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.
e determined regression relat ionships between head bone lengths and body size (standard length and weight) in chub Leuciscus cephalus and Eurasian perch Perca fluviatilis, two species taken frequently by the otter in the River Lee catchment. All relationships yielded significant linear equations, whereas those for bone vs. body weight were logarithmic. Regression slopes for head bones do not differ greatly within species but do across species of the same family.
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.
Fecundity and growth allocation to reproduction were investigated in stream-dwelling threespine Gasterosteus aculeatus L. (leiurus) and ninespine Pungitius pungitius (L.) sticklebacks of St. Ippollitts Brook, Hertfordshire (England), between August 1993 and October 1994. We compared oocyte size distributions as well as the relative fecundity of females containing mature oocytes, compared growth allocation to gonadal growth and overall reproductive allocation from estimates of total egg supply, the number of reserve oocytes eventually spawned, the proportion of reserve oocytes not spawned, the total number of oocytes spawned, and the number of egg clutches per season. Notable differences in reproductive strategy were observed between the two species. Ninespine sticklebacks were smaller in size than threespine, but compensated for this through a smaller size at first maturity, an almost equal seasonal fecundity (number of spawned oocytes) accompanied by a higher number of unspawned oocytes (i.e. maintenance of a low mature-to-total oocyte ratio), an extended spawning period, a higher number of clutches, and an overall lower reproductive allocation.
A total of 79 females of spirlin Alburnoides bipunctatus from the Rudava stream (small lowland stream, Western Slovakia) were examined to obtain data on fecundity and annual oocyte development cycle. Within spawning season (mid- April to early July), the reproduction resources seemed to be allocated in its former half more intensively (more yolked eggs present in ovaries compared to the rest of spawning season). For the mean SL = 76 mm and eviscerated body weight = 7.2 g, mean absolute fecundity of females in pre-spawning phase (n=13) was 3020 eggs (SD = 923; 2695 yolked eggs, SD = 1054), and mean relative fecundity 430 eggs/g (SD = 81; 373 yolked eggs, SD = 100). Number of eggs in the right and the left ovary differed significantly in 63.3 % of females, with a maximum difference of 1405 eggs. Two clues, namely 1) no gap in distribution between immature, unyolked oocytes (present in an ovary throughout the whole year), and yolked (vitellogenic) oocytes, 2) no increase in mean diameter of yolked oocytes towards the end of spawning season, suggest that spirlin is a species with indeterminate fecundity.
Microhabitat use in the endangered cyprinid species spirlin Alburnoides bipunctatus and accompanying species was examined in three water courses of Slovakia to determine the species’ environmental requirements as a basis for informing conservation policy and management. In all three rivers, water velocity, water depth and substratum character were central features of spirlin microhabitat use, regardless of year or season of sampling, with only limited variation in microhabitat associations as a function of time of day. Clear differences in microhabitat use and intra-specific associations during development were observed in two of the rivers. In particular, a shift in velocity preference towards faster flowing waters appears characteristic of spirlin during their larval and juvenile development, and possibly also that of gudgeon Gobio gobio, European minnow Phoxinus phoxinus, and chub Leuciscus cephalus, which are all species that may be significantly associated with young spirlin. Disproportionate use of deeper waters tended to increase with age in spirlin, and in gudgeon and barbel Barbus barbus, but spirlin preference for substratum was less uniform, with affinities ranging from indifference to strong preference. This contrasts the clear preferences for sand in gudgeon and for cobbles in European bullhead Cottus gobio. Of particular importance to young-of-the-year (YOY) spirlin are lentic zones with some sort of ligneous debris – habitat also used by YOY gudgeon and minnow. Contrary to previous reports elsewhere, spirlin did not avoid in-stream vegetation where present, and in one river it was preferred by YOY and 1+ spirlin. To avoid declines in spirlin and accompanying stream-dwelling species, such as reported elsewhere in Europe, river management in water courses such as these should be limited to the rehabilitation of regulated sections to achieve a natural, heterogeneous channel character.
The tubenose goby has been reported to be the first non-native postglacial gobiid immigrant from the Lower Danube refuges. It is thus a pioneer species that was the forerunner of the extensive invasion of Ponto-Caspian gobies that ascended the River Danube and spread across Europe a century before other goby species. It appears that recently the tubenose goby invasion has accelerated. In this paper historical data on the distribution of the tubenose goby, together with data from extensive monitoring of fish communities in Slovakia are examined to evaluate both the temporal and spatial aspects of tubenose goby distribution dynamics. Until the 1990s, the species was recorded only in the River Danube and small water bodies in the Danubian Lowland (Slovakia). Since then the tubenose goby has spread upstream into tributaries of the River Danube. It was also recorded in several streams in eastern Slovakia after 2014, and the spatial data demonstrate that the tubenose goby has been colonising new water bodies, progressing to the north and ascending rivers, reaching higher altitudes than previously reported. These findings suggest that the tubenose goby deserves attention, even after two centuries following the onset of its invasion, and its further expansion across Europe should be carefully monitored.