INFLUENCE OF LOW SALINITY ON SURVIVAL AND GROWTH OF
THE EGYPTIAN SOLE Solea aegyptiaca
Ramadan M. Abou ZiedFaculty of Agriculture- Fayoum University- Egypt. POBox: 63514E-mail: [email protected]:
This study was conducted to evaluate the effect of low salinity on survival
and growth of the Egyptian sole Solea aegyptiaca through two stages. The first
stage is acclimatization and rearing Egyptian sole fish at different salinities, 5, 10,
15, 20 and 25 ppt for 25 days. Fish with an average weight of 24.2 ±1.86 g were
randomly stocked at a rate of 10 fish/glass aquarium (100 L). The second stage is
growing sole fish in low water salinity of 6.0, 0.85 and 5.2 ppt in a commercial fish
farm. All the treatments were conducted in duplicate. Survival rate (SR), total
weight (TW), specific growth rate (SGR) and growth rate were evaluated. At the
first stage, significant (P≤0.05) differences in SR% was recorded and the highest
was at 5 ppt salinity and lowest recorded at 25 ppt salinity. In the second stage,
significant (P≤0.05) differences were observed in all growth parameters except
final weight and the highest values with 31 ppt than 5 ppt. But
Hepatosomatic Index (HSI) and condition factors (CF) significantly increased
values under low salinity than that cultured in water of lake Qarun 31ppt and wild
fish catched from lake Qarun which in the same level. The present study
recommended that, Egyptian sole can be cultured in brackish water with high
survival and acceptable growth rate.
Keywords: Egyptian sole, Salinity, Survival, Growth, Condition factor and
Hepatosomatic index.
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1.INTRODUCTION:
Fish culture sector has been expanded extensively in the last decades, but
this growth can mainly be attributed to the culture of new marine species which
already shows increasing in the market demand. Scientific and technical interests
have been focused on high value native marine species, whose biological cycle
can be reproduced using currently available breeding techniques such as sole,
Solea solea, (Yones and Abdel-Hakim, 2011).
Because of the shortage of fresh water sources, many fish farmers are
looking for marine aquaculture. Egyptian sole is one of the native fish in Lake
Qarun. The total Egyptian production of sole was 2115 ton constituting 0.15% of
total fish production (GAFRD, 2012). Lake Qarun production of fishes was 4410
tons while the production of sole was 946 tons (21.45%).
Salinity is one of the most important abiotic factors, which affect the
growth, body composition, and energy budget of aquatic organisms by exerting
complex and wide-ranging biological effects (Brett and Groves, 1979; Gaumet et
al., 1995; Kumlu et al., 2000; Boeuf and Payan, 2001 and Mookkan et al. 2014 ).
There are important commercial interests in determining the optimum salinity for
each commercial fish species in intensive systems where the salinity can be
altered to fit the species. A number of studies have been focused on the effect of
constant salinity on aquatic organisms. It is generally accepted and preferred that
aquatic organisms grow better at constant salinity rather than fluctuating salinity.
However, the positive influence of fluctuating salinity on the growth of aquatic
organisms has previously been reported (Stroganov, 1962; Konstantinov and
Martynova, 1993). Production of sole under moderate salinity fluctuations was
reported by Khairnar et al., 2015 and found that commercial farmers are
recommended to rear juvenile tongue sole with moderate salinity fluctuations for
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better growth performance of this species. Effects of salinity on osmoregulatory
processes and their impact on growth have been studied in estuarine species such
as the milkfish Chanos chanos fry (Alava, 1998) and striped bass Morone saxatilis
larvae (Peterson et al., 1996) and they have stated that the younger fishes prefer
the environments of lower salinity levels.
The soles (Soleidae) are very important species in the Egyptian
Mediterranean fisheries, where Egyptian sole (Solea aegyptiaca) is the most
common species. Soles contributed with about 6.5% of the total catch of trawl
fishery, forming about 13% of the gross revenue of the trawling. There are
discrepancies regarding the taxonomy of the species S. aegyptiaca, because the
examination of its morphometric characters shows that it cannot be separated
from Solea solea (Ben-Tuvia, 1990). S. aegyptiaca is considered a valid species in
some studies (Bauchot, 1987; Goucha et al., 1987; She et al., 1987). In some
studies it is considered a synonym of Solea solea (Borsa and Quignard, 2001),
while in some others it is synonymized under S. vulgaris (Tinti and Piccinetti,
2000). Despite the great importance of soleid species to the economy of the
Egyptian fisheries, they have been sparsely studied. El- Gharabawy (1977) studied
the taxonomy of soles in Egyptian Mediterranean waters. Kerolus (1977) studied
the meristic characters and used the vertebrae in age determination of Solea
vulgaris in Lake Qarun. Ezzat et al. (1982) studied the age and growth of Solea
vulgaris and S. aegyptiaca in Abu-Qir Bay.
El-Far (2014) reported that sole fishes in lake Qarun were represented
mainly by S. aegyptiaca (dominant) and S. solea. Age, growth, reproduction, food,
feeding habit and population dynamic of S. aegyptiaca were determined. It was
found that S. aegyptiaca had allometric growth with maximum age of 4 years,
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spawn during winter with average length at first sexual maturity of 15.7 cm, and
feed mainly on rotifers, copepod, annelids and crustaceans.
The present study was carried out to investigate the best water salinity for
rearing S. aegyptiaca and the possibility of S. aegyptiaca to be cultured in brackish
water (low salinity) in commercial farms.
2. MATERIALS AND METHODS
2.1. Fish and experimental design
The present experiment was carried out at Demo experimental station,
Faculty of Agriculture, Fayoum University, Egypt, started in 28 December, 2014
and continued for 86 days (41 days acclimation period + 45 days growth period)
through two stages. The first stage is acclimatization and rearing Egyptian sole fish
at different salinities, 5, 10, 15, 20 and 25 ppt for 25 days. Fish cached from a wild
Lake Qarun with an average weight of 24.2 ±1.86 g were randomly stocked at a
rate of 10 fish/glass aquarium (100 L). Fish were acclimatized to laboratory
condition for a week prior to experiment. Then they were acclimated to five
different salinities (5, 10, 15, 20 and 25 ppt) by gradually decreasing water salinity
by 5 ppt, per 3 days until reaching the tested salinities. Each aquarium was
supported with 5 cm sand. Water salinity of all aquaria softened until salinity of
25 ppt gradually using fresh water for 3 hours using a narrow hose. After 3 days
were left two
aquaria on the salinity (25ppt) and dilute another aquaria salinity gradually
to 20 ppt by previous method left for 3 days. This method repeated until reached
to salinity 5 ppt (Table 1).
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Table (1). Plan of the experiment.
Period adjusted salinity levelAquarium NoSalinity levels
13/1/201510/1/20157/1/20154/1/20151/1/2015
25 ppt25 ppt25 ppt25 ppt25 ppt1 and 22520 ppt20 ppt20 ppt20 ppt25 ppt3 and 42015 ppt15 ppt15 ppt20 ppt25 ppt5 and 61510 ppt10 ppt15 ppt20 ppt25 ppt7 and 8105 ppt10 ppt15 ppt20 ppt25 ppt9 and 105
Fish were fed with small shrimp to satiation. Fish aquarium was supported
with one air stone. Twenty percent of water in each aquarium was changed every
day. The experiment lasted for 25 days after the arrival to the lowest salinity of 5
ppt. 100 fish was put in a m3 tank with a water salinity of 5 ppt had a aerators as
an extension of fifth treatment backed up to used. Second stage (growth), fish at
low salinity (5 ppt) from aquarium and extension tank was transferred to three
commercial farms.
1. Fish stocked at 10 pcs/ hapa, (5 × 7m) in a commercial farm in Shakshuk
Area under water salinity of about 6.2 ppt, with two replicates.
2. Fish stocked at 10 pcs/ hapa, (5 × 7m) in the farm of Faculty Experiment
Station under water salinity of 0.85 ppt, with two replicates.
3. Fish stocked at 10 pcs/ fiber tank (1 m3), with two replicates at National
Institute of Oceanography and fisheries near Lake Qarun. Tanks were filled
with brackish water at salinity of 5 ppt with aeration. Fish was fed with
small shrimp to satiation for 45 days.
At the end of the experiment, growth parameters and survival rate were
measured as follows:
- Weight gain = Final weight - Initial weight
- Daily gain = Weight gain, g /period in days.
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- Specific growth rate (SGR,%) = 100 (ln Final weight-ln Initial weight)/period in
days, where ln is the natural log.
- Survival rate (SR) %= Final number of fish /Initial number of fish x 100.
- Relative intestine length (RIL) = intestine length (mm) / body mass (g)
- Hepatosomatic index (HSI) = 100 x liver mass (g) / body mass (g)
- Condition factor (CF) =100 x W/L³ where W= Weight (g), L = Total length (cm).
2.2. Water quality measurement
Water temperature, pH, dissolved oxygen (DO2), ammonia (NH3-N) and salinity
throughout the experimental period were measured periodically in the morning
and at noon by Orion digital pH meter model 201, oxygen meter, Cole Parmer
model 5946, HACH test kit ammonia mid-range 0-3 mg/L model NI-8 and TDS
apparatus, respectively.
2.3. Statistical Analysis
Statistical analyses were performed using SPSS version 16.0 (2007). One way
analyses of variance was used and significance among treatments was evaluated
at the 5 % probability level according to Duncan (1955).
4. RESULTS AND DISCUSSIONS:
4.1. Water quality:
Water quality parameters were shown in Table 3. The values of parameters
such as temperature, dissolved oxygen, pH, ammonia and unionized ammonia were
within the optimum ranges for rearing sole according to Fonds (1976), Alderson
(1979), Parra and Yúfera (2002) and Imsland (2003). But the values of unionized
ammonia in pond contains water salinity of 25 ppt was higher and harmful for
intensive culture thus decreased the survival rate.
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Table (2). Average value of Water quality parameters during the experimental period in aquarium
un-ionized ammonia*NH3-HpH
Dissolved oxygenMg/L
TemperatureoCSalinity levels (ppt)
0.0872.08.297.919250.0482.08.177.819200.0502.08.147.819150.0512.07.987.719100.0532.07.767.8195
*Calculated according to Florida Department of Environmental Protection (2001).
4.2. Survival rate%:
The effect of different salinities on the survival rate was shown in Table 3. The
results showed significant differences between levels and high survival rate was
obtained with fish cultured under low salinity (5 ppt) than other salinity levels which
recorded values of (100, 95, 90, 80 and 75%) for salinities 5, 10, 15, 20 and 25 ppt
respectively. The decreased of survival rate in treatment 1 (25 ppt) may be due to
increased unionized ammonia percent than the optimal range.
Table (3). Effect of salinity levels on survival rate in glass aquaria.
Salinity ppt 25 20 15 10 5 SED
% 75c 85bc 90ab 95ab 100a 5.48
* Average in the same column having different superscripts significantly different at (P£0.05).** SED, standard error of a difference between 2 means= √(2×Error MS/r)
Results in Table 4 showed that the ability of Egyptian sole to live in a
commercial farm around Lake Qarun, where showed the high survival rate to 100%.
In the pond of National Institute of Oceanography and fisheries, survival rate was
100%, followed by 75% for hapas in the farm around Lake Qarun, but this percent
dropped to 40% in Faculty of Agriculture farm due to the low salinity to 0.85 ppt in it
because the water source of Nile river, and these results are promising for the
possibility of production Egyptian sole in the farms scattered around the Lake Qarun,
which salinity in most of them don’t less than 5 ppt. Decreased survival rate in this
farm to 75% may be attributed to the soil of the bottom of these farms (clay) fish
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cannot hide itself well and was buried as they were in ponds of National Institute of
Oceanography and fisheries with a sandy bottom.Table (4). Average value of Water quality and survival rate during the experimental period in
hapaSurvival rate%NH3-H
SalinitypptpH
Dissolved oxygenMg/L
Temperature
oCPond
750.46.28.136.722Commercial farm (hapa)400.00.857.766.821Faculty farm (hapa)
1002.05.08.277.220Institute pond
4.3. Growth performance:Results of growth performance in Table 5 showed that possibility of culture
Egyptian sole in low salinity water for 45 days with increased of growth which do not
like cultured in water of lake Qarun. Results showed that insignificant (P > 0.05)
differences in final weight but significant (P≤ 0.05) differences in weight gain, daily
gain and SGR to fish cultured in pond of lake Qarun water. But Egyptian sole
cultured in low salinity water (5ppt) don’t less much and in the same range this
indicated that possibility of cultured Egyptian sole in low salinity water. These
results was similar to weight gain, specific growth rate and condition factor were
recorded in the same species by Yones and Abel-Hakim (2011), Bonaldo et al. (2006),
Rudea-Jasso et al. (2004) and Silva et al. (2010) when cultured this species and note
that sole fish growth rate is different from other fish deployed in Egypt, such as
tilapia. The HIS is often used as an indicators of condition and nutritional status of
fish.
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Table (5). Average value of growth parameters during the experimental period (45 days) in ponds of National Institute of Oceanography and fisheries
SEDPond 31 pptPond 5 pptItem2.8223.6024.80Initial weight, g2.1629.5027.35Final weight, g1.205.90a2.55bWeight gain, g
0.0320.13a0.06bdaily gain, g0.1220.51a0.22bSGR %
* Average in the same row having different superscripts significantly different at (P£0.05).** SED, standard error of a difference between 2 means= √(2×Error MS/r)
Table 6. showed significant differences in hepato-somatic index (HIS) and
condition factors (CF), which increased values under low salinity than that cultured
in water of lake Qarun 31ppt and wild fish catch from lake Qarun which in the same
level. The values of CF was 0.66, 0.55 and 0.52 for fish under 5ppt, 31ppt in ponds
and wild fish respectively. HIS takes the same trends which values was 2.16, 0.58
and 0.55. These parameters can provide information on the general health status of
fish (Van der Oost et al. 2003). Fish cultured at 5 ppt showed an increase in CF in
comparison with fish cultured in pond 31 ppt and wild fish from lake Qarun which
could be interpreted as reflecting the availability of food reserves (increased weight
v.s decreased length) or pollution stress (decreased an unionized ammonia)
resulting in CF increase (Chellappa et al. 1995). Decreased HIS in wild fish and 31 ppt
fish may be due to high pollution of water lake Qarun and increased unionized
ammonia in pond of 31 ppt.
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Table (6). Average value of parameters during the experimental period in institute ponds
Relative Intestine length (RIL)
Condition factor(CF)
Hepatosomatic
Index (HIS)Pond
8.940.52b0.54b31 ppt7.770.66a2.16a5 ppt8.690.55ab0.58bQarun lake
Conclusion:From the obtained results, Egyptian sole can be cultured successfully under
low salinity water and the growth performance decreased than that cultured
under salt water, this indicated to culturing in commercial farms around the lake
Qarun.
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