SRAC Publication No. 462

June 1997 VI PR Revised

Nitrite in Fish Ponds

Robert M. Durborow1, David M. Crosby2 and Martin W. Brunson3

Nitrite enters a fish culture system Nitrite problems are typically ton activity in ponds (because of after feed is digested by fish and more likely in closed, intensive lower temperatures, nutrient the excess nitrogen is converted culture systems due to insuffi- depletion, cloudy weather, herbi- into ammonia, which is then cient, inefficient, or malfunction- cide treatments, etc.) can result in excreted as waste into the water. ing filtration systems. High nitrite less ammonia assimilated by the Total ammonia nitrogen (TAN; concentrations in ponds occur algae, thus increasing the load on + NH3 and NH4 ) is then converted more frequently in the fall and the nitrifying bacteria (Figure 1). If to nitrite (NO2) which, under nor- spring when temperatures are nitrite levels exceed that which mal conditions, is quickly convert- fluctuating, resulting in the break- resident bacteria can rapidly con- ed to non-toxic nitrate (NO3) by down of the nitrogen cycle due to vert to nitrate, a buildup of nitrite naturally occurring bacteria decreased plankton and/or bacte- occurs, and brown blood disease (Figure 1). Uneaten (wasted) feed rial activity. A reduction in plank- is a risk. Although nitrite is sel- and other organic material also break down into ammonia, nitrite, and nitrate in a similar manner. Brown blood disease occurs in fish when water contains high nitrite concentrations. Nitrite enters the bloodstream through the gills and turns the blood to a chocolate-brown color. Hemoglo- bin, which transports oxygen in the blood, combines with nitrite to form methemoglobin, which is incapable of oxygen transport. Brown blood cannot carry suffi- cient amounts of oxygen, and affected fish can suffocate despite adequate oxygen concentration in the water. This accounts for the gasping behavior often observed in fish with brown blood disease, even when oxygen levels are rela- tively high.

1Cooperative Extension Program, Kentucky State University 2Virginia State University 3Mississippi Cooperative Extension Service Figure 1. Nitrogen cycle in a fish pond. dom a problem in systems with Maintaining at least a 10 to 1 ratio Formula 2 high water exchange rates or of chloride to nitrite in a pond Surface acres x average depth in feet good filtration, systems should be effectively prevents nitrite from x ppm of chloride to add to the pond x monitored year-round, and man- entering catfish. Where catfish (or 4.5 = pounds of salt (NaCl) needed to aged when necessary, to prevent other fish) have bacterial and/or add to the pond severe economic loss from brown parasite diseases, their sensitivity blood in any fish culture facility. to nitrite may be greater, and a You need 4.5 pounds of salt to higher chloride-to-nitrite ratio increase the chloride concentra- Susceptibility of fish may be needed to afford added tion by 1 ppm in an acre-foot of water. species to nitrite toxicity protection from nitrite invasion into the bloodstream. As a general Example Largemouth and smallmouth rule, catfish producers strive to The following readings are bass, as well as bluegill and green maintain at least 100 ppm chloride obtained from a 20-acre catfish sunfish, are resistant to high in pond waters as “insurance” pond with an average depth of 4 nitrite concentrations. The against high spikes of nitrite con- feet: Centrarchids apparently are able centration. Culturists of other to effectively prevent nitrite from species may want to assume that 4 ppm nitrite entering the gills, but most other nitrite is a potential problem and 15 ppm chloride warmwater fishes grown in the use salt as an insurance buffer as Use Formula 1: Southeast apparently concentrate well. nitrite in the blood. Catfish and (10 x 4 ppm nitrite) - 15 ppm chlo- tilapia, for example, are fairly sen- How to calculate the ride in the pond = 40 - 15 = 25 ppm chloride to add to the pond sitive to nitrite, and trout and amount of salt needed other coolwater fish are sensitive Now use Formula 2: to extremely small amounts of Before treatment rates can be cal- 20 acres x 4 feet average depth x 25 nitrite. Goldfish and fathead min- culated, chloride and nitrite con- ppm chloride to add to the pond x 4.5 nows fall in between catfish and centrations in the water, as well as = 9,000 pounds of salt needed to add bass in their susceptibility to pond or tank volume, must be to the pond brown blood disease resulting determined. Commercially avail- from high nitrite levels. Striped able water quality test kits can be Application of salt bass and its hybrids appear sensi- used. Contact your Extension fish- tive to nitrite, but little is known eries or aquaculture specialist for Distribute the salt evenly and about the relative sensitivity com- assistance in locating sources for quickly when fish are suffering pared to other species. test kits and conducting and inter- from brown blood disease. preting these tests. Farmers have used feed trucks, Treatment and prevention The amount of salt needed for the airplanes, paddle wheels, and front-end loaders to distribute Since this is a nitrogen-related pond can be calculated using the following formulas: salt. It takes about 24 hours after problem, the most obvious pre- salt is applied to a pond for the ventive measure is to reduce or Formula 1 brown blood condition to be alle- minimize the amount of nitrogen (10 x pond nitrite concentration) - viated. incorporated into the system by (pond chloride concentration) = parts reducing feeding rates. However, A good water quality monitoring per million (ppm) of chloride to add program can help prevent brown in modern intensive pond or to the pond closed system fish culture with blood disease. Pond water should high densities and rapid growout, The number “10” used in this for- be checked for nitrite two to three longterm feed reduction is not mula is the minimum desired times a week during fall and considered by most farmers as a chloride:nitrite ratio number. It is spring, and at least weekly the viable option. Luckily, although used here to get a 10 to 1 chloride remainder of the year. We recom- we often cannot prevent the to nitrite ratio. If a higher ratio is mend maintaining a chloride-to- occurrence of high nitrite, its desired, substitute the higher nitrite ratio of at least 10:1 for cat- effects can be minimized or neu- number for the 10. fish. Check ponds daily during a tralized safely and economically. If the answer is zero or a negative known high nitrite incident, even number, chloride concentration is if adequate chlorides are in the Sodium chloride (common salt, ponds. Also check chloride after NaCl) is used to “treat” brown sufficient to prevent brown blood disease. periods of heavy rain or active blood disease. Calcium chloride flushing from well water; both can also be used but is typically Use the answer from Formula 1 these events can dilute chloride more expensive. The chloride por- above in the following formula: concentrations and reduce the tion of salt competes with nitrite chloride:nitrite ratio. for absorption through the gills. Nitrite can increase very sudden- days, and nitrite problems can ceptible to bacterial infections, ly, so it is advisable to keep a 100 thus be predicted and then pre- anemia (white-lip or no-blood), ppm chloride concentration at all vented. and other stress-related diseases. times to act as a buffer when In many areas, water contains Secondary problems, such as nitrite suddenly increases. This is high natural concentrations of Aeromonas and Columnaris bac- a standard practice in the catfish chloride, and addition of salt as terial infections, often occur 1 to 3 industry, and incidents of brown “insurance” is not needed. Water weeks after brown blood disease blood disease in catfish ponds should still be monitored fre- occurs. have become very rare. As an quently, however, since chloride Research is currently underway to example, if your water has a chlo- levels can fluctuate widely and determine whether even higher ride concentration of 20 ppm and frequently. levels of chloride may be benefi- you want to increase it to 100 cial in reducing sub-lethal, chronic ppm, simply add 80 ppm chloride Outlook stress on fish from nitrite or other to your pond. Use Formula 2 to stressing factors. Results have calculate the pounds of salt need- Brown blood disease can be pre- thus far indicated significant ed. vented, or at least minimized, by advantages to maintaining chlo- Another way to help manage close monitoring of nitrite, chlo- ride levels as high as practically brown blood disease is by check- ride, and TAN, and by maintain- possible. ing total ammonia nitrogen (TAN) ing the proper chloride-to-nitrite concentrations in ponds every ratio. If brown blood disease does week. Every 1 ppm TAN can con- occur, the condition can be vert to 3 ppm nitrite in a relatively reversed by adding salt to the short period. High TAN levels can water. Catfish (and likely other alert the farmer to anticipate fish) surviving brown blood dis- nitrite problems within a few ease or nitrite stress are more sus- The work reported in this publication was supported in part by the Southern Regional Aquaculture Center through Grant No. 94-38500-0045 from the United States Department of Agriculture, Cooperative States Research, Education and Extension Service.