SRAC Publication No. 463

II

January 1992

SouthernRegionalAquacultureCenter

Ammonia in Fish PondsRobert M

Ammonia is the major end pro-duct in the breakdown of proteinsin fish. Fish digest the protein intheir feed and excrete ammoniathrough their gills and in theirfeces. The amount of ammonia ex-creted by fish varies with theamount of feed put into the pondor culture system increasing asfeeding rates increase. Ammoniaalso enters the pond from bacterialdecomposition of organic mattersuch as uneaten feed or dead algaeand aquatic plants.

Forms and toxicityTotal ammonia nitrogen (TAN) iscomposed of toxic (un-ionized)ammonia (NH3) and nontoxic (ion-ized) ammonia (NH+4). Only afraction of the TAN exists as toxic(un-ionized) ammonia, and a bal-ance exists between it and the non-toxic ionized ammonia:

H ++ ( N H3) (NH+ 4)The proportion of TAN in thetoxic form increases as the tem-perature and pH of the water in-crease. For every pH increase ofone unit, the amount of toxic un-ionized ammonia increases about10 times. The amount of toxic un-ionized ammonia in your pondcan be found by measuring theTAN with a water quality test kitand then looking up the fraction ofTAN that is in the toxic form on

N H4 + NH3 (TAN)

b a c t e r i am ine ra l i za t i on

NO2 n i t r i t euptake bacteria

algae bloom N O3 nitrate

f i x a t i o n

volati l ized

1Cooperative Extension Program, KentuckyState University

2Mississippi Cooperative Extension Service

Durborow1, David M. Crosby and Martin W. Brunson2

Table 1, which is based on watertemperature and pH. Multiply thisfraction by the TAN to find theconcentration (mg/L or ppm) oftoxic un-ionized ammonia presentin the water. For example, if waterpH is 8.6, water temperature is30C, and TAN is 3 mg/L (ppm),multiply 0.2422 (from Table 1) by 3mg/L (ppm) to obtain 0.73 mg/ L(ppm) toxic un-ionized ammonia.Uptake (assimilation) of ammoniaby plankton algae is important inreducing the amount of ammoniacoming in contact with fish. Am-monia increases in the fall andwinter because of reduced algaepopulations in the pond and algaepopulations which are not as capa-ble of taking ammonia from thewater. Additionally, lower watertemperatures slow down aerobicbacterial activity, thus slowing thevitrification proc-ess whereby am-monia is con-verted to harm-less nitrate (Fig-ure 1). Algae die-offs can also leadto very high am-monia concentra-tions, but, fortu-nately, the lowpH associatedwith the disap-pearance of thealgae reduces theproportion oftoxic un-ionizedammonia pre-sent.

Dangerous short-term levels oftoxic un-ionized ammonia whichare capable of killing fish over afew days start at about 0.6 mg/L(ppm). Chronic exposure to toxicun-ionized ammonia levels as lowas 0.06 mg/L (ppm) can cause gilland kidney damage, reduction ingrowth, possible brain malfunc-tioning, and reduction in the oxy-gen-carrying capacity of the fish.

TreatmentsTreatment for high TAN concen-trations is difficult in large pondculture systems. Pumping freshwater into the pond is not a practi-cal or economical means of reduc-ing the ammonia level for thewhole pond. It does, however, pro-vide a small area near the inflow-ing water where fish can go to findsome relief. Maintaining high dis-

feed

uneaten

fish feed

N O2 N i t r a t edentrification

N2 (anaerobic)(gas)

Figure 1. Nitrogen cycle in a fish pond.

solved oxygen levels by aerationwill slightly reduce the toxic effectof un-ionized ammonia. Inaddition, TAN levels may be re-duced through increased aerobicbacterial activity due to higheroxygen levels. Temporary reduc-tion of feeding rates is recom-mended until TAN levels decreaseto an acceptable level.

However, the organic loading inthese systems is a major factor that

Prevention of high TAN is a betterapproach to the problem. The useof lower feeding rates and goodfeeding practices play a big role inkeeping TAN levels low. Problems

with high TAN concentrations canbe expected when feeding rates ex-ceed 100 pounds per acre per day,or when excessive feed waste is oc-curring. Fish should not be over-fed, and the feeder should be surethat fish are consuming feed of-fered. This is both of practical andeconomic importance, since feedcosts are a major portion of pro-duction costs.With pond and tank stocking den-sities continually increasing it isnot often considered economicallypractical to reduce feeding rates.

. ,

must be dealt with. Intensive recir-culating systems may be bettersuited to handle these excessiveamounts of nitrogen, but mostpond systems probably have a fi-nite limit to the amount of nitro-gen and organic loading that canbe managed. Unless more efficientmanagement methods are devel-oped, nitrogen and organic load-ing may become a limiting factorin stocking and production ratesin culture ponds.

Table 1. Fraction of toxic (un-ionized) ammonia in aqueous solutions at different pH values and tempera-tures. Calculated from data in Emerson, et al. (1975).To determine the amount of un-ionized ammonia present, get the fraction of ammonia that is in the un-ionizedform for a specific pH and temperature from the table. Multiply this fraction by the total ammonia nitrogen pre-sent in a sample to get the concentration in ppm (mg/L) of toxic (un-ionized) ammonia.

Temperatures (C)pH 6 8 10 12 14 16 18 20 22 24 26 28 30

7.0 .0013 .0016 .0018 .0022 .0025 .0029 .0034 .0039 .0046 .0052 .0060 .0069 .0080

7.4 .0034 .0040 .0046 ,0054 .0063 .0073 .0085 .0098 .0114 .0131 .0150 .0173 .0198

7.8 .0084 .0099 .0116 .0135 .0157 .0182 .0211 .0244 .0281 .0322 .0370 .0423 .0482

8.6 .0510 .0593 .0688 .0795 .0914 .1048 .1197 .1361 .1541 .1737 .1950 .2178 .2422

9.0 .1190 .1368 .1565 .1782 .2018 .2273 .2546 .2836 .3140 .3456 .3783 .4116 .4453 I

9 . 4 . 2 5 3 3 .2847 .3180 .3526 .3884 .4249 .4618 .4985 .5348 .5702 .6045 .6373 .6685

9.8 .4600 .5000 .5394 .5778 .6147 ,6499 .6831 .7140 .7428 .7692 .7933 .8153 .8351

10.2 .6815 .7152 .7463 .7746 .8003 .8234 .8441 .8625 .8788 .8933 .9060 .9173 .9271Source: Emerson, K., R.C. Russo, R.E. Lund, and R.V, Thurston. 1975. Aqueous ammonia equilibrium calculations: effect of

pH and temperature. Journal of the Fisheries Research Board of Canada. 32:2379-2383.

The work reported in this publication was supported in part by the Southern Regional Aquaculture Center through Grant No. 89-38500-4516 from The United StatesDepartment of Agriculture.