Global patterns and clines in the growth of common carp Cyprinus carpio.

This review provides a meta-analytical assessment of the global patterns and clines in the growth of Cyprinus carpio as measured by length-at-age (Lt ) or von Bertalanffy growth function (VBGF) parameters, mass-length relationship (W-Lt ) and condition factor, based on literature data. In total, 284 studies were retrieved spanning 91 years of research and carried out on 381 waterbodies-locations in 50 countries in all five continents. Although native C. carpio achieved larger (asymptotic) size relative to its non-native counterpart, the latter grew faster during the first 7 years of life. Lentic populations (especially in natural lakes) also achieved larger sizes relative to lotic ones and the same was true for populations in cold and temperate v. arid climates. Unlike previous studies (on much more restricted datasets), only weak latitudinal clines in instantaneous growth rate, Lt at age 3 and mortality were observed globally and this was probably due to the presence of counter-gradient growth variation at all representative age classes (i.e. 1-10 years). Slightly negative allometry was revealed by the W-Lt and the related form factor tended to distinguish the more elongated and torpedo-shaped body typical of the wild form from the deeper body of feral-domesticated C. carpio. Existing population dynamics models for C. carpio will benefit from the comprehensive range of waterbody type × climate class-specific VBGF parameters provided in the present study; whereas, more studies are needed on the species' growth in tropical regions and to unravel the possibility of confounding effects on age estimation due to both historical and methodological reasons.

Laboratory and field validation of a simple method for detecting four species of non-native freshwater fish using eDNA.

This paper presents the first phase in the development and validation of a simple and reliable environmental (e)DNA method using conventional PCR to detect four species of non-native freshwater fish: pumpkinseed Lepomis gibbosus, sunbleak Leucaspius delineatus, fathead minnow Pimephales promelas and topmouth gudgeon Pseudorasbora parva. The efficacy of the approach was demonstrated in indoor tank (44 l) trials in which all four species were detected within 24 h. Validation was through two field trials, in which L. gibbosus was detected 6-12 h after its introduction into outdoor experimental ponds and P. parva was successfully detected in disused fish rearing ponds where the species was known to exist. Thus, the filtration of small (30 ml) volumes of pond water was sufficient to capture fish eDNA and the approach emphasised the importance of taking multiple water samples of sufficient spatial coverage for detecting species of random or patchy distribution.

Morphological variability of black bullhead Ameiurus melas in four non-native European populations.

External morphology in black bullhead Ameiurus melas, a fish species considered to have high invasive potential, was studied in its four non-native European populations (British, French, Italian and Slovak). The aim of this study was to examine this species' variability in external morphology, including ontogenetic context, and to evaluate its invasive potential. Specimens from all non-native populations reached smaller body size compared to individuals from native populations. Juvenile A. melas were found to have a relatively uniform body shape regardless of the population's origin, whereas adults developed different phenotypes depending upon location. Specimens from the U.K., Slovak and French populations appeared to be rather similar to each other, whereas the Italian population showed the most distant phenotype. This probably results from the different thermal regime in the Italian habitat. Ameiurus melas from non-native European populations examined in this study showed some potential to alter the body shape both within and between populations. The phenotypic plasticity of A. melas, however, was not found to be as significant as in other invasive fish species. The results suggest that morphological variability itself is not necessarily essential for invasive success. The invasiveness of A. melas is therefore probably favoured by variations in its life-history traits and reproduction variables, together with some behavioural traits (e.g. voracious feeding and parental care) rather than by phenotypic plasticity expressed in external morphology.

Interstitial movement and emergence of barbel Barbus barbus free embryos and larvae.

The movement of barbel Barbus barbus free embryos in the interstitial zone and the timing of larval emergence were studied for 12 days in an artificial stream. After egg fertilization (day 1), hatching occurred on day 6, downstream interstitial movements of free embryos on day 9 and emergence and downstream movement of all larvae on day 12, with density of free embryos decreasing as day of emergence approached. The results suggest that a memory-based response of B. barbus to environmental conditions, previously observed in 0+ year juveniles, begins at an early age.

Heated competition: how climate change will affect non-native pumpkinseed Lepomis gibbosus and native perch Perca fluviatilis interactions in the U.K.

Heated and ambient temperature experimental ponds were used to examine competition between introduced pumpkinseed Lepomis gibbosus and native perch Perca fluviatilis in England, U.K., and how these interactions are likely to change under climate warming conditions. Results from three sets of two-week experiments indicated that in both species and in all sets, growth was faster in heated than in ambient temperature ponds. Growth of both P. fluviatilis and L. gibbosus in sympatry did not differ significantly from that observed in allopatric ponds. Diet analysis indicated that increased resource partitioning occurred when P. fluviatilis and L. gibbosus were reared in sympatry, with P. fluviatilis shifting to a diet higher in microcrustaceans. The results do not support the previous claims of adverse effects of L. gibbosus on P. fluviatilis populations. Under conditions of climate change, however, which have been demonstrated experimentally to enhance L. gibbosus recruitment, this species is expected to become invasive in England, resulting in higher densities that may exert a stronger competitive effect than examined in this study.

Towards the conservation of crucian carp Carassius carassius: understanding the extent and causes of decline within part of its native English range.

The extent and causes of crucian carp Carassius carassius decline were assessed during an initial study of c. 25 ponds in north Norfolk, eastern England, U.K., which was then replicated (a validation study) on another c. 25 ponds in an adjacent area. Of these ponds, c. 40 are known to have contained C. carassius during the 1970s-1980s. In the initial and validation studies, C. carassius were found in only 11 of these ponds, yielding declines of 76% (five of 21 ponds) and 68% (six of 19 ponds), respectively (72% decline overall). Non-native cyprinids, including goldfish Carassius auratus and common carp Cyprinus carpio and their hybrids with C. carassius, were observed in 20% of the ponds. Causes of C. carassius local extinction from 21 ponds were confidently determined as desiccation due to drought, terrestrialization and habitat deterioration, hybridization and competition with non-native cyprinids, agricultural land reclamation and predation (after the introduction of pike Esox lucius). This study led to C. carassius being designated as a Biodiversity Action Plan (BAP) species in the county of Norfolk, the first formal conservation designation for the species in the U.K. The C. carassius BAP plan aims to halt the decline of this much overlooked species through reintroductions and selective stocking of suitable ponds within the native range of the species.

The effect of elevated temperature on spawning of introduced pumpkinseed Lepomis gibbosus in Europe.

In an experimental comparison of pumpkinseed Lepomis gibbosus reproduction under ambient and climate change water temperature regimes, spawning occurred earlier in the season, which is likely to lead to greater young-of-the-year survival with concomitant implications in the U.K. under warmer climatic conditions.

Morphological variability of the Asiatic cyprinid, topmouth gudgeon Pseudorasbora parva, in its introduced European range.

To assess the spatial variability in external morphology of non-native populations of topmouth gudgeon Pseudorasbora parva within an ontogenetic context, triple regression analysis (distance-based measurements) was applied to data from eight European populations (two Slovak, four Romanian, one English and one French). The data from Slovakia were also subjected to geometrical analysis (co-ordinates-based measurements) to obtain a more complex picture of the species' overall morphology. Great phenotypic variability was observed, being expressed not only in the formation of different definite phenotypes but also in the manner by which the phenotypes are achieved. Thus, both the definite phenotype and the patterns of development in invasive P. parva may be highly influenced by environmental conditions. Such great morphological (phenotypic) variability is likely to be one of the attributes that make this species such a successful invader.

Long-term recovery of macrobenthos and fish assemblages after water pollution abatement measures in the River Petite Baïse (France).

Riverine ecosystems are subject to a large variety of man-made influences, and in recent years a new public awareness of the need to protect rivers has emerged within the industrialized world. The present study focuses on the effect of abatement of pollution from one factory on the recovery of fish and macroinvertebrate species richness in the River Petite Baïse over a 20-year period (1973-1993). Until 1973, the Petite Baïse (75 km in length) received not only factory waste (nitrogenous rich effluents) but also the untreated sewage of many villages and agricultural runoff from the river's catchment. In 1970, macroinvertebrates and fishes were absent in the river despite having initially been classified as of the barbel Barbus barbus zone, and extensive efforts were made by the factory to reduce pollution to allow the riverine community to recover. Regular surveys between 1973 and 1993 revealed a progressive improvement in water quality and the recolonization of the river by macrobenthic and fish populations. Macrobenthic fauna species richness gradually increased from zero in 1970 to level 8 or 9 in 1993 (Verneaux and Tuffery method), reflecting improvements in river water quality. Fish were not observed until 40 km downstream of the factory in 1978, 16 km in 1980, and approximately 5 km by 1990. Fish species richness increased from five in 1978 (barbel, chub Leuciscus cephalus, stone loach Barbatula barbatula, minnow Phoxinus phoxinus, gudgeon Gobio gobio) to eight in 1990 (the carnivorous brown trout Salmo fario, the omnivorous chub, and six benthophagous fishes: gudgeon, barbel, minnow, stone loach, sofie Chondrostoma toxostoma, carp Cyprinus carpio). Fish biomass 45 km downstream the factory increased from 1 g/m2 in 1978 to more than 5 g/m2 by 1990. Recolonization of the river, in particular those areas furthest downstream from the factory, occurred as a result of reductions in the nitrogen inputs emanating from the factory.

Stability and performance of mesophilic anaerobic fixed-film reactors during organic overloading.

The stability of downflow stationary fixed-film (DSFF) reactors was evaluated under extreme organic shock loads. Reactors could handle five- to sevenfold increases in organic loading and recover to normal performance in a relatively short period of time (usually 24-72 h) during treatment of well-buffered sucrose and acetic acid wastewater at 27 and 35 degrees C. Overloading was characterized by elevated volatile-acid concentrations, decreased reactor pH, and excess biofilm sloughing. Reactors could not cope with extreme organic shocks during treatment of poorly buffered sucrose wastewater. The pH of the mixed liquor was observed to be a more important factor than the volatile-acid concentration in determining whether DSFF reactors would recover in a reasonable period of time.