Native and exotic fishes in a Patagonian reservoir with rainbow trout cage culture: spatial and trophic resource use

Abstract

-Although the interactions of exotic salmonids with native Patagonian fishes are well known, little is known about the ecology and impact of farmed fish escapees. Salmonid production in Argentina is largely concentrated in the Alicurá reservoir in north Patagonia, where fish community studies have been scarce. Here, we assess and compare the spatial distribution, body size-condition and diet of the different fish species in this reservoir. Strong vertical segregation was observed between exotic rainbow trout Oncorhynchus mykiss (both escapees and wild), dominating the littoral zone, and native Percichthys trucha which dominate the medium and deep strata. Low piscivory-benthivory and high zooplanktivory were observed for rainbow trout, both traits being uncommon at a regional scale. Escaped farmed rainbow trout (ERT) diet included abundant indigestible items along with wild prey. Higher body condition of P. trucha close to farms, as well as the regionally unprecedented high incidence of Daphnia sp. in the guts of all the species suggest that farm nutrient discharges have had significant impacts. Finally, the high body condition of ERT, together with their wild food diet and the long dispersal distance observed, demonstrate post-escape success, drawing our attention to potential upstream dispersion affecting the biodiversity and fisheries of Patagonian rivers and lakes.Keywords: aquaculture impact / freshwater salmonid / niche segregation / diet / Patagonia Résumé -Poissons indigènes et exotiques dans un réservoir de Patagonie avec aquaculture en cage de truites arc-en-ciel : utilisation des ressources spatiales et trophiques. Bien que les interactions des salmonidés exotiques avec les poissons patagoniens indigènes soient bien connues, on connaît peu l'écologie et l'impact des poissons échappés d'élevage. La production de salmonidés en Argentine est largement concentrée dans le réservoir d'Alicurá dans le nord de la Patagonie, où les études sur les communautés de poissons ont été rares. Ici, nous évaluons et comparons la répartition spatiale, la taille du corps et l'alimentation des différentes espèces de poissons dans ce réservoir. Une ségrégation verticale forte a été observée entre la truite arc-en-ciel exotique Oncorhynchus mykiss (à la fois évadée et sauvage), dominant la zone littorale et Percichthys trucha natif qui domine les couches moyennes et profondes. Un faible comportement piscivore-benthivore et un régime zooplanctivore important ont été observés pour la truite arc-en-ciel, les deux traits étant peu fréquents à l'échelle régionale. Le régime de la truite arc-en-ciel échappée des cages (ERT) comprenait des composés indigestes abondants et des proies sauvages. Un coefficient de condition élevé de P. trucha près des fermes, ainsi que l'incidence locale sans précédent de Daphnia sp. dans les estomacs de toutes les espèces suggère que les rejets de nutriments aquacoles ont eu des impacts importants. Enfin, le bon état corporel des ERT, ainsi que leur régime alimentaire et la longue distance de ...

New Insights into the Distribution, Physiology and Life Histories of South American Galaxiid Fishes, and Potential Threats to This Unique Fauna

“…Damming and the creation of anthropogenic [94], but also natural, reservoirs-e.g., dams created by the Canadian beaver Castor canadensis [95]-have provided new conditions for galaxiid populations [18,96] and also a place for salmonid cage aquaculture. Farmed rainbow trout escapes have been recorded in the Alicura reservoir (Table S1) [88], with consequences for habitat use and food webs [89,90]. Contamination is a new issue for Patagonian waters, and recent results [97][98][99] have sounded an alarm.…”

“…Established salmonid populations resulted in the partial displacement of several native Patagonian galaxiids species from their historical distribution ranges due to negative interactions such as competition and predation [33,87]. Furthermore, escaped farmed rainbow trout in reservoirs have been shown to negatively affect native populations [88][89][90].…”

Thermal effects in rainbow trout (Oncorhynchus mykiss) F1 embryos (farmed female × wild thermal‐resistant male)

“…However, the creation of thermally resistant trout stocks must be carried out with caution, so as not to disturb wild population genetics by bringing about unintentional alterations to genetic lines (Crozier et al, 2019). Fish escapes from trout cages and their undesirable environmental effects are well documented (Cussac et al, 2014;Nabaes Jodar et al, 2017, 2020. Moreover, exotic trout and chars introduced into Northern Patagonia are in decline because of global warming (Aigo et al, 2008(Aigo et al, , 2014, which in terms of nature conservancy is an unexpected positive side effect that should not be disturbed.…”

“…Fish escapes from trout cages and their undesirable environmental effects are well documented (Cussac et al, 2014;Nabaes Jodar et al, 2017, 2020. Moreover, exotic trout and chars introduced into Northern Patagonia are in decline because of global warming (Aigo et al, 2008(Aigo et al, , 2014, which in terms of nature conservancy is an unexpected positive side effect that should not be disturbed.…”

Distinct resource utilization by introduced man-made grouper hybrid: an overlooked anthropogenic impact from a longstanding religious practise

“…Examples from farm escapes of aquaculture species, such as the rainbow trout Oncorhynchus mykiss suggests that hatchery individuals are capable of consuming a large variety of prey in the wild, some even indistinguishable from wild occurring rainbow trout, with diet also depends on season, size and dispersal distance from the originated fish farm that reflect a diet transition from aquaculture to wild (Nabaes Jodar et al, 2020; Rikardsen & Sandring, 2006). O. mykiss farm escapes was also found to have a broader dietary breadth than wild rainbow trout, although the diet included indigestible items as well (Nabaes Jodar et al, 2017). Yet, the diet of TGGG cannot be measured and compared in the same way as O. mykiss farm escapes, as there is no wild TGGG hybrids to allow direct dietary comparison and interpretation of differences of diet.…”