Amongst the non-native Ponto-Caspian gobies that have invaded the Middle Danube is the monkey goby Neogobius fluviatilis (Pallas, 1814). Despite a strong specialization towards sandy substratum, revealed in a previous study, monkey goby is considered an invasive species and therefore should demonstrate great plasticity in its biological traits. The main aim of the present study was to evaluate the age and growth of a non-native population of monkey goby from the River Ipeľ in Slovakia. Six age groups (0 – V) were observed in the sample from the River Ipeľ (n = 165), with males demonstrating faster growth than females, which was reflected both in the smoothing cubic B-spline model and in the annual increment. The cubic B-spline model indicated a reverse Lee’s phenomenon, especially in males, which is likely to have arisen from the size selective mortality. Growth of invading monkey goby from the River Ipeľ was slower than that reported for the species’ native range. Together with other growth patterns, this may suggest (among other possible explanations) a greater allocation of resources to reproduction than to somatic growth, which is a life-history pattern typical for newly established populations of successful invaders.
Growth patterns of the golden loach, Sabanejewia balcanica were examined in the Rijeka River in Central Croatia on a total of 77 specimens collected in a single sampling session in June 2006. No significant difference was found in total body length between males and females. Age was determined from otoliths. Both males and females live 4 years, though due to the sampling period, no 0+ age fish were found in this study. The length-weight relationship was calculated as W=2x10-6TL3.3229 for males and W=3x10-6TL3.2811 for females, indicating positively allometric growth. According to the growth factor k, growth of males was three times faster than that of females.
Lake Biwa consists of a large, deep north basin and a small, shallow south basin, and the body weights of bluegill Lepomis macrochirus in the north basin tend to exceed those in the south basin. To elucidate the cause of this phenomenon, the physical characteristics of the fish in the two basins were compared. The fish in the north basin had larger gonads and stomachs than did the fish in the south basin, but the contributions of these organs to the body weight were very small. The body weights of the fish in the north basin still exceeded those in the south basin after the subtraction of the weights of the gonad and stomach. Bluegill in the north basin had deeper
bodies than those in the south basin. The heavier body tissues of bluegill in the north basin appear to be an adaptive response to the colder environment. Given the flourishing of largemouth bass Micropterus salmoides
in the littoral zone in the north basin, the deeper bodies of bluegill there may contribute to their increased survival rate by reducing their vulnerability to predation by largemouth bass.