First evidence of bighead carp wild recruitment in Western Europe, and its relation to hydrology and temperature

Abstract

Bighead carp (Hypophthalmichthys nobilis) have been introduced throughout Europe, mostly unintentionally, and little attention has been given to their potential for natural reproduction. We investigated the presence of young-of-the-year bighead carp in an irrigation canal network of Northern Italy and the environmental conditions associated with spawning in 2011–2015. The adult bighead carp population of the canal network was composed by large, likely mature, individuals with an average density of 45.2 kg/ha (over 10 fold more than in the main river). The 29 juvenile bighead carp found were 7.4–13.1 cm long (TL) and weighed 9.5–12.7 g. Using otolith-derived spawning dates we estimated that these juveniles were 94–100 days old, placing their fertilization and hatch dates in mid-to-end-June. Using this information in combination with thermal and hydraulic data, we examined the validity of existing models predicting the onset of spawning conditions and the viability of egg pathways to elucidate spawning location of the species. While evidence of reproduction was not found every year, we determined that potentially viable spawning conditions (annual degree-days and temperature thresholds) and pathways of egg drift suitable for hatching are present in short, slow-flowing canals.

Exotic species invasions undermine regional functional diversity of freshwater fish

“…Conversely, urbanization and intensive agriculture, causing high nutrient loads and consequent eutrophication, are the main factors affecting lowland rivers 10 . A network of drainage canals was established in the lowlands to support agricultural irrigation around the 19 th century, with hydrological management aimed at supplying both irrigation and drainage needs 10,47 . The study area was in a late invasion stage 11 at the time of sampling, since loss of native species and exotic invasion occurred already prior to 1997 10 , before the data analyzed here were collected.…”

Long-term fish monitoring underlines a rising tide of temperature tolerant, rheophilic, benthivore and generalist exotics, irrespective of hydrological conditions

“…However, due to the hydraulics of the siphons at Berra basin, some of these exotic fish have not been recorded in our data. Hypophtalmichthys spp., two pelagic planktivores present in the Po River and in the canal network (Milardi et al, 2017), were not captured. This is probably due to their very low density in the Po River and to their more epipelagic habits (Kolar et al, 2007), while the siphons draw water from a deeper water layer.…”

Fisheries Volume 43 Number 7 July 2018

“…In North America, the term "Asian carp" is a category often applied to a suite of four fi sh species that are native to large rivers of China and Russia: Bighead Carp Hypophthalmichthys nobilis , Black Carp Mylopharyngodon piceus , Grass Carp Ctenopharyngodon idella , and Silver Carp H. molitrix . These species have detrimental ecological effects on North American and European river and lake ecosystems (Irons et al 2007 ;Haupt and Phelps 2016 ;Milardi et al 2017 ), and as such, they are considered invasive species to be eradicated or reduced to much lower population levels. Conversely, these species have been raised in aquaculture in China for centuries, and they hold a revered place in Chinese human culture and history.…”