Aquacultural Engineering 24 2000 1 – 14
Nitrogen transformations and balance in channel catfish ponds
Amit Gross
a
, Claude E. Boyd
a,
, C.W. Wood
b
a
Department of Fisheries and Allied Aquacultures, Auburn Uni6ersity, Auburn, AL
36849
-
5419
, USA
b
Department of Agronomy and Soils, Auburn Uni6ersity, Alabama
36849
-
5419
, USA Received 29 March 2000; accepted 24 July 2000
Abstract
A nitrogen N budget was developed for four, 400-m
2
ponds stocked with 550 channel catfish Ictalurus punctatus fingerlings that were fed to satiation daily for 133 days with a
ration containing 4.85 N. Feed accounted for 87.9 of the N input to ponds. Abundant N from ammonia NH
3
, ammonium NH
4 +
, and nitrate NO
3 −
and the high total N: total phosphorus ratio in pond waters prevented appreciable biological N
2
fixation. There were four main N losses: fish harvest 31.5; denitrification 17.4; NH
3
volatilization 12.5; accumulation in bottom soils 22.6. Nitrification averaged 70 mg N m
− 2
d
− 1
, denitrifica- tion averaged 38 mg N m
− 2
d
− 1
, and phytoplankton removed NO
3
N at 24 mg N m
− 2
d
− 1
. Mineralization of feed N to NH
3
averaged 59 mg N m
− 2
d
− 1
. As feed is the largest N input in catfish ponds, improved feeds and feeding practices can increase the proportion
of N recovered in fish and reduce the amount of NH
3
excreted by fish. Efficient aeration and water circulation also should enhance nitrification and oxidation of organic N. © 2000
Elsevier Science B.V. All rights reserved.
Keywords
:
Channel catfish; Pond aquaculture; Nitrogen cycling; Water quality www.elsevier.nllocateaqua-online
1. Introduction
Nitrogen N is important in pond aquaculture because it is a major component of plants and animals and influences productivity. There have been many studies of
N dynamics in aquaculture ponds Hargreaves, 1998. Some of these studies
Corresponding author. Tel.: + 1-334-8444786; fax: + 1-334-8445933. E-mail address
:
ceboydacesag.auburn.edu C.E. Boyd. 0144-860900 - see front matter © 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 1 4 4 - 8 6 0 9 0 0 0 0 0 6 2 - 5
provided partial or complete N budgets. Avnimelech and Lacher 1979 and Schroeder 1987 estimated N inputs and outputs to aquaculture ponds in Israel,
but relatively little information was provided on N dynamics. Boyd 1985, Daniels and Boyd 1989, and Green and Boyd 1995 measured N inputs and
outputs of aquaculture ponds, but N dynamics were given brief consideration. Studies by Krom and Neori 1989, Acosta-Nassar et al. 1994, and Briggs and
Funge-Smith 1994 also provide estimates of N inputs and outputs to ponds. According to Hargreaves 1998, there is still a need for a more complete under-
standing of factors regulating ammonia and nitrite concentrations and exchange of nitrogenous compounds between sediment and water in aquaculture ponds.
The N balance and N dynamics are of interest in channel catfish Ictalurus punctatus culture. Channel catfish farming is a large industry in the southeastern
United States with a production of about 268 000 tons in 77 000 ha of ponds in 1999 Anonymous, 2000. Channel catfish are fed a commercial ration and the
feed conversion ratio is about 2. Annual production averages 3500 kg ha
− 1
, so feed use is about 7000 kg ha
− 1
yr
− 1
. Catfish feeds contain 25 – 36 crude protein or 4 – 5.8 organic N ON Lov-
ell, 1989. About 25 – 30 of N in feed is recovered in fish at harvest, and the rest enters the pond ecosystem Boyd and Tucker, 1995, 1998. Fertilizers are
seldom applied to channel catfish ponds. Nitrogen fixation has not been mea- sured in channel catfish ponds but is not considered important as a N source
Boyd and Tucker, 1998. Thus, feed is the major N input. Fish excrete NH
3
through their gills, and bacteria mineralize ON in uneaten feed and feces to NH
3
. Ammonia reacts with water to produce ammonium NH
4 +
and hydroxyl ions, and therefore an equilibrium exists between NH
3
and NH
4 +
. The sum of NH
3
and NH
4 +
is total ammonia N TAN. Large additions of feed cause high con- centrations of TAN in pond water, and NH
3
may reach concentrations harmful to fish. High TAN concentrations in effluents can pollute natural water bodies
Schwartz and Boyd, 1994. The amount of N in pond ecosystems, and poten- tially in effluents, is less than the difference between feed N and fish N. This
results because NH
3
is volatilized from pond surfaces Bouldin et al., 1974; Gross et al., 1999a and oxidized to nitrate NO
3 −
by nitrifying bacteria. Nitrate is used as an electron acceptor by denitrifying bacteria and transformed to N gases
N
2
and N
2
O that diffuse into the atmosphere Boyd and Tucker, 1998. Nitro- gen is stored in pond sediment as ON and NH
4 +
, and N compounds are con- tained in waters that seep from ponds. Although the processes involved in N
dynamics of ponds are well known, the relative importance of the different fluxes have not been elucidated clearly.
The purpose of this study was to obtain more information on N transforma- tions and N balance in channel catfish ponds. A better understanding of these
two topics will be useful in maintaining better water quality in ponds. Also, the information may be helpful in improving management techniques to lower the
concentrations of nitrogenous compounds in pond effluents.
2. Materials and methods
