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September | October 2013
Understanding ammonia in aquaculture
ponds
The International magazine for the aquaculture feed industry
International Aquafeed is published six times a year by Perendale Publishers Ltd of the United Kingdom.
All data is published in good faith, based on information received, and while every care is taken to prevent inaccuracies,
the publishers accept no liability for any errors or omissions or for the consequences of action taken on the basis of
information published.
©Copyright 2013 Perendale Publishers Ltd.All rights reserved.No part of this publication may be reproduced in any form
or by any means without prior permission of the copyright owner. Printed by Perendale Publishers Ltd. ISSN: 1464-0058
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U
nderstanding	 ammonia	 and	
controlling	it	is	critical	in	aqua-
culture	 systems.	 If	 allowed	 to	
accumulate,	 ammonia	 is	 toxic	
to	 fish	 and	 can	 be	 detrimental	 to	 any	 fish	
production	system.	Once	ammonia	reaches	
toxic	 levels,	 fish	 are	 incapable	 of	 extract-
ing	 needed	 energy	 from	 their	 feed.	 If	 the	
ammonia	gets	to	a	high	enough	quantity,	the	
fish	 will	 eventually	 become	 slow,	 lethargic	
and	eventually	succumb	to	these	high	levels	
resulting	in	possible	death.
In	 a	 properly	 managed	 aquaculture	 pond	
setting,	 ammonia	 seldom	 accumulates	 to	
lethal	concentrations.	However,	ammonia	can	
have	negative	effects	that	don’t	result	in	death	
but	 cause	 reduced	 growth	 rates,	 poor	 feed	
conversion,	 and	 reduced	 disease	 resistance.	
So,	 even	 though	 the	 fish	 don’t	 die	 directly	
from	ammonia	toxicity,	it	can	affect	the	sys-
tem	 in	 other	 ways	 and	 ultimately	 affect	 the	
overall	crop.
Ammonia dynamics
A	single	one-time	measurement	of	ammo-
nia	 concentration	 provides	 only	 a	 snapshot	
in	 time	 that	 the	 sample	 is	 measured.	 The	
processes	 that	 produce,	 remove	 and	 trans-
form	ammonia	are	complex	and	can	change	
throughout	 the	 year.	 Sampling	 at	 different	
times	and	logging	that	data	can	provide	more	
detailed,	accurate	information	into	the	proc-
esses	that	affect	your	aquaculture	system.	
The	 main	 source	 of	 ammonia	 is	 simply	
through	 fish	 excretion.	 The	 excrement	 rate	
is	 directly	 related	 to	 the	 feeding	 rate	 and	
the	protein	level	in	the	feed	being	used.	As	
the	 feed’s	 protein	 is	 broken	 down	 in	 the	
fish’s	body,	some	of	the	nitrogen	is	used	to	
form	protein	(muscle),	energy,	and	excreted	
through	the	gills	as	ammonia.	The	protein	in	
feed	is	the	ultimate	source	of	most	ammonia	
in	ponds	where	fish	are	fed.
Another	 main	 source	 of	 ammonia	 is	 the	
diffusion	from	the	ponds	sediment	itself.	Large	
amounts	of	organic	matter	are	produced	by	
algae	or	added	to	ponds	as	feed.	Fecal	solids	
and	 dead	 algae	 settle	 to	 the	 pond	 bottom	
and	begin	the	process	of	decomposition.	This	
process	 produces	 ammonia	 which	 diffuses	
from	 the	 sediment	 bottom	 into	 the	 water	
column.
Ammonia sinks
Luckily,	there	are	a	couple	processes	that	
also	result	in	the	loss	or	transformation	of	
ammonia.	 The	 most	 important	 process	 is	
the	loss	of	ammonia	through	the	uptake	by	
algae	and	other	plants.	Plants	use	the	nitro-
gen	as	a	nutrient	for	growth.	Photosynthesis	
acts	 like	 a	 sponge	 for	 ammonia	 uptake	 so	
overall	plant	or	algae	growth	in	the	ponds	
can	help	use	up	ammonia.	Of	course,	exces-
sive	plant	growth	can	have	an	effect	on	the	
diurnal	 cycles	 of	 dissolved	 oxygen	 (DO)	
levels	 causing	 DO	 to	 go	 very	 low	 during	
nighttime	hours.
The	 other	 ammonia	 removal	 process	
is	 the	 transformation	 of	 ammonia	 through	
nitrification.	 Two	 main	 types	 of	 bacteria,	
Nitrosomonas	 and	 Nitrobacteria,	 effectively	
oxidize	ammonia	in	a	two-step	process.	First	
they	convert	ammonia	to	nitrite	(NO2-)	and	
then	to	nitrate	(NO3-).	Essentially,	nitrification	
is	a	process	of	nitrogen	compound	oxidation	
(effectively,	loss	of	electrons	from	the	nitrogen	
atom	to	the	oxygen	atoms).
Several	factors	affect	nitrification	rates	and	
understanding	 these	 and	 measuring	 ammonia	
at	 various	 times	 will	 provide	 a	 much	 better	
understanding	for	clear	management	decisions.	
Ammonia	 concentration,	 temperature,	 and	
dissolved	oxygen	concentration	all	play	a	major	
role.	During	summer,	ammonia	concentration	
is	typically	very	low	and	so	nitrification	rates	are	
also	very	low	along	with	bacterial	populations	
to	 handle	 excess	 ammonia.	 During	 winter,	
low	temperature	suppresses	microbial	activity.	
However,	during	the	spring	and	fall,	ammonia	
concentrations	 and	 temperature	 are	 at	 levels	
that	favour	higher	nitrification	rates.	Spring	and	
fall	 have	 common	 peaks	 in	 nitrite	 concentra-
tions	in	many	fish	ponds.
Greatest likelihood of
ammonia problems
The	U.S.	Environmental	Protection	Agency	
(EPA)	 has	 established	 three	 kinds	 of	 criteria	
(one	 acute	 and	 two	 chronic)	 for	 ammonia	
(nitrogen),	based	on	the	duration	of	exposure.	
The	acute	criterion	is	a	1-hour	average	expo-
sure	 concentration	 and	 is	 a	 function	 of	 pH.	
One	 chronic	 criterion	 is	 the	 30-day	 average	
concentration	 and	 is	 a	 function	 of	 pH	 and	
temperature.	 The	 other	 chronic	 criterion	 is	
the	highest	4-day	average	within	the	30-day	
period	 and	 is	 calculated	 as	 2.5	 times	 the	
30-day	 chronic	 criterion.	 The	 EPA	 criteria	
help	 determine	 when	 ammonia	 might	 be	 a	
problem.
Ammonia	 levels	 are	 heavily	 affected	 by	
changes	in	pH	and	temperature.	Free	ammo-
nia	 is	 the	 toxic	 part	 of	 the	 Total	 Ammonia	
Nitrogen	(TAN).	Above	pH	of	8.0	the	toxicity	
of	the	TAN	rapidly	rises.	Source	downloaded	
from	www.aquaworldaquarium.com
Contrary	 to	 common	 assumptions,	
ammonia	concentration	tends	to	be	greater	
during	 the	 winter	 (2.5-4.0	 mg/l	 or	 higher)	
than	during	summer	(~0.5	mg/l).	The	30-day	
chronic	 criterion	 for	 ammonia	 (nitrogen)	
in	 winter	 ranges	 from	 about	 1.5-3.0	 mg/l,	
depending	on	pH.	Ammonia	concentrations	
may	 exceed	 these	 concentrations	 during	
the	winter	months	during	a	time	when	fish	
Understanding ammonia in
aquaculture ponds
by Patrick Higgins, YSI, a xylem brand, USA
22 | InternatIOnal AquAFeed | September-October 2013
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immune	 systems	 are	 suppressed	 due	 to	
lower	temperatures.
Another	 concern	 for	 ammonia	 problems	
occurs	 after	 a	 crash	 in	 the	 algae	 community.	
Rapid	 decomposition	 of	 dead	 algae	 reduces	
the	DO	concentration	and	pH	and	increases	
ammonia	 and	 carbon	 dioxide	 concentrations.	
After	an	algae	crash,	ammonia	concentrations	
can	 increase	 to	 6-8	 mg/l	 and	 the	 pH	 can	
decline	to	7.8-8.0.	The	4-day	chronic	criterion	
ranges	from	about	2.0	mg/l	at	8.0	pH	to	about	
3.0	mg/l	at	7.8	pH.	Therefore,	ammonia	con-
centration	 after	 the	 crash	 of	 an	 algae	 bloom	
may	exceed	the	4-day	chronic	criterion.
Daily	 variation	 in	 the	 concentration	
of	 toxic,	 unionized	 ammonia	 depends	 on	
changes	in	pH	from	photosynthesis	and,	to	
a	 much	 lesser	 extent,	 temperature.	 In	 the	
late	summer	or	early	fall,	ammonia	concen-
tration	begins	to	increase	but	daily	changes	
in	pH	remain	large.	In	these	situations,	fish	
may	 be	 exposed	 to	 ammonia	 concentra-
tions	that	exceed	the	acute	criterion	for	a	
few	 hours	 each	 day.	 If	 late	 afternoon	 pH	
is	 about	 9.0,	 the	 acute	 criterion	 is	 about	
1.5-2.0	mg/l	total	ammonia-nitrogen.	These	
concentrations	during	the	summer	are	typi-
cally	less	than	0.5	mg/l,	so	fish	are	unlikely	
to	 be	 stressed	 if	 the	 late	 afternoon	 pH	 is	
less	than	9.0.
Ammonia management
Even	though	practical	ammonia	manage-
ment	actions	may	be	limited	in	a	large	pond	
aquaculture	 setting	 there	 may	 be	 some	
ways	to	reduce	ammonia	levels	but	others	
may	exacerbate	the	situation	-	no	method	
is	a	complete	long-term	solution	in	and	of	
itself.
Reduce feeding rates
Since	 excess	 feed	 and	 fish	 excretion	 are	
the	 main	 culprits	 of	
ammonia	 build	 up	
it	 seems	 reasonable	
to	 feed	 only	 what	
the	 fish	 need.	 This	
is	 not	 a	 short	 term	
fix	 but	 better	 man-
aged	 over	 time	 to	
help	 keep	 ammonia	
levels	 reasonable.	
Using	 instrumen-
tation	 such	 as	 the	
YSI	 5200A	 or	 5400	
continuous	monitors	
with	 built	 in	 Feed	
SmartTM	 software	
can	 easily	 manage	
feed	 delivery	 rates	
based	on	user	input.
Increase
aeration
Aeration	 can	 be	
ineffective	 at	 reduc-
ing	 overall	 pond	
ammonia	 concen-
trations	 due	 to	 the	
relatively	 small	 area	
of	 the	 pond	 being	
aerated.	However,	it	
does	 increase	 DO	
levels	 causing	 fish	
to	 be	 less	 stressed.	
Avoid	 vigorous	
aeration	 to	 prevent	
stirring	 bottom	
sediment	 which	 can	
actually	 increase	
ammonia	concentra-
tions.
Lime
Using	 lime	
agents	 such	 as	
hydrated	 lime	 or	
quick	 lime	 could	
actually	 make	 a	
potentially	 bad	
situation	 much	
worse	 by	 caus-
ing	 an	 abrupt	 and	
large	 increase	 in	
pH.	 Increasing	 pH	
will	 shift	 ammo-
nia	 toward	 the	
form	 that	 is	 toxic	
to	 fish.	 In	 addi-
tion,	 the	 calcium	
in	 lime	 can	 react	
with	soluble	phos-
phorus,	 removing	
it	 from	 water	 and	
making	 it	 unavail-
able	to	algae.
Many	 fish	 ponds	
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ET-233A.indd 1 12/27/12 10:51 AM
September-October 2013 | InternatIOnal AquAFeed | 23
FEATURE
Understanding ammonia in aquaculture ponds
have	sufficient	alkalinity	so	increasing	it	above	
20	mg/l	as	CaCO3	will	not	provide	additional	
benefit.	It	only	shifts	the	distribution	of	ammo-
nia	from	the	toxic	to	the	non-toxic	form	by	
moderating	high	pH	in	the	afternoon	without	
addressing	the	root	causes	of	the	high	ammo-
nia	concentration.
Fertilize with phosphorus
Under	 normal	 pond	 conditions,	 algae	
blooms	are	very	dense	and	the	rate	of	algae	
growth	 is	 limited	 by	 the	 availability	 of	 light,	
not	nutrients	such	as	phosphorus	or	nitrogen.	
Adding	 phosphorus	 does	 little	 to	 reduce	
ammonia	 concentrations	 because	 algae	 are	
already	growing	as	fast	as	possible	under	the	
natural	conditions	in	the	pond.
Adding bacterial amendments
Common	aquatic	bacteria	are	an	essen-
tial	part	of	the	constant	cycling	of	ammonia	
in	pond	ecosystems.	Typical	pond	manage-
ment	creates	very	favourable	conditions	for	
bacterial	growth.	This	growth	and	activity	is	
limited	 more	 by	 the	 availability	 of	 oxygen	
and	 by	 temperature	 than	 by	 the	 number	
of	bacterial	cells.	In	most	amendments,	the	
most	 abundant	 bacteria	 are	 responsible	
for	 the	 decomposition	 of	 organic	 matter.	
Therefore,	if	bacterial	amendments	acceler-
ate	 the	 decomposition	 of	 organic	 matter,	
the	opposite	deleterious	effect	could	occur	
and	ammonia	levels	could	actually	increase!
Measuring ammonia
Research	 has	 indicated	 that	 brief	 daily	
exposure	 to	 ammonia	 concentrations	 far	
higher	 than	 those	 measured	 in	 commercial	
ponds	does	not	affect	fish	growth.	However,	
there	are	circumstances	when	it	is	definitely	
worthwhile	to	monitor	ammonia	levels.
Taking	 ammonia	 readings	 with	 an	 instru-
ment	like	the	YSI	Professional	Plus	and	saving	
the	 data	 and	 viewing	 trends	 with	 desktop	
software	can	provide	valuable	information	in	
managing	your	aquaculture	operation,	stock-
ing	rates,	issues	with	overfeeding	and	more.
In	 the	 south	 of	 the	 USA,	 for	 instance,	
ammonia	concentrations	in	most	ponds	usu-
ally	 start	 increasing	 in	 September	 and	 reach	
a	 peak	 around	 mid-October	 generally	 5-6	
weeks	 after	 the	 last	 period	 of	 high	 feeding	
rates.	About	2-4	weeks	later	nitrite	concen-
trations	 will	 also	 peak.	 This	 is	 a	 generalised	
pattern	 and	 doesn’t	 occur	 in	 every	 pond.	
Ammonia	 or	 nitrite	 problems	 can	 occur	
with	variable	intensity	at	any	time,	especially	
between	September	and	March	and	measur-
ing	will	help	indicate	this	pattern.
Ammonia	 should	 be	 measured	 after	 the	
crash	of	an	algae	bloom	and	at	least	weekly	
in	cooler	months	of	the	year	to	help	identify	
trends	and	potential	problems	not	only	with	
ammonia	but	also	nitrite.
In	 summary,	 ammonia	 levels	 are	 difficult	 to	
correct	quickly	and	effectively,	especially	in	large	
ponds,	 so	 measuring	 and	 understanding	 your	
ponds	natural	ability	to	correct	for	high	ammonia	
and	 nitrite	 levels	 can	 alleviate	 high	 concentra-
tions.	After	seeing	the	difficulty	in	correcting	high	
ammonia	levels,	measuring	for	ammonia	can	give	
a	good	indication	of	high	nitrite	levels	and	allow	
operators	to	effectively	use	salt	to	help	protect	
fish	against	nitrite	toxicosis.	Extra	vigilance	after	an	
algae	crash	is	also	warranted.	Ammonia	levels	will	
typically	fall	back	to	‘normal’	levels	again	once	the	
algae	becomes	re-established.
The	primary	key	to	proper	ammonia	manage-
ment	is	to	use	fish	culture	practices	that	minimize	
the	 likelihood	 of	 such	 problems.	 This	 means	
stocking	fish	at	a	reasonable	density,	harvesting	as	
often	as	practical	to	keep	the	standing	crop	from	
being	too	large,	and	using	good	feeding	practices	
that	maximize	the	proportion	of	feed	consumed	
by	the	fish	to	help	eliminate	excess.
Measuring	 for	 ammonia	 and	 recognising	
trends	 and	 levels	 for	 your	 operation	 is	 the	
easiest	 way	 to	 understand	 good	 operational	
decisions	for	your	facility.	Correcting	ammonia	
problems	 can	 be	 difficult	 so	 maintaining	 a	
proactive	sampling	programme	can	help	pre-
vent	large	ammonia	and	nitrite	concentrations.
Some	ammonia	test	kits	can	be	time	con-
suming	if	measuring	many	ponds	or	tanks	and	
may	 only	 give	 an	 indication	 or	 an	 ammonia	
range.	 Handheld	 instruments	 with	 pH	 and	
ammonia	sensors	can	give	a	much	faster,	accu-
rate	method	for	understanding	your	system’s	
ammonia	issues	and	leading	to	faster	opera-
tional	decisions	increasing	facility	efficiencies.
References	available	on	request
More InforMatIon:
Email: environmental@ysi.com
Website: www.ysi.com/aquaculture
24 | InternatIOnal AquAFeed | September-October 2013
FEATURE
September-October 2013 | InternatIOnal AquAFeed | 25
FEATURE
SPANISH
LANGUAGE
EDITION
www.aquafeed.co
EDICION
ESPANOLA
www.aquafeed.co.uk
LINKS
•	 See the full issue
•	 Visit the International Aquafeed website
•	 Contact the International Aquafeed Team
•	 Subscribe to International Aquafeed
The potential of
microalgae meals
– in compound feeds for aquaculture
Understanding ammonia
in aquaculture ponds
Volume 16 Issue 5 2013 - sePTemBeR | oCToBeR
INCORPORATING
fIsh fARmING TeChNOlOGy
EXPERT TOPIC
– Salmon
AquaNor event review
Thisdigitalre-printispartoftheSeptember|October2013editionofInternational
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Understanding ammonia in aquaculture ponds

  • 1. September | October 2013 Understanding ammonia in aquaculture ponds The International magazine for the aquaculture feed industry International Aquafeed is published six times a year by Perendale Publishers Ltd of the United Kingdom. All data is published in good faith, based on information received, and while every care is taken to prevent inaccuracies, the publishers accept no liability for any errors or omissions or for the consequences of action taken on the basis of information published. ©Copyright 2013 Perendale Publishers Ltd.All rights reserved.No part of this publication may be reproduced in any form or by any means without prior permission of the copyright owner. Printed by Perendale Publishers Ltd. ISSN: 1464-0058 INCORPORATING f ish farming technolog y
  • 2. REAL BREWERS’YEAST “Made inGermany” For Leiber`s specialty yeast products, “Made in Germany”is a seal of quality. Multibiotic effect of Leiber yeast - vitality, health and performance for fish. Leiber GmbH · Hafenstraße 24, 49565 Bramsche, Germany · Tel +49 (0) 5461 9303-0 · Fax +49 (0) 5461 9303-28 · www.leibergmbh.de · info@leibergmbh.de THE SPECIAL WORLD OF LEIBER YEAST... www.leibergmbh.de
  • 3. U nderstanding ammonia and controlling it is critical in aqua- culture systems. If allowed to accumulate, ammonia is toxic to fish and can be detrimental to any fish production system. Once ammonia reaches toxic levels, fish are incapable of extract- ing needed energy from their feed. If the ammonia gets to a high enough quantity, the fish will eventually become slow, lethargic and eventually succumb to these high levels resulting in possible death. In a properly managed aquaculture pond setting, ammonia seldom accumulates to lethal concentrations. However, ammonia can have negative effects that don’t result in death but cause reduced growth rates, poor feed conversion, and reduced disease resistance. So, even though the fish don’t die directly from ammonia toxicity, it can affect the sys- tem in other ways and ultimately affect the overall crop. Ammonia dynamics A single one-time measurement of ammo- nia concentration provides only a snapshot in time that the sample is measured. The processes that produce, remove and trans- form ammonia are complex and can change throughout the year. Sampling at different times and logging that data can provide more detailed, accurate information into the proc- esses that affect your aquaculture system. The main source of ammonia is simply through fish excretion. The excrement rate is directly related to the feeding rate and the protein level in the feed being used. As the feed’s protein is broken down in the fish’s body, some of the nitrogen is used to form protein (muscle), energy, and excreted through the gills as ammonia. The protein in feed is the ultimate source of most ammonia in ponds where fish are fed. Another main source of ammonia is the diffusion from the ponds sediment itself. Large amounts of organic matter are produced by algae or added to ponds as feed. Fecal solids and dead algae settle to the pond bottom and begin the process of decomposition. This process produces ammonia which diffuses from the sediment bottom into the water column. Ammonia sinks Luckily, there are a couple processes that also result in the loss or transformation of ammonia. The most important process is the loss of ammonia through the uptake by algae and other plants. Plants use the nitro- gen as a nutrient for growth. Photosynthesis acts like a sponge for ammonia uptake so overall plant or algae growth in the ponds can help use up ammonia. Of course, exces- sive plant growth can have an effect on the diurnal cycles of dissolved oxygen (DO) levels causing DO to go very low during nighttime hours. The other ammonia removal process is the transformation of ammonia through nitrification. Two main types of bacteria, Nitrosomonas and Nitrobacteria, effectively oxidize ammonia in a two-step process. First they convert ammonia to nitrite (NO2-) and then to nitrate (NO3-). Essentially, nitrification is a process of nitrogen compound oxidation (effectively, loss of electrons from the nitrogen atom to the oxygen atoms). Several factors affect nitrification rates and understanding these and measuring ammonia at various times will provide a much better understanding for clear management decisions. Ammonia concentration, temperature, and dissolved oxygen concentration all play a major role. During summer, ammonia concentration is typically very low and so nitrification rates are also very low along with bacterial populations to handle excess ammonia. During winter, low temperature suppresses microbial activity. However, during the spring and fall, ammonia concentrations and temperature are at levels that favour higher nitrification rates. Spring and fall have common peaks in nitrite concentra- tions in many fish ponds. Greatest likelihood of ammonia problems The U.S. Environmental Protection Agency (EPA) has established three kinds of criteria (one acute and two chronic) for ammonia (nitrogen), based on the duration of exposure. The acute criterion is a 1-hour average expo- sure concentration and is a function of pH. One chronic criterion is the 30-day average concentration and is a function of pH and temperature. The other chronic criterion is the highest 4-day average within the 30-day period and is calculated as 2.5 times the 30-day chronic criterion. The EPA criteria help determine when ammonia might be a problem. Ammonia levels are heavily affected by changes in pH and temperature. Free ammo- nia is the toxic part of the Total Ammonia Nitrogen (TAN). Above pH of 8.0 the toxicity of the TAN rapidly rises. Source downloaded from www.aquaworldaquarium.com Contrary to common assumptions, ammonia concentration tends to be greater during the winter (2.5-4.0 mg/l or higher) than during summer (~0.5 mg/l). The 30-day chronic criterion for ammonia (nitrogen) in winter ranges from about 1.5-3.0 mg/l, depending on pH. Ammonia concentrations may exceed these concentrations during the winter months during a time when fish Understanding ammonia in aquaculture ponds by Patrick Higgins, YSI, a xylem brand, USA 22 | InternatIOnal AquAFeed | September-October 2013 FEATURE
  • 4. Innovations for a better world. Bühler AG, Feed & Biomass, CH-9240 Uzwil, Switzerland, T +41 71 955 11 11, F +41 71 955 28 96 fu.buz@buhlergroup.com, www.buhlergroup.com Fatten up your bottom line. Bühler high-performance animal and aqua feed production systems are used by leading companies around the world. These producers know they can rely not just on the technology itself, but also on the support that accompanies it. A service combining local presence with global expertise both lowers feed mill operating costs and increases capacity utilization. To find out more, visit www.buhlergroup.com
  • 5. immune systems are suppressed due to lower temperatures. Another concern for ammonia problems occurs after a crash in the algae community. Rapid decomposition of dead algae reduces the DO concentration and pH and increases ammonia and carbon dioxide concentrations. After an algae crash, ammonia concentrations can increase to 6-8 mg/l and the pH can decline to 7.8-8.0. The 4-day chronic criterion ranges from about 2.0 mg/l at 8.0 pH to about 3.0 mg/l at 7.8 pH. Therefore, ammonia con- centration after the crash of an algae bloom may exceed the 4-day chronic criterion. Daily variation in the concentration of toxic, unionized ammonia depends on changes in pH from photosynthesis and, to a much lesser extent, temperature. In the late summer or early fall, ammonia concen- tration begins to increase but daily changes in pH remain large. In these situations, fish may be exposed to ammonia concentra- tions that exceed the acute criterion for a few hours each day. If late afternoon pH is about 9.0, the acute criterion is about 1.5-2.0 mg/l total ammonia-nitrogen. These concentrations during the summer are typi- cally less than 0.5 mg/l, so fish are unlikely to be stressed if the late afternoon pH is less than 9.0. Ammonia management Even though practical ammonia manage- ment actions may be limited in a large pond aquaculture setting there may be some ways to reduce ammonia levels but others may exacerbate the situation - no method is a complete long-term solution in and of itself. Reduce feeding rates Since excess feed and fish excretion are the main culprits of ammonia build up it seems reasonable to feed only what the fish need. This is not a short term fix but better man- aged over time to help keep ammonia levels reasonable. Using instrumen- tation such as the YSI 5200A or 5400 continuous monitors with built in Feed SmartTM software can easily manage feed delivery rates based on user input. Increase aeration Aeration can be ineffective at reduc- ing overall pond ammonia concen- trations due to the relatively small area of the pond being aerated. However, it does increase DO levels causing fish to be less stressed. Avoid vigorous aeration to prevent stirring bottom sediment which can actually increase ammonia concentra- tions. Lime Using lime agents such as hydrated lime or quick lime could actually make a potentially bad situation much worse by caus- ing an abrupt and large increase in pH. Increasing pH will shift ammo- nia toward the form that is toxic to fish. In addi- tion, the calcium in lime can react with soluble phos- phorus, removing it from water and making it unavail- able to algae. Many fish ponds ® Corporate offiCe P.O. Box 8 • 100 Airport Road Sabetha, KS 66534, USA Phone: 785-284-2153 Fax: 785-284-3143 extru-techinc@extru-techinc.com www.extru-techinc.com BREAKTHROUGH in Aquafeed Technology Take this opportunity to visit www.extru-techinc.com/at to see the next level in aquafeed technology. demAnd GEnUinEExTRU-TEcH Oem PARTS Many leading aquafeed manufacturers in the industry count on Extru-Tech to engineer the perfect aquafeed production solution. industry leading equipment and engineered production advantages will give you the upper hand over the competition. could you use a cost effective improvement in performance and finished product quality? contact one of the Aquafeed consultants at Extru-Tech today at 785-284-2153. ET-233A.indd 1 12/27/12 10:51 AM September-October 2013 | InternatIOnal AquAFeed | 23 FEATURE
  • 7. have sufficient alkalinity so increasing it above 20 mg/l as CaCO3 will not provide additional benefit. It only shifts the distribution of ammo- nia from the toxic to the non-toxic form by moderating high pH in the afternoon without addressing the root causes of the high ammo- nia concentration. Fertilize with phosphorus Under normal pond conditions, algae blooms are very dense and the rate of algae growth is limited by the availability of light, not nutrients such as phosphorus or nitrogen. Adding phosphorus does little to reduce ammonia concentrations because algae are already growing as fast as possible under the natural conditions in the pond. Adding bacterial amendments Common aquatic bacteria are an essen- tial part of the constant cycling of ammonia in pond ecosystems. Typical pond manage- ment creates very favourable conditions for bacterial growth. This growth and activity is limited more by the availability of oxygen and by temperature than by the number of bacterial cells. In most amendments, the most abundant bacteria are responsible for the decomposition of organic matter. Therefore, if bacterial amendments acceler- ate the decomposition of organic matter, the opposite deleterious effect could occur and ammonia levels could actually increase! Measuring ammonia Research has indicated that brief daily exposure to ammonia concentrations far higher than those measured in commercial ponds does not affect fish growth. However, there are circumstances when it is definitely worthwhile to monitor ammonia levels. Taking ammonia readings with an instru- ment like the YSI Professional Plus and saving the data and viewing trends with desktop software can provide valuable information in managing your aquaculture operation, stock- ing rates, issues with overfeeding and more. In the south of the USA, for instance, ammonia concentrations in most ponds usu- ally start increasing in September and reach a peak around mid-October generally 5-6 weeks after the last period of high feeding rates. About 2-4 weeks later nitrite concen- trations will also peak. This is a generalised pattern and doesn’t occur in every pond. Ammonia or nitrite problems can occur with variable intensity at any time, especially between September and March and measur- ing will help indicate this pattern. Ammonia should be measured after the crash of an algae bloom and at least weekly in cooler months of the year to help identify trends and potential problems not only with ammonia but also nitrite. In summary, ammonia levels are difficult to correct quickly and effectively, especially in large ponds, so measuring and understanding your ponds natural ability to correct for high ammonia and nitrite levels can alleviate high concentra- tions. After seeing the difficulty in correcting high ammonia levels, measuring for ammonia can give a good indication of high nitrite levels and allow operators to effectively use salt to help protect fish against nitrite toxicosis. Extra vigilance after an algae crash is also warranted. Ammonia levels will typically fall back to ‘normal’ levels again once the algae becomes re-established. The primary key to proper ammonia manage- ment is to use fish culture practices that minimize the likelihood of such problems. This means stocking fish at a reasonable density, harvesting as often as practical to keep the standing crop from being too large, and using good feeding practices that maximize the proportion of feed consumed by the fish to help eliminate excess. Measuring for ammonia and recognising trends and levels for your operation is the easiest way to understand good operational decisions for your facility. Correcting ammonia problems can be difficult so maintaining a proactive sampling programme can help pre- vent large ammonia and nitrite concentrations. Some ammonia test kits can be time con- suming if measuring many ponds or tanks and may only give an indication or an ammonia range. Handheld instruments with pH and ammonia sensors can give a much faster, accu- rate method for understanding your system’s ammonia issues and leading to faster opera- tional decisions increasing facility efficiencies. References available on request More InforMatIon: Email: environmental@ysi.com Website: www.ysi.com/aquaculture 24 | InternatIOnal AquAFeed | September-October 2013 FEATURE
  • 8. September-October 2013 | InternatIOnal AquAFeed | 25 FEATURE SPANISH LANGUAGE EDITION www.aquafeed.co EDICION ESPANOLA
  • 9. www.aquafeed.co.uk LINKS • See the full issue • Visit the International Aquafeed website • Contact the International Aquafeed Team • Subscribe to International Aquafeed The potential of microalgae meals – in compound feeds for aquaculture Understanding ammonia in aquaculture ponds Volume 16 Issue 5 2013 - sePTemBeR | oCToBeR INCORPORATING fIsh fARmING TeChNOlOGy EXPERT TOPIC – Salmon AquaNor event review Thisdigitalre-printispartoftheSeptember|October2013editionofInternational Aquafeed magazine. Content from the magazine is available to view free-of-charge, both as a full online magazine on our website, and as an archive of individual features on the docstoc website. Please click here to view our other publications on www.docstoc.com. To purchase a paper copy of the magazine, or to subscribe to the paper edition please contact our Circulation and Subscriptions Manager on the link above. INFORMATION FOR ADVERTISERS - CLICK HERE