Growth and reproduction of introduced goldfish Carassius auratus in small ponds of southeast England with and without native crucian carp Carassius carassius

Abstract

The ornamental Asiatic species, goldfish Carassius auratus, was introduced to open waters of the UK in the late 17th century. The species reproduces readily in small ponds and threatens native species, in particular crucian carp Carassius carassius, but surprisingly there are no known published studies on the growth and reproduction of feral pond populations of this species in the UK and relatively few elsewhere. The aim of the present study was to assess the growth (back-calculated length at age), body condition and reproduction (fecundity, egg size, length and age at maturity) of goldfish living in small ponds of Epping Forest (northeast London, England), either alone (allopatry) or with (sympatry) native crucian carp, in order to provide the necessary background information to inform the risk assessment of this non-native fish species. Growth increments in the allopatric goldfish populations were similar, with progressively declining growth increments with increasing age. This contrasts with goldfish living in sympatry with crucian carp Carassius carassius, where growth increments remained high for ages 1–2, 2–3 and 3–4. Body condition values varied little, but goldfish living in allopatry had significantly greater condition than those living in sympatry with crucian carp. Sexual maturity was achieved by at least some age 1+ fish in all populations, with young mean ages (1.0–1.7 years) and short mean standard lengths (50.0–63.4 mm SL) at maturity in females relative to an introduced population in Italy (2.1 years and 139.2 mm SL, respectively). The results are discussed within the context of life-history theory.