The reproductive biology of the marbled goby, Pomatoschistus marmoratus (Risso, 1810), was studied in the Strymon River estuarine system (northern Greece) between September 1997 and August 1999. Samplings were conducted on a monthly basis at the mouth of the river using a bag seine net and overall a total of 4 563 individuals were collected. The total length of males ranged between 2.5 and 6.0 cm and that of females between 2.8 and 5.7 cm, while that of unsexed individuals ranged between 1.2 and 2.9 cm. Sex ratio was 1.54:1 in favour of the females and statistically different from unity. The spawning of the species was extended, occurring between February and May. Mean absolute fecundity (F) was 1 386 (SE=8) oocytes and showed a significant positive exponential relationship with total length (F=14.387TL2.92), and total weight (F=1351TW0.83) of the fish. The relative fecundity ranged between 878 and 3 444 oocytes/g of total weight. Mean size at first maturity was estimated at 3.82 cm for the females and 4.66 cm for the males.
A bag-seine net (18-22 mm bar length mesh size) was used to collect two native, the Albanian barbel, Barbus albanicus Steindachener, 1870 and the chub, Leuciscus cf. svallize (Heckel et Knerr, 1858) and one introduced, the pumpkinseed, Lepomis gibbosus (Linnaeus, 1758), fish species of the Tavropos reservoir (western Greece). The soamtic lengths were linearly correlated to each other for all three species. B. albanicus and L. cf. svallize exhibited negative allometric growth, while the L. gibbosus grew isometrically. The mouth dimension were linearly or exponentially correlated to body size for all species. However, the mouth morphology differed among the species indicating differences in foraging ability and resource utilization. The lifespan of B. albanicus, L. cf. svallize and L. gibbosus in Tavropos reservoir was 21, 9 and 3 years respectively. The corresponding growth parameters were: L∞ = 47.0 cm, K = 0.064 yr-1, t0 = -2.76 yr for B. albanicus, L∞ = 24.3 cm, K = 0.257 yr-1, t0 = -1.46 yr for L. cf. svallize and L∞ = 11.9 cm, K ´0.506 yr-1, t0 = 1.67 yr for L. gibbosus.