Rainbow trout culture in the context of climate change

The Alicura dam –located between the provinces of Neuquén and Río Negro– is the main site for breeding rainbow trouts in Argentina. However, the sustainability of this practice is under risk as climate change led to a steady increase of temperature of their waters in the last years.

In order to solve a problem that could increase with time, a group of CONICET researchers study the possibility of producing a line of rainbow trouts capable of achieving better results under warmer temperatures. The results obtained so far were published in Aquaculture Reports.

“According to our data, the increase of summer temperatures in the water of the dam –which reaches a seasonal average of 20 degrees Celsius– would be directly linked to a reduction in the last years of the production of rainbow trouts, whose optimum average environmental temperature is close to 15 degrees. The warming of the water negatively affects the development of fish gonads, what limits the reproduction and growth possibilities”, Sonia Crichigno explains. She is a CONICET assistant researcher at the Instituto Andino Patagónico de Tecnologías Biológicas y Geoambientales (IPATEC; CONICET –UNCOMA) and the first author of the study.

The researchers first took juvenile specimens from a rainbow trout population that had been feral for 70 years in the thermal waters of Valcheta stream (Río Negro) –which were already adapted to higher temperature waters– and cultivated them in the Centro de Salmonicultura Bariloche (CENSALBA), an independent experimental breeding under the scope of the Universidad Nacional de Comahue (UNCOMA) located at the Alicura dam. However, that search was not successful.

“We obtained poor growth due to the lack of domesticity of the fish at the moment of ingesting the food we fed them with. Those trouts came from several generations in which the food was captured in motion but in the breedings, the balanced feed is inert. The producers need the fish to fatten in order to sell them. So, if they are not well fed, they are useless for the breeding even whey they can better tolerate high temperatures”, Crichigno explains.

The second option was to try to improve genetically the lots of trouts by crossing specimens raised at the CENSALBA with other feral ones from the warm waters of the Arroyo Valcheta. After that, the scientists undertook a series of experiments to determine how the offspring that came from those crossings adapted to high temperatures.

“We acclimatized the juvenile lots to 20 degrees. Those specimens came from the CENSALBA, in Valcheta, from Boca del Río (Córdoba) and the cross between the CENSALBA and Valcheta (called F1), to assess their degree of adaptation through a series of experiments”, the researcher affirms.

One experiment consisted in verifying the preferred temperature of each of the lots after their acclimation to 20 degrees. The preferred average temperature of the specimens of F1 lot was intermediate to the chosen by those who belong to the CENSALBA and Valcheta, which was even closer than the temperature of those last ones. While the preferred average temperature of the trouts from Valcheta was 21.1 °C and the one of the CENSALBA was 15,6 °C, the F1 lot had 19, 7 °C. The trouts of the Boca del Río breeding chose an average temperature of 16,6 °C.

The researchers also tested the fish of the different lots to measure their thermal tolerance level (linked to the maximum temperature they are capable of resisting without toppling). Again, the tolerance of the F1 lot was intermediate considering the figures obtained by the groups of Valcheta and CENSALBA.

“The trouts of the F1 lot apart from having a better reaction to experiments related to preferred temperatures and tolerance showed a better growth than the other three in terms of size and weight. The Valcheta trouts did not grow due to their problems to take their food”, Crichigno comments.

Although the results obtained are part of an exploratory stage, they are promising as regards the possibility of producing a line of rainbow trout with better performance in high temperatures and capable of keeping their culture in the increasingly hot waters of Alicura dam.

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