Gudgeon- Two New Additions to Britain's Freshwater Fishes

Sunbleak and Topmouth Gudgeon- two new additions to Britain's freshwater fishes ~ ~ Topmouth Gudgeon Sunbleak Adrian C Pinder and Rodolphe E Gozlan hroughout the world, it is commonly Globally, among vertebrates, introductions of accepted that the introduction of new freshwater fish species have been among the most T species to a stable ecosystem can upset the numerous (Crivelli 1995), and the introduction of environment and the species already present. non~native fishes to the UK is not a new phenome- Aquatic ecosystems are no exception and, with a non. The Carp Cyprinus carpio was first intro- dramatic increase in world travel and trading over duced for aquaculture in the 15th century (Balon the last century, are increasingly at risk from 1995), and during more recent times introductions biological invasion. that have successfully colonised UK watercourses The various threats posed by the introduction of include the Ide Leuciscus idus, Bitterling Rhodeus alien species are many and can manifest them- sericieus, Zander Sander lucioperca and Pumpkin- selves in the form of direct predation on native seed Lepomis gibbosus. The motives responsible species, competition for food, introduction of new for these introductions vary from ornamental fish- diseases or parasites, or potential to cause change keeping and angling interest to, in the case of to the environment. Grass Carp Ctenopharyngodon idella, their use as December 2003 British Wildlife 77 Sunbleak and Topmouth Gudgeon a biological herbicide to control the excessIve Whereas most British freshwater fish grow rela- growth of aquatic weed. tively rapidly for the first few years, until they become sexually mature, in Sunbleak growth is Sunbleakand Topmouth Gudgeon most rapid during the first summer, beyond which This article highlights two of the most recent intro- energy reserves are reallocated from somatic ductions to the fish fauna of Great Britain: growth towards gonad production, resulting in Topmouth Gudgeon Pseudorasbora parva and Sunbleak becoming sexually mature at one year Sunbleak Leucaspius delineatus. Over the last three old (Gozlan et al. 2003a). years, various aspects of the biology and ecology, During spawning, males, which are smaller than including the reproductive behaviour, habitat females, take up territories around the stems and requirements and early development, and the distri- underside of the leaves of water-lilies and other bution of these two species have been studied by the flat-surfaced structures. The males then clean any authors at the Centre for Ecology and Hydrology in accumulated bio-films from the spawning Dorset. Here, we summarise their fascinating life substrate, using their mouths. The ripe females, histories and assess the current status of these new which develop swollen, distended ovipositors additions to the British aquatic fauna. We also during spawning, join the male and travel at high discuss the future of these species in Britain and the speed across the spawning substrate (Gozlan et al. risks that they pose to our native fishes. 2003b), depositing strips of up to 80 highly adhesive eggs. A female Sunbleak can typically deposit a Basicbiology strip of 40 eggs in less than one second. After the Both Sunbleak and Topmouth Gudgeon are small female has spawned, the male guards the eggs and cyprinids possessing highly developed life-history encourages other females to deposit their eggs at strategies which have undoubtedly assisted them the same nest site. The male then guards the eggs in successfully colonising bodies of water in the until they hatch, which takes approximately four British Isles. The majority of cyprinid species take days at noc (Pinder & Gozlan in press). 2-4 years to become sexually mature and spawn In contrast to its alien and invasive status in the just once a year. The females scatter many thou- UK, the Sunbleak is considered rare or vulnerable sands of eggs over aquatic macrophytes or gravel, throughout much of its native range (Lelek 1987). and these are then left unguarded and vulnerable It is also listed as protected under Appendix III of to predation. Unusually for cyprinids, both the Bern Convention. Sunbleak and Topmouth Gudgeon become sexually mature at one year old and are batch spawn- TopmouthGudgeon ers, with females laying several batches of eggs, Rarely attaining 8cm in length or living for more between April and July, which are guarded by the than three years, Topmouth Gudgeon predomi- males until they hatch. nantly occupy the bentho-pelagic zone, where This combination of attributes means that a their diet consists of algae, benthic invertebrates, relatively low number of eggs (when compared zooplankton, molluscs and also the eggs and with other cyprinid species) are produced, but larvae of other fish species (Xie et al. 2000). As with the parental care ensuring higher than aver- opportunistic feeders, Topmouth Gudgeon will age hatching rates. Also, as the brood is spread also take food from the )'Vater's surface, where across an extended period, larvae are less vulnera- feeding on terrestrial insects and other floating ble to changes in environmental conditions, thus objects is accompanied by an audible clicking enhancing survival rates (Gozlan et al. 2003a). noise. This behaviour is responsible for these fish being referred to by some as 'clicker barbs'. Sunbleak Topmouth Gudgeon have many life-history char- Sunbleak closely resemble Bleak Alburnus alburnus acteristics in common with Sunbleak. However, in appearance, but are a smaller species not exceed- subtle differences are evident. In contrast to ing 8cm in length and rarely living for more than Sunbleak, male Topmouth Gudgeon are larger than three to four years. They are gregarious and live in the females and exhibit secondary sexual character- large shoals close to the water's surface, where they istics such as tubercles around the mouth, and the typically feed on zooplankton and terrestrial insects. body coloration becomes much darker, particularly 78 British Wildlife December 2003 Sunbleak and Topmouth Gudgeon on the fins. At this time, territories are established which are defended aggressively by the males. Spawning substrata have previously been reported to include the underside of rocks and broadleaved floating macrophytes. Our studies have shown that, like Sunbleak, Topmouth Gudgeon can successfully spawn on any flat-surfaced object, although they show a preference for structures with a cavity, which are easier to guard from other fish, including their own speCIes. Preliminary investigations into the spawning behaviour, carried out by the Identification authors, suggest that bigger males are most successful in defending territories from Sunbleak conspecifics and in attracting gravid females. This Olive-green back, silver sides and abdomen with iridescent blue sheen along flanks is in agreement with the findings of Katano & Anal fin rays111/10-13 Maekawa (1997), who stated that females choose Distinctly short lateral line terminating before dorsal fin males with larger body size as their mates. Females Upturned mouth will spawn with several different males in a day, Topmouth Gudgeon depositing several batches of eggs in each terri- 34-38 lateral scales with dark edges tory. Dark band of lateral pigment (often absent in larger The eggs of Topmouth Gudgeon superficially (>Scm) individuals) resemble those of the Sunbleak, but have a thicker Dorsal and anal fins strongly convex Upturned mouth chorion and are encased in a jelly-like substance which is highly adhesive. Eggs are released in In the winter the shoals disperse to deeper water. smaller batches than those of Sunbleak, usually Sunbleak prefer slow-flowing rivers and associ- four to ten at a time. The male guards the eggs ated backwaters, drains, canals and stillwaters, until they hatch. The incubation period of the eggs although fast-flowing rivers have previously been is approximately seven days at 20Ce. Katano & identified as conduits for dispersal. Maekawa (1997) recorded mean fecundity as 1,049 eggs per female, with a maximum of 6,285. Topmouth Gudgeon Internationally, Topmouth Gudgeon are During early development, Topmouth Gudgeon regarded as a highly invasive pest species. disperse from the nest site to the benthos, where they hide between and under stones. It is not until Habitat all the fins are completely formed that they can be Sunbleak found in the open water of shallow marginal habi- During the first few weeks of development, tats. Topmouth Gudgeon are not a closely shoal- Sunbleak are found in shallow marginal habitats ing species and spread themselves across a broad where water temperatures are generally higher, range of the habitat types available to them. They supporting blooms of zooplankton and facilitat- are less specific than Sunbleak in terms of habitat ing optimum growth conditions. As the larvae choice and can thrive in streams, rivers and still- become more developed (around 40 days), these waters, although they are reported to favour shal- marginal habitats are abandoned in favour of deep low, still or slow-running waterbodies, water away from the banks. Here, they form preferentially with macrophyte beds (Adamek et shoals, swimming just below the water's surface. al. 1996). December 2003 British Wildlife 79 Sunbleak and Topmouth Gudgeon Distributionand currentstatus in the UK d --~ £LV,",". ~'\. N Figure 1 Present f!;. \J /" The original importation of both species is I~-, ' ) +I distributionSunbleak (black)of I /j~ \ believed to have occurred during the mid-1980s ,~ , h~ 'I. "-. and Topmouth through an ornamental-fish supplier near ;V j) \c;. \ Gudgeon (grey) Romsey, in Hampshire. Figure 1 shows an up-to- } ~ ~ in the UK.The date distribution map for both species and the ~. \ arrow shows only known site of introduction to the DK. ~ . Zr-~ the location of ..\><,..>) J i the original Sunbleak :( I ; importation of ~~I~L ~- both species, Originating from continental Europe and Russia, [F~-.""'" ... -/ ~'J although Sunbleak are well distributed from the Caspian j/ ]~._~ Sunbleak are no Sea to the North Sea and from the Volga to the c<,""~ atlongerthis site.present Alps and Pyrenees.

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