Prawn Project Update

When Hubby and I started our little prawn experiment back in June, we had high hopes of sitting down to a prawnfest of giant freshwater prawns in October, plus a freezer full to last us till next season. In September’s Harvest Update, they still hadn’t grown that much. The tank with the biggest prawns were killed by me (and my menopausal brain) when I accidentally left the bubbler off. The good news is, the twenty or so that I thought was left in the remaining tank, turned out to be a hundred!

What a difference in size, this is common, especially in a tank environment.
The presence of larger blue-clawed males suppresses the growth of the other males in the tank.

Hubby scooping out the prawns to be moved into the house for winter.

The majority are kept in a large aquarium in the basement which we got for next to nothing on Craigslist. The four biggest, toughest boys are in the smaller tank upstairs in our dining room. By removing the larger prawns, it gives the smaller males a chance to grow faster. They are fascinating, I could sit for hours watching them posture for better tank position, groom and feed themselves, and molt. Aquariums have always intimated me because it seems so complicated with filters and constant water testing, but it was necessary for these guys to continue their grow out through winter.

Everything seemed fine for the first few days, then they started dying. Everyday, another handful of prawns were scooped out of the large tank. The water turned from clear to murky white. After some Googling, it was apparent that we were suffering from New Tank Syndrome, where both tanks became the breeding ground of a bacterial bloom. We made the mistake of not “cycling” the tank before we added livestock.

White murkey water indicates the presence of bacteria in the water.

These prawns were dying from ammonia and nitrite levels rapidly rising in the water due to the organic waste from their poop and feed. The cycling period would have allowed beneficial bacteria to build up and take care of this, breaking down toxic ammonia and nitrites, and turning it into nitrates. Which is exactly what the aquaponics system was doing in the greenhouse. Clay pebbles (loaded with beneficial bacteria) from the greehouse aquaponics bed were added to both aquariums. Hopefully they will multiply in time to balance things out before we lose the entire crop.

Plastic bird netting was added to increase their surface living area and provide a safe place to molt.

Amazing how they can snap at the neck and wriggle out of their shell.

New molts are pale and translucent, vulnerable until the new shell hardens in a couple of days.

The biggest one-clawed male got his second claw back after his molt. Imagine losing an arm and then growing it back.

Crop, weird to refer to these little prawns as crop. After watching them go through molts, and protecting them from cannabilizing each other, I’m not sure if I will be able to “chill kill” and eat them when the time comes. If all goes well, we will be able to breed them in February.