a speci¢c developmental stage, and that factors other than the development rate of the embryo are involved in the timing of hatching. Keywords: Pikeperch, Sander lucioperca, hatching time, ¢rst feeding, size heterogeneity, cannibalism Introduction Pikeperch ( Sanderlucioperca ) is a promising candidate for intensive aquaculture due to its high potential growth rate, density tolerance and high temperature preference (Hokanson 1977; Wang, Xu & Kestemont 2009). However, pikeperch is highly piscivorous and the cannibalistic behaviour of pikeperch is a chal- lenge to successful intensive rearing of this ¢sh (Kes- temont, Xueliang, Hamza, Maboudou & Toko 2007). Cannibalism is often categorized as type I and type II. In type I cannibalism, the prey is only partly ingested, whereas in type II, the whole prey is swal- lowed (Kestemont, Jourdan, Houbart, Me¤ lard, Paspa- tis, Fontaine, Cuvier, Kentouri & Baras 2003). The intensity of cannibalism is generally determined by the ratio between predator gape size and prey size (Smith & Reay1991). A high predator to prey gape size ratio is usually required in type II cannibalism (Cu¡ 1980; Hecht & Applebaum 1988; Van Damme, Apple- baum & Hecht 1989; OtterÔ & Folkvord 1993; Baras, Maxi, Ndeao, & Me¤ lard, 2000). Size heterogeneity between predator and prey within a batch can be caused by multiple factors in- cluding parental, abiotic as well as biotic factors (Gef- fen 2002). One of the underlying factors for inducing size heterogeneity within a batch may be individual di¡erences in larval development; larvae reaching time to ¢rst feeding early may later grow faster than the remaining larvae in the batch. This has been de- monstrated in salmonids, where fry developmental rate has been related to future growth and survival (Metcalfe & Thorpe,1992; Sundstr˛m, Lohmus & Dev- lin 2005). Furthermore, during the egg and yolk sack stages, the development is mostly dependent on inter- nal resources and individual metabolism (Kamler 2008). Individual di¡erences in oxygen consumption in larvae end eggs (Bang, GrÖnkj×r & Malte 2004; Regnier, Bolliet, Labonne & Gaudin 2010) suggest Aquaculture Research, 2011, 42 , 727^732 doi: 10.1111/j.1365-2109.2010.02681.x r 2010 Blackwell Publishing Ltd 727