Ex-situ breeding of native unionids in Lake Banyoles (Spain) as part of a LIFE project

Abstract

Lake Banyoles is the second largest natural lake in the Iberian Peninsula and is one of the first places in the Iberian Peninsula where massive planned fish introductions have taken place. The proliferation of alien fish species explains the current scarcity of the native species that are the natural hosts of the parasitic larvae of unionids. This situation has led to a dramatic regression in the four native unionid species found in this lake (Unio mancus, U. ravoisieri, Potomida littoralis and Anodonta anatina). As a result of management geared towards the preservation of natural heritage, the ecological quality of this site has improved in recent decades. However, the main challenge for the management of the lake and its surrounding areas is now posed by invasive alien species. Projecte Estany (LIFE 08/NAT/E/000078) was a four-year project (2010–2013) whose main aim was to design and implement a large-scale intervention actions that would combat, slow down and revert the decline in species and habitats of Community Interest via (1) the control of invasive alien species, (2) the strengthening of populations of seriously threatened native species, and (3) the restoration of key patches of riparian habitats. As part of the project to recover populations of two Unio species, a breeding laboratory was set up. During the first years of the project, several methodologies were tested to obtain mussel glochidia (larvae), optimize fish infection and design a methodology for fattening juveniles. Up to three different native fish species were tested as hosts for local Unio larvae: Barbus meridionalis, Squalius laietanus and Salaria fluviatilis. All demonstrated their capacity to act as hosts and release viable juveniles; however, due to their larger size, only the first two species are used for intensive mussel breeding, along with Luciobarbus graellsii. Between 2011 and 2013, a total of 108,875 U. mancus and 27,423 U. ravoisieri juveniles were produced via the artificial infection of host fish with larvae grown in a number of semi-natural sequential breeding systems fed by water and sediment from their natural habitats, pools, plastic outdoor channels, and/or cages. In the tested systems, U. mancus reached a mean length of 9.7 mm (SD_1.53) in one year and 12.4 mm (SD_1.55) in two years; for U. ravoisieri these values were 15.8 (SD_0.76) and 21.2 mm (SD_2.45). In the context of the further four years (2014-17) allotted to the project (LIFE Potamo Fauna, LIFE12 NAT/ES/001091), efforts to breed Unio species in this laboratory, which has been enlarged, will continue. We will describe the results of the different juveniles’ collection systems and the facilities created to improve their growth over the past six years. The protocols implemented, the current installations and the results of the captive breeding of Unio species are shown here.