We examined the relative growth of threespine sticklebacks collected from 11 lowland streams in southeastern England during late autumn to test for between-catchment variations as well as development-related shifts in morphology. And, to understand better the sympatric relationship between threespine Gasterosteus aculeatus and ninespine Pungitius pungitius sticklebacks in small lowland streams, we compared growth variability in 35 mensural characters and morphological indices related to functional morphology in adults from one of these sites. Threespine demonstrated great plasticity, with some morphological differences observed between stream catchments, mainly in ventral spine and dorsal spine length, pre-anus and preanal distances, fin depth, and ventral body width (represented in the basipterygium medial plate width). Developmentally, three groups of mensural characters were found: 18 characters best explained by a linear regression (isometric growth), 9 characters best explained by a quadratic equation (gradual allometry), and 8 characters best explained by a split-linear regression (mainly isometric growth, with an abrupt shift in proportional growth – between 40 and 58 mm SL). However, these shifts did not appear associated with common ecological, physiological and/or behavioural functions. Compared with ninespine stickleback, threespine has a more robust body with stronger and more prominent spines, shorter tail, and eyes situated more backwards. Functional morphological indices suggest threespine to be a slower but more manoeuvrable swimmer than ninespine, which acquires a relatively more cruiser-form shape with reduced drag and more lift.
To address the dearth of information on the biology of white-eye bream in its novel range of Europe, we examined the morphology and growth rate of specimens inhabiting a dam reservoir on the lower Vistula River and compared the results with those from other waters of native and non-native regions of this species. Altogether, 24 mensural and 15 qualitative characters of 93 individuals (45 females and 48 males) as well as age of 108 specimens were determined. Body length (l) of the fish ranged from 142 to 277 mm. To examine the patterns of relative growth, relationships between 21 mensural characters (raw data) and l were tested using a non-linear regression analysis: 5 characters were best described by a linear function, 5 by a power one, 10 by a quadratic and 1 by a split-linear regression. There were significant differences in morphometric characters among the studied population and those from the Zegrze Reservoir (Vistula River catchment) and the Dnieper River, suggesting substantial morphological plasticity of white-eye bream. Meristic characters (the basic characters are expressed by the following formula: l.l. 50-57; D II-III 7-8; A III-IV 36-43; P I-III 15-18; V I-III 8-9; C IV-VII 16-18; sp.br. 18-25; 5-5) showed considerable overlap with the literature data except the number of unbranched fin rays, which revealed greater variability. The growth rate of the white-bream from the Włocławek Reservoir was moderate in the first year of life, and then it was faster than in many waters from its native range. This marked increase of growth rate seemed to be site-specific rather than region-specific, and associated with particularly rich feeding resources (abundant bottom fauna) of the eutrophic and strongly flowing dam reservoir.