How Much Should I Treat?

How much should I treat with? That is often the first question one asks when a treatment is necessary. Fish diseases require different treatments at different rates. Identifying the fish disease is the first step. There are several North Carolina Department of Agriculture Animal Disease Diagnostic Laboratories across the state to help in identifying the disease problem.

Once the disease is identified, a treatment can be recommended. Applying the correct treatment at the required rate is necessary to remedy the fish disease. But the question still remains...how much should I treat with? This is because most pond owners do not know the size or the average depth of their pond.

Do you know the size of your pond? What is the average depth? There are methods to help to determine the surface acreage of your pond and the average depth.

Rectangular or square ponds can be measured by pacing or a tape measure. The length and width of the pond needs to be measured.

Surface area = length (feet) x width (feet) = area ft²
Area = ft²/43,560 ft² = surface acres

If the pond is circular, the circumference needs to be measured. The circumference is the distance around the shoreline.

Surface area = circumference (feet) x circumference (feet) = area ft²
Area ft²/547,390 = surface acres

Many ponds are irregularly-shaped. Approximate the pond shape as either square, rectangle, or circle by measuring the boundary lines that most nearly represent the actual shoreline. This pond shape can be approximated as a rectangle.



Surface area = length (feet) x width (feet) = area ft²
Area ft²/43,560 ft² = surface acres

If the pond is triangular, the base and the height should be measured. Multiply those two numbers, take half of the resulting amount, and divide by 43,560.

Surface area = width (feet) x height (feet)/2 = area ft²
Area ft²/43,560 ft² = surface acres

Average Depth Calculation

Average depth can be determined by taking uniformly-spaced soundings over the entire pond surface. This can be done from a boat. The measurements can be taken with a long pole, chain, or weighted rope marked off in feet. At least 15 measurements should be taken. Add the measurements and divide the number of measurements taken.

Frequency of Measurements

Pond measurements should be re-taken whenever there is an appreciable change in either surface area or average depth. Significant changes in surface area occur when existing ponds are enlarged. However, average depth changes very gradually over a period of years as a result of natural processes. Sediment inflow and the accumulation of decomposing vegetation will cause a pond to gradually become shallower. A pond that may have been 15 feet deep when it was constructed may only be 10 feet deep after several years. Average depth should be re-calculated every five years to account for gradual filling in of the pond. Soil disturbances in the watershed or excessive accumulation of decomposing vegetation in the pond will require more frequent measurement of the water depth.

Let's Make Some Pond Measurements

I would like to offer my assistance in making your pond measurements. We can have on record how big your pond is. When making treatments, you can start with a better estimate of how much to treat. All you need is a boat or canoe to take us over the pond surface. Please contact me to schedule an appointment.

Bacterial Coldwater Disease

Skip Thompson wrote about Bacterial Coldwater Disease in his last version of Trout Aquaculture Newsletter volume 19 number 1. Here is what he has to say about it...

Bacterial Coldwater Disease (BCWD) is usually seen when water temperature is between 60-70 ^oF. One sign of the disease is the erosion of the tail (caudal) fin. Another sign is a discolored area above and slightly in front of the anal fin that becomes an ulcerated lesion that looks like a 'scooped-out' area.

BCWD usually affects trout less than 6" in size but chronic mortality can be seen in fish larger than 6". As the disease progresses, trout can be seen with the entire caudal fin missing with erosion of the peduncle or fleshy part just in front of the fin. Another name for the disease is peduncle disease.

Prevention & Control

BCWD can apparently enter trout eggs and is not sensitive to a standard treatment of 100 ppm iodophor (Wescodyne, Argentyne, etc). Instead eggs should be disinfected with Hydrogen Peroxide at 100 ppm (4.1 mL/gal of water at 35% active ingredient) (28.7 mL/gal of water at 5% active ingredient).

Routine flow-through treatments at 1.0-1.5 ppm Hyamine^® or other quaternary ammonium compounds reportedly are effective in prevention and in the early stages of infection. However, this approach is not effective once the disease has progressed to erosion of the peduncle and caudal fin.

Stress associated with rearing density contributes to higher level of mortality. In fact, the level of mortality usually will decrease if the trout are simply split into two or more raceways, lowering the density. Mortalities and trout showing the symptoms should be removed quickly since dead trout shed almost 70 times more bacterial than live trout.

If you choose to use an antibiotic, Terramycin^® (oxytetracycline) is not effective when used at the approved rate of 2.5-3.75 g/100 lbs of fish for 10 days. However, Terramycin^® is reportedly effective when used at 16.5 g/100 lbs of trout for 10 days.

Aquaflor^® was approved for use in March 2007 against BCWD at 0.454 g/ 100 lbs of trout for 10 days, and the withdraw period is 15 days. It is worked well in North Carolina. In most instances with BCWD, it is best to first reduce the fish density and then use the antibiotic.

Disease Spotlight: Ich

It is getting close to that time of year when disease problems are more prevalent! Last year for the first time I identified Ichthyophthirius multifiliis (Ich) in a carp pond. Ich has also been referred to as White Spot. Ich is highly contagious and can spread quickly.

White spots on the skin or gills of the fish is a classic sign of Ich. The white spots are like small grains of salt that have been sprinkled over the skin of the fish. Fish may also appear to be irritated and have decreased activity--don't bite.

Ich goes through a life cycle. The breeding stage is when the parasite gets on the host skin. When this stage matures it leaves the fish and produces many, many young. These young must find a fish host in order to survive. This is the free-swimming stage of Ich.

Disease Treatment

Treatment can be difficult because the breeding stage is protected. The free-swimming stage is susceptible to treatment. Since the life cycle is dependent on water temperature so is the application of treatments. A single treatment will not do the job; multiple treatments are needed. The water temperature determines the timing of the treatments. Warmer temperatures (75-79^oF), treatments are performed every other day. Cooler temperatures (60^oF) require treatments to be performed 4 to 5 days apart.

A common treatment is copper sulfate. Beware, copper sulfate can be toxic to fish at low alkalinities. Alkalinity must be measured before treatment. The concentration of copper sulfate is determined based on alkalinity.

Potassium permanganate is another option for those you can not use copper sulfate.

Remember, treat on sunny days. Many treatments kill the oxygen producing plankton in your pond. Have emergency aeration available. Aerators also help to mix the treatments in the pond.

Before treating, the correct diagnosis is essential. Please consult with your local extension agent about disease identification and treatment.

On a less serious note, in a local retail store in the Health & Beauty section, the aisle is labeled "Ich Relief". I chuckle to myself each time I pass it. (It is meant to be "Itch Relief").