Comparative study of pikeperch Sander lucioperca (Percidae; Linnaeus, 1758) eggs and larvae from wild females or from captive females fed chopped marine fish.

Morphometric characteristics, proximal composition and fatty acids profiles of eggs and larvae at hatching and mouth opening were studied as indicators for assessing the potential differences between spawns obtained from wild or captive females of pikeperch (Sander lucioperca). Captive females were acclimated to hatchery conditions and fed to satiation with chopped marine fish for more than a year, guaranteeing that captivity covered the full cycle of gonad maturation. The number of larvae obtained from the spawnings did not differ between captive and wild females, but both mean diameter and mean weight of the eggs collected from the captive females were significantly larger. Proximal compositions were similar in eggs and larvae from both groups, but fatty acids (FA) profiles showed striking differences: polyunsaturated FA consisted mainly of linoleic acid in eggs and larvae from wild females, while they consisted mainly of long chains of n-3 series in eggs and larvae from captive females. The diet of captive females largely modified the FA profiles of eggs and of hatching or mouth opening larvae, but did not affect the growth potential of early larvae, demonstrating that they were able to satisfy their early physiological needs regardless of the striking differences in their FA.

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.

Changes in some nitrogenous compounds in the blood and tissues of freshwater pikeperch (Sander lucioperca) during salinity acclimation.

The effect of ambient salinity changes (0.9, 6 and 12 psu) on the levels of dissolved ammonia (DA), ninhydrin positive substances (NPS), trimethylamine (TMA) and trimethylamine oxide (TMAO) in the blood and tissue of medium-acclimated Sander lucioperca L. (also Stizostedion lucioperca) were investigated. In freshwater, blood and tissue total free amino acid levels (measured as NPS) were 3.62 mM and 60.61 mM, respectively. The NPS content increased significantly (P<0.05) in the tissue and blood on acclimation to 6 and 12 psu salinities. The mass-specific tissue TMAO concentration of pikeperch acclimated to normal freshwater was 0.413+/-0.084 micromol TMAO g(-1). Results reveal that TMAO levels are positively influenced by the external salinity medium where significant differences in mean levels occurred between the groups (P<0.05). The calculated p[NH(3)] and [NH(4)(+)] gradients reveal that the [NH(3)] gradient was consistently low (cf. the [NH(4)(+)] gradient). The gradient of p[NH(3)] decreased with the medium increased salinities. The results suggest that freshwater pikeperch may be able to resist salinity changes by manipulation of nitrogen metabolism. Free amino acids and TMAO are involved in mediating response to salinity exposure in freshwater pikeperch.