Dissolved Oxygen (DO), or more appropriately, low DO causes more problems than any other water quality parameter. This is because DO is involved in one of the most dynamic reactions in the fish pond, the photosynthesis and respiration of the algae. The feed and fish wastes supply the nutrients and the sun supplies the energy for the algae to photosynthesize during the day and produce the oxygen while using carbon dioxide (CO2). That is why on a sunny day, as the day progresses, DO levels go up and the CO2 levels go down, causing the pH of the water to go up. At night, respiration takes place, which is the reverse reaction. The algae now needs all the oxygen that it produced during the day and releases CO2, which causes the pH to go down.
The problems with this cycle occurs when there is so much algae producing so much oxygen that the water become supersaturated and loses some of the oxygen off into the atmosphere. At night during respiration, that algae still needs all of the oxygen that it produced, but some of it is gone. The pond then ends up with a deficit of oxygen. If this deficit is not met with aeration, there is a good chance there will be dead fish in the pond by sunrise.
Another way oxygen deficiencies can occur in a pond is when there is a very heavy algal bloom and not very much circulation in the pond. The sunlight penetrates into only a few inches of the surface water, and the rest of the algae is shaded out. The algae receiving the sunlight are photosynthesizing and producing oxygen, while the algae not receiving any sunlight are respiring and using oxygen. After the sun goes down, all of the algae begin to respire, but there is not enough oxygen to go around and again an oxygen deficit can occur. Several consecutive days of cloudy weather can cause the same effect. Not enough algae receives enough light intensity to be able to produce enough oxygen to get the fish through the night.
Fortunately, in nearly all instances, if a person were checking the pond as they should be, these situations could be observed happening, and the necessary precautions could be taken. By checking the DO levels in a pond in the late afternoon, when the DO levels should be at the highest, and then again several hours after the sun has set, and the algae has started to respire, you can estimate the rate at which the algae is using oxygen and estimate when the pond DO levels might become critical. Ideally, DO levels greater than 5 ppm, or above 60% saturation should be maintained for optimum feed conversion and growth. Prolonged exposure to DO levels of 1-5 ppm can cause reduced growth rates.
Total Ammonia Nitrogen (TAN) can also cause problems in a fish pond. The major source of TAN in a commercial fish pond is from the excreted of wastes of the fish. In general, the more feed you put into a pond, the more fish wastes will be generated. The nutrient sink for TAN in a pond is the algae and the bacteria. If for some reason, more TAN is generated in the pond than the nutrient sink can handle, TAN will build up in the pond. There are two forms of TAN, one is toxic (NH3 - un-ionized) and the other one non-toxic (NH4 - ionized). Both forms are found in the water at the same time in a balancing act. The higher the pH and the warmer the water, the greater the percentage of TAN being in the toxic NH3 form. The lower the pH and the cooler the water, the greater the percentage of TAN being in the non-toxic NH4 form. In general, when the pH is below 8.0 and water temperatures are less than 30oC, less than 7.5% of the TAN will be in the toxic form. However, when pH's reach 9.0 with water temperatures of 30oC, almost 45% of the TAN will be in the toxic form. NH3 levels as low as 0.05 ppm can affect growth rates and at levels above 1.5 ppm can kill fish. The most effective way to deal with high NH3 levels is to reduce or even stop feeding of the fish in the pond, thus cut off a significant source of TAN. As the TAN levels drop, feeding can then be resumed.
One of the sinks of TAN in a pond is bacteria. There are two species of bacteria that help break TAN down into a non-toxic form. One species breaks the TAN down into nitrites (NO2) which is toxic to fish. The other bacteria breaks the nitrites down to the non-toxic nitrates (NO3). High nitrite levels in a pond can cause methemoglobinemia (also known as brown blood disease) which limits the amount of oxygen the blood can carry. The best cure for high nitrite levels is a chloride (Cl-) level of 10 ppm for every 1 ppm of nitrites. In general, maintaining a chloride level of 100 ppm (the equivalent of a NaCl - salinity level of 166 ppm) or more in a pond will protect the fish from nitrite toxicities.
Holding crawfish in North Carolina is typically done by holding the crawfish in either a spray system or in cages in the pond. A spray system consists of a method where the crawfish can be enclosed in a cool area out of the sun where they cannot escape, but that drains easily. Water is then sprayed over the crawfish and allowed to drain off. An advantage to the spray system is that the crawfish can be kept cool and their gills moist allowing them to breathe air. When kept under water, dissolved oxygen levels must be monitored.
As the end of June approaches, it is time to think about draining the crawfish pond. Typically, you want to drain the pond at a rate of about 1 inch per day to give the crawfish a chance to burrow down to the water table. This is where the crawfish will spend their summer - in the cool, damp burrow. As the water begins to drop in the pond, the crawfish will begin to burrow in the high ground. This will initially be the newly exposed levee areas around the pond. As the pond becomes nearly completely drained, these areas will be high mounds on the pond bottom and the sides of drainage ditches within the pond. To encourage burrowing, cover can be supplied to these areas in the form of pieces of cardboard and loose straw. This will protect the crawfish from the hot sun and predators. If the pond that is being drained happens to have an overpopulation of crawfish, a way to reduce the population is not to protect it and to drain the pond quickly to strand as many crawfish as possible. Enough crawfish from an overpopulated pond should still survive to serve as brood stock for the next year.
a) sales of commercially manufactured facilities to be used for commercial purposes for housing, raising, or feeding animals or for housing equipment necessary for these commercial activities.
b) building materials, supplies, fixtures, and equipment that become a part of and are used in the construction, repair, or improvement of an enclosure or a structure specifically designed, constructed and used for housing, raising or feeding animals or for housing equipment necessary for one of these commercial activities; and
c) commercially manufactured equipment, and parts and accessories for the equipment, used in a facility that is exempt from tax under this subdivision or in an enclosure or a structure whose building materials are exempt from tax under this subdivision.
A copy of the instructions which outlines G.S. 105-164.13(4C) and form E-599S can be obtain through my office.
The FDA HACCP regulations basically state that any seafood processor must have and implement a HACCP Plan in order to process seafood to insure the seafood safety. So, what is a seafood processor? It is anybody that is engaged in commercial, custom, or institutional processing of fish or fishery products. So what exactly is processing? It is, with respect to fish, the handling, storing, preparing, heading, eviscerating, shucking, freezing, changing into a different market form, manufacturing, preserving, packing, labeling,dockside unloading, or holding of the fish.
There are a couple of exemptions. You do not have to have a HACCP Plan if you:
1) harvest of transport fish or fishery products, without otherwise engaging in processing.
2) are heading, eviscerating, or freezing intended soley to prepare a fish for holding on board a harvest vessel.
3) are operating a retail establishment.
The question has come up, is an aquaculture producer a processor under the Seafood HACCP Regualtions? The answer from FDA is as follows: "No, aquaculture producers are exempt from coverage. Treatment with carbon dioxide, bleeding, washing, and icing of otherwise unprocessed fish by the aquaculture producer is an integral part of the process of harvesting and getting the fish to market, and is, therefore, not considered to be processing. However, heading, gutting, or packaging of fish (e.g. retail or wholesale packages or cartons) performed by the aquaculture producer is considered processing, and would subject the producer to coverage under the regulations".