Backyard Shrimping Equipment: Substrates*

* This document is a portion of the Backyard Shrimping Project. Click the "Home" button to review our effort.

A substrate is a collection of "frames" that have webbing to increase the available surface area for the shrimp. The use of substrates can more than double the surface area of a pool. Research at Kentucky State University's Division of Aquaculture has indicated that the color and orientation of the substrates has no significant impact on the prawns' ability to grow (1), (2). Upstrom at Aquaculture of Texas used substrates that were PVC "boxes" with layers of mesh that were deployed horizontally.
box substrate shrimp tank
We had constructed horizontal frame substrates and then decided to use vertical substrates in our second pool. We have included the process for determining the maximum sized horizontal substrate below. Our vertical substrates are sections of industrial polyethylene netting that is suspended on PVC pipes that are a maximum of 10 feet long.

The Process

Equipment and Tool List

Here is a list of the things you will need to construct your substrates that are used to increase the available surface area for the shrimp. We also have included recent costs and Amazon links to assist your ordering the part. Click on the image to see specifications or to order from Amazon as it will help fund our efforts to provide sustainable urban shrimp farming in your backyard.

Calculate Maximum Substrate Area

We are using round "tanks" that are steel-framed above-ground swimming pools. The vertical substrates are hanging pieces of industrial netting. The horizontal substrates are PVC frames with the substrate material stretched across the frame.

Horizontal Substrates

We needed to determine the largest "square" that would fit in our pool. We are using a 12' diameter steel-framed pool for each of our "tanks". Consider the following illustration:
circle_square
In the figure above, we have drawn an equilateral square, with each corner "touching" the circle. Note that if we draw a line from one corner to the opposite corner to form two triangles, the length of this line (hypotenuse of the triangle) is the same as the diameter of the circle (line C"). "A" and "B" are sides of the original square that are the remaining two sides of one of the triangles. Using the Pythagoen Theorem from Middle school geometry, We can derive the following:
A2 + B2 = C2. C is the diameter of the pool, 12'. A and B are the same length. So:

A=B, substituting into the equation gives us A2 + A2 = (12')2 or 2A2 = 144 ft2. A2 = (144/2), A2 = 72 ft2. So A = √72 = 8.485 ft.

We will use frames that are 7' long to allow some access space from the side of the pool. The PVC pipe we are using comes in 10' lengths. To reduce the amount of waste pipe, we have made the width of each frame 2.5' (4 pieces per 10' pipe).

Each frame needs to be 2" apart to allow the shrimp to swim between the stacked frames that compose our "box". The pool is 36" tall, so we can stack 12 frames on 2.5" centers to allow some space from the top of the pool.

Building the Substrates

Horizontal Substrates

For each "layer in the substrate, we constructed 7' x 2.5' frames using 2 7' PVC lengths, 2 2.5' PVC lengths, and 4 1/2" PVC 90° angle couplings. In order to secure the frame joints, we drilled 1/4" holes through the coupling into the pipe, then inserted plastic bumper attachment pugs into the holes. Each frame is supported by 4 30" sections of 1.5" PVC pipe.

  1. Cut 2 10' lengths of pipe into 7'and 3' pieces.
  2. Put 1 90° coupling on each end of the 7' pipe sections. Secure each coupling onto the pipe by tapping each with a hammer or mallet.
    frame coupling hammering corner
  3. Connect the 7' lengths together with the 3' lengths to form a rectangle (frame).
  4. Drill 2 1/4" holes through the coupling into the pipe, one hole per "arm" of the coupling.
    bumper plugs circle_square
  5. Cut 7.25' length of the netting. Secure the netting with 2 bumper plugs that are evenly placed on each 3' side of the rectangle. Use 3 cable (zip) ties on each of the 7' sides to secure the netting.
    frames
  6. Fabricate the frame supports by cutting 2 30" sections of 1.5" PVC pipe in half lengthwise. Make 2 0.5" cuts into the flat side of each section, 0.5" apart to form "tabs" on 2.5" centers. Using heavy duty angle pliers, bend the pvc to form the tabs. The sides of the frame will be inserted into the "notches" below these "tabs".
    frame supports
  7. Build the "box" by inserting the 7' side of one frame into the support "notch" under the "tab". Space one support approximately 2' from the end of the frame. Drill a 1/4" hole through the middle of the support "notch" into the frame side Use a bumper plug to connect the support to the side of the frame. Do the same for another support that is approximately 2' from the other end of the frame.
  8. Repeat step 7 for the other 7' side of the frame.
  9. Repeat steps 7 and 8 until you have mounted all 12 frames. The substrate "box" is now complete and ready to place in the pool.

References

  1. see Tidwell, et al, 2002, http://onlinelibrary.wiley.com/doi/10.1111/j.1749-7345.2002.tb00479.x/abstract
  2. see Tidwell and Coyle, 2008, http://onlinelibrary.wiley.com/doi/10.1111/j.1749-7345.2008.00162.x/abstract