A review and meta-analysis of growth and life-history traits of a declining European freshwater fish, crucian carp Carassius carassius

Abstract

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 334mm, and maximum age was 13years. 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 5years, 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.