Interesting. Thank you for this. This goes against the norm as we know and understand it. So these cases you describe with the RB piranha and the pacu might be exceptions or there could have been something that requires further clarification and thinking.
Groundwater temps in MA are between 48F and 54F. So in winters, even the deepest of ponds and lakes are unlikely to provide quick and efficient enough geothermal heating to keep the water even at 50F.
One exception might include sources of warmer waters, for instance from warm springs (IDK if there are such in MA) or from power stations discharges of water.
People here in Florida are able to keep pacu in ponds with the help of pumping lots of well water into their ponds in cold spells / snaps but our groundwater temps in southern FL are 70-75F. If they don't do it, pacu and other tropical monster fish they keep die.
Our own experiment with pacu was in a shallow (3ft) 30,000 gal pond outdoors where pacu died when the water seasonally cooled to about 60-55F.
Groundwater temps in MA are between 48F and 54F. So in winters, even the deepest of ponds and lakes are unlikely to provide quick and efficient enough geothermal heating to keep the water even at 50F.
One exception might include sources of warmer waters, for instance from warm springs (IDK if there are such in MA) or from power stations discharges of water.
People here in Florida are able to keep pacu in ponds with the help of pumping lots of well water into their ponds in cold spells / snaps but our groundwater temps in southern FL are 70-75F. If they don't do it, pacu and other tropical monster fish they keep die.
Our own experiment with pacu was in a shallow (3ft) 30,000 gal pond outdoors where pacu died when the water seasonally cooled to about 60-55F.
