The relation between length (L) and weight (W) was estimated for 32 species representing 12 families of fishes from six water resources in the Marmara region, Turkey. The parameter b ranged from 2.66 to 3.56. For 12 species length-weight relationships were not previously available.

Host-parasite relationships are often characterized by the rapid evolution of parasite adaptations to exploit their host, and counteradaptations in the host to avoid the costs imposed by parasitism. Hence, the current coevolutionary state between a parasite and its hosts is predicted to vary according to the history of sympatry and local abundance of interacting species. We compared a unique reciprocal coevolutionary relationship of a fish, the European bitterling (Rhodeus amarus) and freshwater mussels (Unionidae) between areas of recent (Central Europe) and ancient (Turkey) sympatry. Bitterling parasitize freshwater mussels by laying their eggs in the gills of mussel and, in turn, mussel larvae (glochidia) parasitize the fish. We found that all bitterling from both regions avoided one mussel species. Preferences among other mussel species tended to be related to local mussel abundance rather than duration of sympatry. Individual fish were not consistent in their oviposition choices, precluding the evolution of host-specific lineages. Mussels were demonstrated to have evolved strong defenses to bitterling parasitism in the area of ancient sympatry, but have no such defenses in the large areas of Europe where bitterling are currently invasive. Bitterling avoided glochidia infection irrespective of the duration of sympatry. K E Y W O R D S :Coevolutionary arm races, evolutionary lag, gentes, host race, specialization, symbiosis.

The underlying mechanisms responsible for ecological plasticity and consequent invasive character of non‐native freshwater fish species, variations in growth and life history traits in gibel carp Carassius gibelio (Bloch) were compared in natural and artificial water bodies of Turkey. Females significantly outnumbered males in all natural and most artificial waters. Discriminate function analysis differentiated gibel populations into three separate groups (natural lakes, artificial water bodies and running waters), with significant differences among separated groups in growth index, standard length and age at maturity, relative fecundity and gonado‐somatic index, but not in egg diameter and both generalised and relative condition. Growth features (e.g. growth index and relative condition) and reproductive features (e.g. relative and absolute fecundity) positively correlated with water body area. No correlations were found for any growth or life history trait with depth, latitude and altitude. With the exception of smaller size at maturity, all traits were higher in populations from artificial water bodies than those inhabiting running waters, suggesting gibel carp is required to exert more reproductive effort to invade natural ecosystems than artificial waters.

1. In response to reported declines in crucian carp Carassius carassius across Europe, studies of the status and population biology of the species in England led to Biodiversity Action Plan priority designation in the eastern county of Norfolk.2. In light of new data on crucian carp populations in eastern England (counties of Essex, Hertfordshire and Norfolk), a comprehensive review of available information throughout its native and introduced European range was undertaken to assess the growth and reproduction at a broader scale, thus contributing to conservation and management strategies at a country scale in the UK.3. For all populations, mean sex ratio was 1:1, back-calculated total length (TL) ranged from 19 to 334 mm, and maximum age was 13 years. Growth and body condition varied greatly across Europe. Growth trajectories in England, Russia and Poland were significantly faster than in Finland. Within England, growth index was lower in Hertfordshire than in Essex and Norfolk, and Fulton condition (plumpness) index was higher in Essex than in Norfolk. 4. Reproductive traits varied greatly both in males and females, with age at maturity ranging from 1.5 to 5 years, and with the shortest life spans observed in England. Length at maturity was usually at a lower TL in males than females (except in Essex populations). Female age at maturity decreased significantly with juvenile growth, which was defined as TL at age 2, the age above which females in most populations achieved maturity.5. Predicted temperature rise (i.e. under a climate change scenario) may benefit crucian carp growth, as predicted for related competitive invaders (e.g. goldfish Carassius auratus). From a conservation perspective, suggested management strategies include reducing populations of non-native fishes, implementing measures of habitat restoration and re-stocking rehabilitated ponds from 'source areas', i.e. those containing crucian carp populations in good status.

Gibel carp, Carassius gibelio (Bloch), impacts on native fish species have been reported but little studied despite a long history of introductions in Europe. This species is able to reproduce gynogenetically, which involves the use of sperm from males of other species to activate egg development, so reproductive competition is a likely but virtually unstudied impact of gibel carp on native fishes. This study evaluates the impact of introduced C. gibelio on the population biology of native fishes over a 6‐year period in a mesotrophic drinking water reservoir in north‐western Turkey. A dramatic decrease in the relative density (i.e. catch per unit effort) of native species correlated significantly with an increase in C. gibelio relative density. Growth characteristics (back‐calculated ages, growth index and relative condition) and length at maturity did not differ significantly among years in C. gibelio and native fishes. Relative density, duration of spawning, reproductive effort and gonado‐somatic index of C. gibelio increased with some water quality variables [total phosphorus (TP); chlorophyll‐a (Chl‐a)] and coincided with decreasing trends for natives. However, TP and Chl‐a were not correlated with growth features in C. gibelio or natives fishes. The results suggest that the decline in the reservoir’s native cyprinid populations is likely due to a combination of degrading environmental conditions and a disparity in reproductive effort, with introduced C. gibelio invasion facilitated by gynogenetic reproduction and an observed interference with native fishes during spawning.

Gracilaria vermiculophylla, a red macroalga from the West Pacific, was discovered in western Germany (the Wadden Sea) in 2002 and has since also been observed in Sweden (from about 70 km south to about 80 km north of Göteborg), Denmark (Wadden Sea, Horsens Fjord, Limfjorden, Vejle Fjord, Holckenhavn Fjord, Øster Hurup Harbor) and eastern Germany (Kiel Bay). Today, less than 5 years following its first observation in the Wadden Sea the invader is common in many invaded regions, often being amongst the most abundant macroalgal species. G. vermiculophylla is successful in shallow protected soft-bottom estuaries and bays, typically in association with ubiquitous native invertebrates (lugworms, tube-building worms, mussels, cockles, snails). The invertebrates provide substratum for holdfast attachment and thalli incorporation, most likely increasing the stability of local G. vermiculophylla populations. We hypothesize that this substratum provision is highly important for its general invasion success. We also confirm that G. vermiculophylla can maintain growth at all salinities experienced along Danish coastlines (8.5-34 psu). In addition, laboratory experiments indicate that the ubiquitous grazer Littorina littorea has the potential to control G. vermiculophylla growth under specific environmental conditions, but also that L. littorea may facilitate small-scale dispersal within invaded locations, because grazing increases thalli fragmentation rates. Given its widespread distribution, rapid range expansion, and known ecological traits, G. vermiculophylla is clearly a permanent resident of northern European waters.

Scale samples from crucian carp, Carassius carassius (L.), collected over a 10-year period from a population in an ornamental pond were used to examine patterns in growth as a function of environmental factors, including water temperatures. Back-calculated standard lengths (SL) at age differed between year classes in most cases. Annual SL increments were related to temperature and age using a non-linear growth model. Growth declined with increasing age, whereas annual SL increments increased with increasing water temperature. The best-fit model was with the total number of summer days when air temperature exceeded 20°C (using water temperature equivalents of air temperature). A growth model including water temperature, age, year class, relative condition and rainfall was a better fit than other models. Year-class strength was positively correlated with water degree-days, and year-class strength negatively affected annual SL increments. The results indicate that within a strong year class of crucian carp, the growth of individual fish is reduced compared with weak year classes, suggesting that density negatively affects growth in ponds where resources are limited. K E Y W O R D S : conservation, native species, non-linear growth, water temperature.

Summary Length–weight relationships were calculated for nine freshwater fish species belonging to two families using 1020 specimens from 15 water sources in the western part of Anatolia, Turkey. This study is the first reference on length–parameters for these species, eight of which are endemic, and with new maximum length records for three of the species.