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: abouzied2004@yahoo.comABSTRACT:

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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