International Journal of Geosciences, 2013, 4, 46-53 Published Online September 2013 (
Copyright © 2013 SciRes. IJG
Relationships of Dissolved Oxygen with Chlorophyll-a and
Phytoplankton Composition in Tilapia Ponds
Kornkanok Kunlasak1,2, Chanagun Chitmanat1, Niwooti Whangchai1,
Jongkon Promya1, Louis Lebel2
1Faculty of Fisheries Technology and Aquatic Resources, Maejo University, Chiang Mai, Thailand
2Unit for Social and Environmental Research (USER) Faculty of Social Science, Chiang Mai University, Ch iang Mai, Thailand
Received July 2013
This study investigated the relationships among the parameters of dissolved oxygen, chlorophyll-a and phytoplankton
composition in tilapia ponds. Each pond (a total of 18 ponds) was sampled once in the dry, winter season between J an-
uary and March and again early in the rainy season between May and June. The data were analyzed by examining cor-
relations among parameters as affected by season, altitude and culture system. Observations were made at sites located
in 5 selected provinces of northern Thailand: Chiangrai, Chiangmai, Phayao, Lampang and Nakornsawan. Mean eleva-
tion of these areas range from 25 to 582 meters above sea level (masl) and were categorized into low (<400 masl) and
high (>400 masl) elevation sites. Ponds were 0.8 - 2.0 m deep, 0.16 - 0.64 ha in area and could be further categorized
into high and low input systems.Mean air temperature in winter ranged between 16.5˚C - 35.8˚C while mean water
temperature ranged between 25.5˚C - 27.1˚C. In rainy season, air temperature ranged between 22.0˚C - 3 7. 3˚C an d wa-
ter temperature ranged between 29.4˚C - 31.8˚C. The amount of chlorophyll-a in both seasons were comparable (p >
0.05), but chlorophyll-a in high input system was significantly higher (p < 0.05) than in low input ponds. Only weak
correlation was found between chlorophyll-a, DOmax and DOmin. Multifactor-ANOVA was used to analyze the differ-
ence of total bacteria and filamentous cyanobacteria in ponds based upon elevation, culture systems and season. Result
shows that there is a significant interaction observed between elevation, culture system and season (p < 0.05). Species
diversity and composition of phytoplankton in fish ponds in 2 seasons revealed the presence of 90 genera of phytop-
lankton under all 7 divisions. Divisions Chlorophyta and Cyanophyta had the most number of genera identified in both
seasons with Pediastrum spp., and Scendesmus spp., and Anabaena spp. as dominant genera/genus, respectively.
Keywords: Dissolved O xygen; Chlorophyll-a; Phytoplankton Composition; Tilapia Ponds; Elevation, Season
1. Introduction
Increased demand for high protein food and apparent
declines in capture fisheries together have helped drive
rapid expansion of the aquaculture industry in the past
two decades. Th e aquacultur e industry howev er is facing
challenges such as high cost of inputs and climatic
changes. Climate effect such as increase in temperature is
observed to increase disease transmission, deplete oxy-
gen, increase incidence of harmful algal blooms in ponds
to mention a few [1].
Tilapia culture is one of the major aquaculture indus-
tries in Thailand with river cage and earthen pond cul-
tures were both practiced. However, some tilapia cage
farmers have switched from river to earthen pond due to
difficulties with extreme water flows and poor water
quality. There are substantial differences in tilapia cul-
ture systems among places depending on various con-
straints and opportunities such as topography (lowland
and upland) and availability of water and alternative nu-
trient inputs [2]. Elevation above sea level, for instance,
influences air and water temperature in pond culture [3].
Physical, chemical and biological water quality in fish
pond ecosystem influences growth and survival rates as
well as reproduction and likelihood of disease infection
[4]. Dissolved oxygen (DO), in particular, is an important
factor for fish respiration and phytoplankton dynamics.
DO content typically correlates with phytoplankton den-
sity in fish ponds. Main tenance of phytoplank ton popula-
tions at desired levels is an important but difficult aspect
of fish pond management. Many fish culture manuals
stress that an algal bloo m must be maintained to improve
oxygen levels, to prevent macrophyte growth, and to
provide natural foods, either directly or indirectly, for
fish in the pond [5-7]. At the same time, however, uncon-
trolled algal growth causes many serious problems for
aquaculturists [8]. Thus, proper management of phytop-
Copyright © 2013 SciRes. IJG
lankton growth is a major goal of modern pond aquacul-
ture [7-10].
While phytoplankton affects water quality in several
ways [7,8], the difficulty and importance of managing
phytoplankton stem primarily from the complex rela-
tionship between algal dynamics and dissolved oxygen
levels. Phytoplankton are the major source of dissolved
oxygen in fish ponds as well as—directly as consumers
and indirectly as the source of detritus upon which most
bacterial respiration is b ased—the major sink for oxygen
[11,12]. Dissolved oxygen levels depend primarily on the
relative magnitudes of photosynthetic oxygen generation
and total plankton respiration [13]. Given the complexity
of this relationship and the importance of dissolved oxy-
gen to aquacultural production [14], the interaction be-
tween dissolved oxygen and phytoplankton biomass
should be e xamined in de t a il.
Water quality in aquaculture ponds is influenced by
management and other external factors such as culture
system, stocking densities, water exchange practices and
sources, and fertilizer application. The main objective of
this research was to determine the association between
chlorophyll-a, phytoplankton composition, and dissolved
oxygen in tilapia ponds from different culture systems in
winter and rainy seasons. This information will be then
used to develop techniques to manage phytoplankton and
dissolved ox yge n dynamics in fish ponds .
2. Materials and Methods
2.1. Study Sites
In this study, data was collected in the dry, winter season,
between January and March and in the early rainy season
between May and June 2013. Observations were made in
18 ponds at sites located in 5 selected provinces of
northern Thailand: Chiangrai, Chiangmai, Phayao, Lam-
pang and Nakornsawan. Mean elevation of these areas
range from 25 to 582 meters above sea level (masl).
Ponds were 08 - 2.0 m deep and 0.16 - 0.64 ha in size at
different elevations above sea level (low: <400 masl and
high: >400 mas l) and employed different cultu re systems:
high input (high load of nutrient resulting either from
intensive feed ing or from manure fertilization) and low
input (low load of nutrient where feeding was sporadic).
2.2. Water Sampling and Analysis
Pond water samples were assessed to determine levels of
algal biomass, total bacteria and other water quality pa-
rameters. Dissolved oxygen was monitored in situ along
with pH, temperature, turbidity and conductivity using
the multi-meter TOA DKK WQC-22A (Japan). Water
samples were collected for nutrient analyses (nitrate-N,
nitrite-N, total ammonia-N, and orthophosphate-P) and
chlorophyll-a determination in the laboratory following
standard methods [15]. For hydro-biological analysis,
phytoplankton was sampled by filtration of 5-L pond
water with a net of 10-μm mesh. Samples were concen-
trated in a 30-mL plastic bottle and immediately pre-
served with 1 mL Lugol’s solution. Species and count of
phytoplankton were determined using an Olympus BH2
microscope with the aid of a 1000 oil immersion objec-
tive. Total bacterial analysis was done using the pour
plate technique as described in ISO, 1999 and SCA, 2002
2.3. Statistical Analysis
Analysis of Variance (ANOVA) was used to compare
water pond parameters across the two seasons and eleva-
tion groups. Paired sample T-test was used to compare
the differences of water quality variables between the
two seasons, elevation groups and culture systems.
3. Results and Discussion
3.1. Effect of Season on the Relationship between
Chlorophyll-a and Dissolved Oxygen
Monitoring of tilapia ponds was carried out during winter
and early rainy season. Mean chlorophyll-a concentra-
tions, DOmax and DOmin were comparable between the
two seasons (Tabl e 1 ). Mean DO ( max and min) concen-
trations were not significantly different between the two
seasons. A significant negative correlation was found
between chlorophyll-a and DOmin in both seasons (Fig-
ure 1). There was no association with DOmax. The fre-
quency of DOmin levels b elow 1-ppm threshold value (red
line in figures) were comparable between the two sea-
As a general rule of thumb, DO level in ponds corre-
lates with the amount of chlorophyll-a which results from
phytoplankton biomass. In water bodies when the
amount of phytoplankton increases, the amount of chlo-
rophyll-a increases as well [18] and so does DO due to
algal photosynthesis during daylight (positive relation-
ship with DOmax). However, as phytoplankton biomass
Table 1. Means (±SD) of chl orophyll-a, DOmax and DOmin in
winter and rainy season.
Parameter Season
Winter Rainy
Mean Chlorophyll-a (µg·L1) 177.8 ± 174.0ns 204.8 ± 220.1ns
Mean DO max (mg·L1) 7.78 ± 1.94ns 7.59 ± 4.60ns
Mean DO min (mg·L1) 1.96 ± 2.19ns 1.12 ± 1.68ns
Values with the same letter superscripts in rows are not significantly differ-
ent (P > 0.05) .
Copyright © 2013 SciRes. IJG
Figure 1. Correlation of DOmax/DOmin versus chlorophyll-a for winter (a) and rainy (b) season.
increases, respiration during nighttime can deplete DO
concentrations to critical values (negative relationship
with DOmin). The lack of relationship of chlorophyll-a
with DOmax and significant negative association with
DOmin in both seasons could be explained that DO was
affected not only by algal photosynthesis but also by aq-
uatic respiration, oxidative decomposition of organic
compounds (from fish and animal wastes), water ex-
change rate and artificial pond aeration (in the case of
commercial ponds). Differences in culture practices
among ponds surveyed in the study may have also influ-
enced relationships and will now be considered in more
3.2. Effect of Culture System on the Relationship
between Chlorophyll-a and Dissolved
Mean chlorophyll-a concentration was significantly low-
er in tilapia ponds which adopt low input culture system
compared to those that receive high inputs (Table 2).
Mean DO (max and min) concentrations of ponds re-
ceiving low and high inputs were not significantly dif-
ferent. A significant positive correlation between chlo-
rophyll-a and DOmax was observed in high input ponds
but not low-input ponds (Figure 2). A significant nega-
tive correlation of chlorophyll-a with DOmin was found in
low-input ponds, bu t not high input ponds (Figure 2).
High input ponds, which comprise both surveyed com-
mercial and integrated fish farming ponds, are expected
Table 2. Means (±SD) of chlorophyll-a, DOmax and DOmin in
high and low input-based culture systems.
Parameter Culture System
High input L ow input
Chlorophyll-a (µg·L1) 273.0 ± 199.3ª 45.1 ± 26.8
DO max (mg·L1) 8.20 ± 3.46ns 6.78 ± 3.10 ns
DO min (mg·L1) 0.65 ± 1.22 ns 3.20 ± 2.08 ns
Values wit h the same letter superscripts in rows are no t significantl y differ-
ent (P > 0.05) .
to have higher chlorophyll-a concentrations compared to
low input (su bsistence) ponds due to their higher nutrient
loads. Commercial tilapia farms usually adopt intensive
culture system of production with high stocking rates
which rely heavily on th e use of commercial f eeds rather
than on natural food. As fish waste and uneaten feed en-
ter the pond system, nutrients accumulate in the bottom,
released into the water and taken up by phytoplankton
bloom. Similarly, integrated ponds (with p ig and chicken)
produce high loads of nutrients from manure fertilization
for the purpose of producing natural food for the fish.
The utilization of organic manure as the principal nu-
trient input to the pon d is a traditional management pra c-
tice in freshwater fish farming in Thailand.
In high input culture system, changes in DOmax slightly
follow adjustments in chlorophyll-a concentration show-
ing a weak positive relationship. However, the negative
correlation observed in low input culture system between
Copyright © 2013 SciRes. IJG
Figure 2. Correlation of DOmax/DOmin versus chlorophyll-a for hi gh input (a) and low input ( b) culture syst em.
chlorophyll-a and DOmax contradicts the general rule and
no explanation can currently be found with regards to
this result.
3.3. Effect of Elevation on the Relationship
between Chlorophyll-a and Dissolved
Mean chlorophyll-a, mean DOmax and DOmin in ponds
surveyed from low elevation sites were not significantly
different from ponds in high elevation as shown (Table
3). In low elevation sites, chlorophyll-a and DOmax was
positively correlated with each other, whilst chloro-
phyll-a and DOmin were correlated negatively (Figure 3).
In high elevation sites chlorophyll-a was significantly
negatively correlated with DOmin (Figure 3).
The present study covered a wide range of tilapia pro-
duction systems (commercial, integrated and subsistence)
at low elevation sites. Water quantity is not a major con-
straint, but these areas may acquire other impacts making
changes to culture systems e.g. floods, capital cost or
market access. These impacts may cause farmers to
switch from commercial to integrated system (fish and
pig or chicken/multiple fish species) to reduce production
cost but the quality of tilapia maybe affected in terms of
off-flavor due to uncontrolled cyanobacterial growth in
high-nutrient waters of an integrated system. The inte-
grated system of culture could blend well with the re-
source-poor small-scale aquaculture farmers especially
Table 3. Means (±SD) of chlorophyll-a, DO max and DO
min at <400 and >400 masl.
Parameter Elevation, masl
<400 >400
Chlorophyll-a (µg·L1) 219.0 ± 222.0ns 155.6 ± 153.1ns
DO max (mg·L1) 7.19 ± 4.28ns 8.27 ± 1.71ns
DO min (mg·L1) 1.00 ± 1.65ns 2.27 ± 2.19ns
Values wit h the same letter superscripts in rows are not significantly differ-
ent (P > 0.05) .
those dependent on aquatic resource for their livelihoods
since this strategy would make them more resilient to
climate variability. On the o ther hand, to resist the impact
of flooding in low elevation sites, the farmer can streng-
then and increase the height of the perimeter dikes. The
farmer can likewise deploy nets on the top of the dykes
so that when a flood occurs, the fish remain in the ponds.
At high elevation sites, it could be the proper area for
subsistence system since water scarcity, fingerlin gs qual-
ity and lower temperature are major conditions.
Higher elevation sites and high input systems were
more likely to have DOmin values below the threshold
level of 1 ppm than at lower elevation sites and low input
systems, respectively (Table 4). Chlorophyll-a in high
input system were significantly higher than in low input
system. Seasonal and elevation differences were not sig-
nificant (Table 4).
Copyright © 2013 SciRes. IJG
Figure 3. Correlation of DOmax/DOmin versus chlorophyll-a for <400 masl (a) and >400 masl (b) sites.
Table 4. Percentage (%) of tilapia ponds with DOmin below t he threshold value (1 ppm) and effect of season, culture system
and elevation on c hlorophyll-a.
Factor Mean Chlorophyll-a (µg ·L1) Number of ponds (%)
Total (n) No. with <1 p p m D O mi n.
Winter 177.8 ± 174.0ns 18 9 50.00
Rainy 204.9 ± 220.1ns 15 10 66.67
Culture system
high input 273.0 ± 199.3ª 22 17 77.27
low input 45.1 ± 26.9 12 2 16.67
<400 218.9 ± 222.0ns 18 13 72.22
>400 155.6 ± 153.1ns 15 6 40.00
Values with different letter superscripts in the column are signifi cantly different (P < 0.05).
3.4. Effect of Elevation, Culture System and
Season on Total Bacterial Load
Mean total bacteria concentration in pond water at high
input system in low elevation sites (<400 masl) was sig-
nificantly higher (P < 0.05) than in high elevation sites
(>400 masl) whilst in low input systems at high elevation
sites mean total bacteria concentration was significantly
higher (P < 0.05) than at low elevation sites (Table 5).
Multifactor-ANOVA was used to evaluate differences
in total bacterial concentration in ponds based upon ele-
vation, culture system and s eason. Significant interaction
among elevation, culture system and season for total
bacteria concentration were observed (Figu re 4).
In general, temperature varies inversely with elevation.
This is one of the reasons why lower bacteria activity
was seen in higher altitude ponds (>400 masl). Mean
Copyright © 2013 SciRes. IJG
Table 5. Total bacteria (×103) (±SD) in ponds at different
elevation i n both culture sys t em .
Culture System Elevation, masl
<400 >400
High input 7.37 ± 5.30ª 1.17 ± 1.11
Low input 0.29 ± 0.16 0.97 ± 0.59ª
Values with different letter superscripts in rows are significantly different (P
< 0.05).
Figure 4. Total bacteria in ponds at different elevation and
culture sy s t em in both seasons.
temperatures at low elevation sites are higher by 2 de-
grees than at high elevation sites. High organic loading
also increased nutrient and bacterial levels in high input
pond systems at <400 masl. Commercial and integrated
culture systems (high input systems) have higher fish
stocking density and feeding rate and therefore the
amount of organic matter and waste (including excess
uneaten feeds) are expectedly high for these systems
which increase bacterial load in water. This could deplete
DO from water during the decomposition of these mate-
rials at the bottom. Farms, especially those which grow
tilapia in commercial ponds like the one in Phayao (>400
masl), use aerators to counteract DO depletion during
However, for low input pond system at high elevation
sites, bacterial level is higher than the hotter low eleva-
tion sites. This observation contr adicts the result obtain ed
for high inp ut pond system. T emperatu re has b een sh own
to be one of the limiting factors for bacterial growth par-
ticularly in relatively low temperatures (<12˚C - 15˚C)
although many of bacteria are adapted to colder envi-
ronment, hence, the result. It is also possible that subsis-
tence ponds in higher altitudes had higher organic matter
content than in lower altitude ponds which could have
significantly contribute to the bacterial load in the water.
3.5. Phytoplankton Density and Effect of
Elevation, Culture System and Season on
Filamentous Cyanobacteria Biomass
For the assessment of diversity and composition of phy-
toplankton in the surveyed ponds, a total of 90 genera of
phytoplankton from 7 divisions were identified covering
the 2 sampling seasons. Divis ion C hl oro phy t a ( 49 ge ne ra,
54.4%) was the most abundant followed by Bacillario-
phyta (13 gene ra, 14.4%), Cyanophyta (10 genera,
11.1%), Cryptophyta (7 genera, 7.8%), Chromophyta (5
genera, 5.6%), Euglenophyta (5 genera, 5.6%), and Pyr-
rhophyt a (1 genus, 1.1% ) whi ch wa s fo und onl y in winte r.
In terms of phytoplankton density, Cyanophyta (cyano-
bacteria) dominated the pond waters in winter whilst
Chlorophyta were the prevalent group during rainy sea-
son. There were no significant differences in total bio-
mass of both Cyanophyta and Chlorophyta between sea-
sons (Figure 5). Among the phytoplankton identified in
the study, Pediastrum spp. and Scendesmus spp., both
chlorophytes, and Anabaena spp., a cyanobacteria, dom-
inated the pond waters.
Mean density of filamentous cyanobacteria was sig-
nificantly higher (P < 0.05) in high input system at low
elevation sites (<400 masl) than in high elevation sites
(>400 masl). However, result for low input system shows
otherwise, where density of filamentous cyanobacteria
was observed to be significantly higher (P < 0.05) at high
elevation sites as opposed to low elevation sites (Table
Figure 5. Phy t opl an kt on densitie s in ponds in 2 seasons.
Table 6. Cell density (×103) (±SD) of filamentous cyanobac-
teria in ponds at different elevation in both culture system.
Culture System Elevation, masl
<400 >400
High input 7.96 ± 5.37ª 1.43 ± 0.1
Low input 0.34 ± 0.16 1.78 ± 0.6ª
Values with different letter superscripts in rows are significantly different (P
< 0.05).
Copyright © 2013 SciRes. IJG
Multifactor-ANOVA was used to analyze the differ-
ence of filamentous cyanobacterial biomass in ponds
based upon elevation, culture system and season (Figure
6). Results show significant interaction s among elevation,
culture system and season for filamentous cyanobacteria.
Water temperature plays a significant role in the dis-
semination of phytoplankton [19]. Seasonal variability
changes algal density and diversity. The study shows that
the amount of phytoplankton in rainy season is generally
higher than in winter, except for Chlorophyta, which
conforms to the amount of chlorophyll-a in the ponds.
Furthermore, the quantity of filamentous cyanobacteria
in high input system was higher than in low input system
owing to the huge amount of nutrients present in the
former. The water temperature during the study ranged
between 28˚C - 32˚C. High fish stocking densities
(>10,000 fish ha1) and feeding rates (exceeding 70 kg
ha1·d1) resulted in high waste loading rates that often
caused excessive eutrophication in fish ponds, leading to
the proliferation of cyanobacteria [20] in high input sys-
tem, especially during the rainy season. Generally, cya-
nobacteria require higher temperature than any other al-
gae in order to increase its growth rate [21,22] hence, the
high temperature during rainy season supports highly
visible blooms of cyanobacteria, in particular, Anabaena
spp. One major implication with filamentous cyanobac-
teria , s u ch as An aba e na spp., dominating the pond waters
is the production of off-flavors, which could be acquired
by the fish and adversely affect market demand.
3.6. Managing Chlorophyll-a and Dissolved
Oxygen in Aquaculture Ponds
Chlorophyll-a and dissolved oxygen are relevant para-
meters to be managed in an aquaculture pond system.
Phytoplankton, which is indexed by chlorophyll-a, can
develop conspicuously in pond waters, leading to eu-
trophic conditions, especially during climate-driven
low-water periods. Similarly, dissolved oxygen is impor-
tant to the health of aquatic ecosystems and a key indi-
cator in determining water quality. Uncontrolled phytop-
lankton growth (high chlorophyll-a) can be a serious
problem for the farmers as it takes more oxygen out of
the water during the night than what remains in solution
from daytime photosynthesis. Moreover, phytoplankton
die offs can increase bacterial decomposition and the
reduction in normal oxygen production can lead to oxy-
gen depletions, high ammonia levels, and stressed or
dead fish. To alleviate this problem mechanical aeration
must be applied to meet the increased demand for oxygen
and prevent oxygen depletion and subsequent fish losses
or stress [22]. In high input systems nutrient reduction is
arguably the best strategy to reduce the incidence of al-
gae, especially harmful cyanobacterial blooms [23]. Thus,
maintaining the suitable amount of phytoplankton in fish
pond is important.
An important limitation of this study was the restric-
tion of sampling to just two time periods. Observations
over more months and multiple years are needed to fully
the effects of seasons and other climate-driven factor s on
chlorophyll-a and dissolve d o xygen relationships .
5. Conclusion
The relationships between chlorophyll-a, and DO max or
DO min were complex, being effected by season, nu-
trient inputs and elevation. Taken together findings sug-
gest that other factors other than algal photosynthesis
were involved. As would be expected chlorophyll-a was
much higher in high input than in low input ponds. Sig-
nificant interactions were observed for total bacteria and
filamentous cyanobacteria between elevation, culture
system and season. Divisions Chlorophyta and Cyano-
phyta had the most number of genera identified in both
seasons with Pediastrum spp., and Scendesmus spp., and
Anabaena spp. as dominant genera/genus, respectively.
6. Acknowledgements
The work was carried out with the aid of a grant from the
International Development Research Centre, Ottawa,
Canada, as a contribution to the AQUADAPT project.
Figure 6. Density of filamentous cyanobacteria in ponds at different elevation and culture system in 2 seasons.
Cells mL
Elevation, mas l
high input rainy
Filamentous Cyanobacteria
Copyright © 2013 SciRes. IJG
Special thanks to Redel Gutierrez of Maejo University
for editing this paper.
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