Submarine Tour of A Shrimp Farm Aboard The USS GoPro

This is your Captain speaking.
Welcome aboard the USS GoPro.
Today we'll be cruising at a maximum depth of approximately one meter as we tour FC's recirculating aquaculture system (RAS).
Secure all hatches.
Prepare to dive.
DIVE!

Don't be alarmed at the giant freshwater prawns (Macrobrachium rosenbergii) peering into your porthole.
Though they are aggressive predators, you are safe inside the USS GoPro.

Here we are cruising at mid-depth to get a look at prawns using the artificial reef.
These panels of plastic mesh give the prawns more habitat within the shrimp farm.
This allows them to spread out and not crowd together.
Crowding equals cannibalism with giant prawns.

If this were a night dive, we would see the mesh panels covered with hundreds of prawns.

Cruising along the tank wall allows us to see how the young giant prawns use the this substrate also.
The sides sport a healthy growth of algae which the prawns constantly prune.

These prawns were born in the spring of 2012.
They were all uniformly sized, about 2 cm long when they arrived as postlarvae back in early May.
There is quite a wide range in growth rates, but the average is probably about 7 cm.
The biggest are around 10 cm.

Thank you for diving aboard the USS GoPro today.

Below is the video ship's log.

Whole Lotta Moltin' Goin' On

The giant Malaysian prawn did it first.
Last week the kids walked in to an "empty" shrimp directly beside the "full' shrimp you see above.

"Wow! He shed!"
" He molted." (not me, another kid)
"Same thing."

"EEuuuuuu! He's eating it!"

Next, the mangrove seeds started. This is the seed of the black mangrove. They sprout on the tree, the better to get growing as soon as they drop to the mud, before an ebbing tide carries them beyond land.

And then, today, Zick (who was being very secretive) began showing signs that she too is in a moltin' mood.

Her eyes have clouded over with the thin film of condensation that occurs when her skin begins to loosen.
Essentially, her windows have fogged up.
That means it won't be long before she molts into her new duds.

I predict tonight is the night.

She was peeking out of her cave and taking a long drink a few minutes ago.
I believe she was contemplating a little swim after I turn the lights out and go home.

A girl needs moisture to soften her skin.

It comes off so much easier that way.

The Last Macrobrachium

 Regular Pure Floridians may remember my Macrobrachium rosenbergii aquaculture project with my kids at my old school.
The students and I built a simple small scale recirculating aquaculture system and grew giant prawns from tiny post-larvae tots to hulking examples of prawnliness.

The system worked great, the shrimp grew well, and losses were minimal.
The only heavy losses were totally due to misjudgement on my part ... underestimating raccoon cleverness and procrastination.
Both of those errors in judgement (again, mine, not the kids) happened in the "in between" time known as summer.
The prawns all came home to spend the summer with me when school shut down. They moved in to my old tilapia tank to spend the summer and await the next school year.

While raccoon predation was not an issue in the classroom, it was a challenge in an outdoor setting.
I covered the tank with old fencing and stopped that issue, but not before losing some prawns to the bandits.

The worst loss of prawns was simply due to waiting one week too long to move them back to class a year ago. A cold snap SNAPPED the last weekend before I planned to transport them back to school.
It was a sad, massive kill.

A few weeks ago, I went out to check on the final survivor (after a cold snap... arrrrgh) and he was on his side, at the bottom, immobile.

Dang!
I did it again.

I dipped him up and ... he twitched!

A quick plunge into an aquarium with fresh 72 degree well water and he revived just fine, thank you maam.

Call me "Lucky".

So Lucky is now living in my new classroom, amazing everyone who sees him and triggering interest in doing the whole thing over again here at Cedar Key School.

What?

Oh ... Lucky says to tell you he's molted since these photos were taken and has a new unbroken rostrum and bright blue claws.

Pride in appearance.

It's a shrimp thang.

Prawn Disaster

I waited one week too long to move the remaining prawns back to the warmth of the tank inside my classroom lab.
Friday night was a cold one, as was Saturday night, and I dropped the ball.

What I should have done is flushed the tank with our 72 degree well water on those cold nights.
Ironically, today was the day I planned to carry them in to school.

There were ALOT more shrimp in here before "Mayhem" the coon struck repeatedly.
I got tired of trapping and transporting him ... what's that saying about the definition of insanity?
Yeah, that one.

So I rigged some hog panel fencing over the top to keep him from fishing the shrimp off the submerged mesh that they liked to climb upon at night.
That was working pretty well.

They weren't all this big of course, but here's what an ALPHA male Macrobrachium rosenbergii looks like.

That big one was 15 inches from telson to the tip his of chelipeds.


The water was cold and the shrimp looked fresh, so it was a tempting thought to eat them ... only, I didn't know for sure when they croaked.

I stifled that idea, but I did preserve about eight of the biggest males in a jar of alcohol so we can use them in class when we study crustaceans.

The others were frozen for bait/fish food.

We (my students and I) are going to order a new batch of postlarvae baby shrimp soon.
I will share that too of course.

This is a cheliped in case you hadn't googled that yet, Miz S.

Giant Prawn Harvest, Part Two

The most humane way to kill these prawns is a slushy ice bath. Being a tropical beasty, the icy water quickly dispatches them.
It also serves the purpose of preventing mushiness in the meat as the prawns contain an enzyme that will quickly break down the muscle tissue if not chilled after death.

I was making blackened tilapia that night, so I cooked the tilapia first and then, after the smoke cleared, the shrimp.

Before cooking the shrimp, I wiped down the cast iron skillet to get rid of any blackening seasoning, as I wanted to taste these shrimp plain on this first taste test.

4 big prawn tails went into a hot skillet with just a smish of EVO, and in a minute or so they were done.


Here's my plate.
Fresh green beans stirfried in a wok with little more than sesame oil, salt, and a spritz of teriyaki sauce, accompanied by some blackened tilapia filet, a sample of this years datil pepper sauce, and two prawns.

They were delicious and so fresh!

I give them an A++.

Giant Prawn Harvest Part One

"From the depths of Hell I strike at thee, human!"

Yesterday, I bit the bullet and harvested a few of my prawns for a taste test.



These guys are pretty fascinating.

They are so cool and with such amazing architecture. Just think of the DNA coding and cellular obedience that must take place for such a multifaceted creature to exist.
It's a bit mind boggling.
But,
... they are predators too and would gladly consume me if I laid still in their tank for long enough, so all's fair ...
Still, after nurturing them from postlarvae, eating them was not a step to be taken lightly.


4 uropods separated by a telson.
Ahhh, ... symmetry.



In the end, I captured about 9 shrimp, 4 bigguns for the taste test (we were having tilapia so 4 was enough) and 5 for a return to the classroom tank.
They are a big hit back in the classroom.
The students have been amazed all day by the giant shrimp patrolling the post summer,empty tank in my room.
Alas, they are only seeing 4 of the intended 5 prawns ... they are quite the predators and only a small piece of #5 was left this morning in the "pen".

Some of the remaining smaller prawns in my RAS should now react to the loss of a bunch of alpha male blue claws by becoming that very thing themselves.


Bear was just a little curious about the live prawns when I took them inside.
This curiosity soon changed to crazed barking and leaping about, so his "nose to rostrum" time with a prawn was cut short.

Tomorrow ... a short prawny video, cooked prawns, and the final exam.

Freshwater Prawn Drawdown

Almost too beautiful to eat.


A look under the kilt.

Dorsal view.

If you are not the lead shrimp, the view never changes.

Of course, if you are a shrimp, it's good to not be on point.

The RAS (test: remember what that stood for?) needed a flushing last week so I popped the knife valve open and drained most of the water out.

This allowed me to get a good look at my livestock and they seem to be growing and thriving.

In a drawdown, I drain the water through a bottom drain and with it goes bottom sediments that build up over time. Once the tank is cleaned, I refill with fresh well water.

The well water comes in at 74 degrees, but the very tropical prawns seem to handle that temperature change (the old tank water would have been warmer due to absorbing the summer heat).

My system rarely needs a drawdown and is very water efficient. On a daily basis, I exchange about 5 gallons of water at the most.

I open the valve for just a moment daily to flush a pulse of uneaten food, etc out of the tank and into the happy plants that grow near the RAS.

A few days after taking these photos, I almost lost the lot of them when a pipe connection came loose.

Most of the aeration in this tank comes from the sprinkling water that returns from the filter barrel. A pump in the tank sends water to the barrel, where it flows through filter media. It returns to the tank (R = recirculating) by spraying back into the tank, thus aerating the water.

I just happened to walk out to feed them a late night snack and discovered the malfunction.

The shrimp were all at the surface (very rare) because that water was the most oxygenated.

The poor things almost suffocated.

I did some late night plumbing repairs (and improvements) and all was well.

Scary business though.

Prawnzilla loves to hide under the substrate fencing and would not come out for a better photo.

He is totally awesome and dominates the tank.

Here's a quiet, not very exciting, yet kind of soothing, video of the prawn parade.

No I haven't eaten any yet, but I think their population will have a sudden drop soon.

I'm thinking broiled like lobster.