Growth, age and size structure of the introduced pumpkinseed (Lepomis gibbosus L.) population from small ponds along the Vit River (Bulgaria).
The age and size structure, length and weight growth of the introduced fish species Lepomis gibbosus L. was studied. The study area included four small artificial lakes, part of lake's system ("adaptive ponds") that serve as a buffer zone between the oil refinery "Plama" (city Pleven) and the River Vit (North Bulgaria). Four age groups were observed (1+ to 4+). Small-sized fish dominated, standard size of 46 to 55 mm comprised 38% of the entire stock. The relationship between standard length (SL) and scale radius (R) was: SL=0.1253R+1.124; TL=0.1522R+2.3048 for total length respectively. The maximum-sized fish (SL) that was observed was 92 mm. Von Bertalanffy length grow curve is presented by the follow equation: SLt=95 [1-e-0.32(t-0.05)]. Weight-length relationship for pumpkinseed population is expressed by the equation: W=0.0245SL3.187. Compared with other European pumpkinseed populations, the current stock was characterized by lower annual weight and length growth, simple age structure and domination of fish with relatively low sizes.