Rodents populations have been growing steadily over the past years in Amsterdam. The city is becoming more and more densely populated, and the stricter bans on using rat poison are not helping. It so happens that we find rats around the Biotoop, and there might be a use for them after all.
In link with our current efforts to find alternate fish food sources, like duckweed or black soldier flies, we gauged the fish reactions to rodents. African catfishes have been known to eat birds from time to time, and studies have found that lesser salmon catfish can eat large quantities of mice (Kelly, 2016).
The perfect occasion to test this addition to our fish diet presented itself last Thursday, when a rat was found in the Biotoop. It was cut into manageable pieces for the fish, and fed to the most hungry ones in tank 4. It took a bit of time for the fish to get used to this new input but eventually everything was consumed.
There were some worries about rat poison being transmitted to the catfish, but close monitoring will determine whether this is a safe feed source. So far, the fish seem to be doing as good as ever, and rodents might present themselves as a good addiitonal source of proteins. If this is defintely the case, the next step will be to design a way to catch rats and mice consistently and in as clean a way as possible.
Erin Kelly, Kenny J. Travouillon, James Keleher, Susan Gibson-Kueh, David L. Morgan (2016),
Mammal predation by an ariid catfish in a dryland river of Western Australia,
In Journal of Arid Environments (Volume 135, 2016, Pages 9-11)