Allometric growth and reproductive biology traits of pikeperch Sander lucioperca at the southern edge of its range.

This study describes some biological traits (allometric relationship, reproductive biology and condition factor) of pikeperch Sander lucioperca at the southern edge of its range. Data were compiled from field studies between January 1997 and January 2009 in three Tunisian reservoirs. Overall, 1497 fish were caught, from which 1308 specimens were sampled and dissected. Sexually undetermined, male and female fish from the different sites exhibited similar allometric growth, expressed through the equation M(T) = 5 × 10(-6) L(T) (3·06) , where M(T) is the total mass and L(T) is the total length. The exponent value is slightly but significantly greater than 3, indicating positive allometric growth. Sex ratio (males:females) was 47:53 but remained balanced only up to 55 cm L(T) and changed with increasing size towards female dominance. Spawning occurred in March and early April according to the changes in female size-adjusted gonad mass or corresponding gonado-somatic index (I(G) ) values. Thermal conditions seemed favourable in February, but March corresponded to the period of equal day and night lengths and the switch towards longer days in terms of photoperiod. Changes in both size-adjusted M(T) or Fulton's condition factor and size-adjusted liver mass or hepato-somatic index (I(H) ) were clearly associated with reproduction. Reserves were consumed during spring in association with spawning efforts. Nevertheless, the delay before the reconstitution of reserves seemed relatively long (from early spring to late summer) although both thermal and trophic conditions could be considered favourable for active feeding of the fish.