Northeast North Carolina Aquaculture Newsletter

HACCP for Producers Meeting Scheduled

A Hazard Analysis Critical Control Point (HACCP) for Producers meeting has been scheduled for Tuesday, September 21, 1999 from 10:00 am until 3:00 pm at the Vernon James Research/Extension Center in Plymouth. This HACCP meeting is designed specifically for fish producers and will cover exactly what HACCP means for the aquaculture producer by identifying those producers who need to be very concerned about the regulations, those who need to be mildly concerned and those who don't need to be concerned at all.

In December, 1995, the U.S. Food and Drug Administration published the final regulations as part of the Federal Safe Seafoods regulations, of which HACCP is a part. The regulations went into effect in December, 1997. Although the regulations specifically target seafood processors, to varying degrees, it also affects fish producers. All fish farms should have a hazard analysis, which is part of the HACCP program, but most farms may not be required to have the full fledged HACCP plan in place. The purpose of the meeting is to explain what HACCP is and identify who is covered under the varying levels of the regulations.

The meeting will begin at 10:00 am with discussions and presentations. There will be a lunch break from noon to 1:00 pm when the meeting will be reconvened with a walk through example of a typical hazard analysis for the typical fish farm. State and Federal regulatory officials will be present to answer any specific regulatory questions. The meeting will adjourn by 3:00 pm. Those attending will receive a certificate from the N.C. Cooperative Extension documenting their attendance at this educational meeting.

Using Diuron in Fish Ponds

In April, 1999, the Environmental Protection Agency gave the Mississippi catfish producers temporary approval (official approval ends December 31, 1999) to use the broad spectrum herbicide, Diuron, in catfish ponds, as an algicide to control blue-green algae blooms and specifically, the blue-green algae associated with off-flavor. Diuron is effective at killing algae, especially the species of blue-green algae responsible for the most common off-flavor problems in Mississippi, at very low concentration levels. Also, at these low concentration levels, it is relatively safe for the fish and humans. An added bonus is that Diuron's toxicity is not affected by water quality parameters like copper sulfate's, making it easier to establish consistently effective application rates. Several other states have also received permission to use this herbicide on the same emergency basis. However, North Carolina DOES NOT have clearance to use Diuron in food fish ponds since North Carolina does not have an off-flavor problem. The use of Diuron in food fish ponds in North Carolina would be in violation of state and federal law and could jeopardize the potential legalization of the chemical for the whole U.S. aquaculture industry.

Drain Pipe Discharges

In order to use the chart accurately, you must understand the information on the chart. The chart is based on drain pipe made of 60 feet of PVC pipe with 2 couplings and 1 ninety degree ell. The numbers listed for each depth of stand pipe for the different sizes of drain pipe corresponds to the gallons per minute that is draining through the pipe at that depth and the minutes it will take to drain 1 acre of water at that flow rate. For example, using an 8 inch drain pipe, at 5 feet (when the drain pipe is 5 feet below the surface of the pond) 1396 gallons per minute are flowing through that pipe and at that rate it would take 117 minutes to drain 6 inches per acre of water from the pond. However, as the water level drops, there is less water over the pipe forcing the water through the pipe (elevation head) so the flow decreases. This means that as the water level drops, the flow rates decrease, causing drain times to increase. Fortunately, as you can see in the Drain Pipe Discharges graphs, this decrease in flow rates and increase in drain times are pretty much linear (straight line) until you get to a depth of about 1 foot. This means that you can average the flow rate and minutes of drain time at the 5 feet of depth and at the 4 feet of depth to come up with the average discharge rate and the amount of time it would take to drain that foot of water. This number is the 4.5 foot reading and for an 8 inch drain pipe would be 1323 gpm and about 123 minutes.

When you start working with depths of less than 1 foot, things become more complicated. This is because there is less water (elevation head) over the drain pipe to "push" the water through and you are often times "sucking air" when the pipe is not full. Therefore, water flows at slower and slower rates and are more exponential than linear. To account for this, the chart is broken down into smaller increments (3 inch and 1 inch) than the 6 inch ones.

Using the chart is relatively easy. If you have a swivel stand pipe located inside the pond. Measure the diameter of the pipe. Once you decide how much water you want to drain, that will be the distance the top of the stand pipe will be to the surface of the water. Take that distance to the chart and under the correct pipe size add the minutes under the drain time, beginning with full pond distance (depth from the surface to the pipe outlet) and ending with the depth the stand pipe will be when stopping the draining process. The total will be an approximation of time it will take to drain that amount of water per acre of pond. For example, if you have a 10 acre pond that you want to drain the top 6 inches of water from 5 feet to 4.5 feet with a swivel drain pipe that was 10 inches in diameter, you would add 231+163+100=494. It would take at least 494 minutes per acre or at least 4940 minutes (about 3.5 days) to drain the top 6 inches of water from the 10 acre pond. The drain time is actually longer than that since the calculations are based on a full pipe flow and toward the end of the draining process, the pipe would not be full.

An outside swivel pipe would work the same way. However, if you had a drain pipe with a stand pipe on the outside that did not swivel and a valve on the drain pipe, the calculations would be different. First, the top of the drain pipe would then be 5 feet below the surface of the water. Because of this, it would take at least 72 minutes to drain the 6 inches of water from the 5 foot level to the 4.5 foot level. This difference between this drain time and the previous example is due to the 4.5 to 5 feet of elevation head pressure which is forcing water through the pipe at that greater flow rate. Also, the addition of a valve to the initial assumptions for the drain calculations will decrease the flow rate and increase the drain time to some extent.

This chart should also be able to assist you in anticipating draining rates in the event of heavy rainfall. By knowing what your drain pipe capabilities are, you should be able to make adjustments for predicted rainfall amounts, both before and during such an event.

As a reminder, any variation from the assumptions of 60 feet of PVC pipe, 2 couplings, and a 90 degree ell will alter the calculations to some extent. If you would like your pond drain times calculated to your specifications so you will have a more approximate drain rate and time, give me a call. A list of fittings, pipe material, pipe size, pipe length, and elevations will be necessary for the formulas.

Some other numbers that could be helpful are: