Running Title: Acclimation of red tilapia hybrid larvae to increasing salinities
Title: Performance of newly-hatched red tilapia hybrids to increasing salinity levels
Authors: Charlie H. Abayon, Arlene L. Avillanosa* and Christopher Marlowe A. Caipang
Affiliation: College of Fisheries and Aquatic Sciences, Western Philippines University,
Puerto Princesa Campus, Puerto Princesa City 5300, Palawan, Philippines
Corresponding Author: *Arlene L. Avillanosa
College of Fisheries and Aquatic Sciences, Western Philippines
University-Puerto Princesa Campus, Puerto Princesa City 5300,
Palawan, Philippines
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Abstract
The effects on survival, feeding response and growth of newly-hatched red tilapia hybrids
to gradual increasing salinity levels were assessed. Newly-hatched fry were reared in 3-L aquaria
containing either freshwater (Treatment 1) or in water subjected to weekly increments of 5 ppt to
a final salinity of 34-35 ppt (Treatment 2) for 42 days. Each treatment had 5 replicates with a
stocking density of 10 larvae per liter. Survival was relatively similar for both treatment groups.
Likewise, no significant differences (p > 0.05) were observed in the feeding response, weight
gain, specific growth rate (SGR) and feed conversion efficiency (FCE) in both treatments. Taken
together, the results showed that tolerance of red tilapia hybrids to saline waters begins early in
its life history and has a potential to be developed for culture in areas with sufficient supply of
brackishwater or with limited freshwater source. It is recommended that this laboratory-based
study on the performance of red tilapia in saline waters be tested in large-scale brackishwater
ponds or cage culture in marine areas to assess the feasibility of this fish as a candidate for
brackishwater aquaculture or mariculture.
KEY WORDS: fry, growth, hatchery, Oreochromis sp., saline-tolerant, survival
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Introduction
Tilapias are freshwater fish but can tolerate wide fluctuations in water salinity (Ernest et
al., 1991; Watanabe et al., 1992). Among freshwater fish species, tilapia has the fastest growth in
production and widespread appeal in the global market. As a result of its popularity, tilapia is
now known as the ‘aquatic chicken’ due to its robust adaptability to a wide range of
environmental conditions, ease of reproduction in captivity and has a neutral flavor of the meat
that appeals to many consumers (Little, 1998).
Tilapia is one of the best candidates for aquaculture in both brackish- and seawater
environments due to their ability to tolerate wide range of water salinity levels (El-Sayed, 2006).
It was supported by Iqbal et al. (2012) and (Pullin 1982), which reported that tilapia is one of the
important fish species that has several good qualities including good growth in water salinities
ranging 0 to 29 ppt, ability to withstand water temperatures between 8 to 42˚C, and can survive
in low dissolved oxygen (DO). While several studies in the past have demonstrated the
feasibility of culturing tilapias in saline waters, Cnaani and Hulata (2011) stressed that there are
still other approaches that can be utilized to enhance the tolerance of tilapias to saline
environment and the underlying mechanisms that are involved in their improved performance in
saline waters as well as better growth and survival. Examples of these approaches are through
selective breeding (Jaspe and Caipang, 2011a) and hybridization (Lutz, 2001).
The red tilapia hybrids, which are genetic mutants selected from crosses of two species of
the genus Oreochromis, is increasing popularity among fishfarmers and consumers because of its
attractive color, good market price and high salinity tolerance (Carberry and Hanley, 1997;
Gonzalez, 1997; Vadhel et al., 2017). The first reported red tilapia hybrid, known as the
Taiwanese red tilapia, was produced in the late 1960s and was a cross between a mutant reddish-
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orange female O. mossambicus and a normal male O. niloticus (Galman and Avtalion 1983).
Another red tilapia strain, the Florida red tilapia was developed in the 1970s by crossing a
normal colored O. hornorum female with a red-gold male O. mossambicus (Behrends et al.,
1982). A third red tilapia strain was developed in Israel by crossing a red Nile tilapia originating
from Egypt with a wild-type Blue tilapia (Hulata et al. 1995). All these hybrids have been
distributed to different tilapia-producing countries and have been found to be suitable for culture
in both brackish- and seawater (Liao and Chang, 1983; Green, 1997; Watanabe et al., 1997).
In the Philippines, several red tilapia strains are available for culture and the strain/stock
is designated based on the name of the farm/research institution where the fish were obtained
(Romana-Eguia and Eguia, 1999). Earlier studies on growth of this species in lakes and ponds
(Galman et al., 1988; Pruginin et al., 1988; Romana-Eguia and Eguia, 1999), as reference species
in evaluation trials for Nile tilapia (Basiao and Doyle, 1990; Eguia and Eguia, 1993) and
breeding performance (Galman et al., 1988; Eguia, 1996) have been conducted. However, the
performance of the red tilapia hybrids during exposure to increasing salinity levels during their
early life stages is not well-documented. The various indicators of performance of the newly-
hatched red tilapia hybrids must be elucidated so that prospective tilapia farmers will have a
reference point in assessing the likely performance of this species during the grow-out phase.
Hence, this study was conducted to determine the survival, growth and feeding activity of the
newly-hatched red tilapia hybrids during exposure to gradual increase in salinity levels.
MATERIALS AND METHODS
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Study site
The study was conducted at the Aquatic Science Laboratory (ASL) of Western
Philippines University (WPU), College of Fisheries and Aquatic Sciences (CFAS) located in
Puerto Princesa Campus, Puerto Princesa City, Palawan, Philippines.
Breeding of tilapia for fry production
Prior to the breeding activity, red tilapia spawners (180-200g) were randomly selected
from the existing broodstock tank of ASL. Female fish were separated from the males by manual
inspection of the genital papilla. Fish were conditioned for two weeks in the conditioning tanks
and were provided with adequate aeration and feeding at 3% of its biomass. Spawning activity
was done upon mixing the male and female spawners at a 1:3 male-to-female sex ratio in 6 units
of 1.0m x 1.0m x 1.0m “hapa” net that was suspended inside the circular tank. On the 4 th day of
pairing, daily monitoring of the fish was done to check for the presence of fry in the tank until
the 14th day. After two weeks, all spawners were returned to the conditioning tanks. Newly-
hatched fry were maintained in the hapa net and subsequently used for the experiment after they
have completed the yolk-sac stage.
Experimental set-up and design
Ten (10) aquaria measuring 20cm x 13cm x 20cm were randomly arranged in a
completely randomized design (CRD). There were two treatments with five replicates each.
Treatment I served as control (freshwater) while Treatment II contained water with increasing
salinity levels in multiples of 5 ppt increment per week until a final salinity of 34-35 ppt.
Adjustments in the salinity followed the protocol described by Talaver (2017) modified from
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Lemarié et al. (2004). Each aquarium has a capacity of 3 liters and was stocked with the newly-
hatched larvae at a density of 10 fry per liter.
Water and feeding management
The quality of water (pH, DO and temperature) and salinity were monitored daily. All
uneaten food and feces that accumulated at the bottom of the aquaria were siphoned and water
was added to maintain the desired water volume in each aquarium.
Commercial fry mass (CP=40%) for tilapia was given at 30% of the fish biomass.
Feeding was done four times a day based on the standard feeding protocol for tilapia fry. The
behavior of the fish was observed four times daily especially during feeding time. Uneaten feeds
were recorded to obtain data on feeding or non-feeding activity.
Zootechnical parameters
Daily monitoring was done to determine the mortality of fry from which the survival rate
was determined (Watanabe et al., 1990). Feeding efficiency (FCE) (Steffens, 1989), specific
growth rate (SGR) (Clark et al., 1990) and weight gain (Watanabe et al., 1990) were calculated
indicators of the feeding behaviour and growth performance of the fry.
Data analyses
Means and standard deviations of all the zootechnical parameters were obtained for the
two treatments. The data in the two groups were compared using Student’s t-test for independent
samples. All statistical computations were performed at the 0.05 probability level. Analyses were
performed using the statistical package of Microsoft Excel 2010.
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RESULTS AND DISCUSSION
Survival of the newly-hatched red tilapia hybrids in freshwater (Treatment 1) and
exposed to increasing levels of salinity (Treatment 2) over a 42-day observation period is shown
in Fig. 1. The mean survival of the red tilapia fry was higher in Treatment 2 (73.3%) than in
Treatment 1 (57.5), although the survival rates in both groups were comparable (p > 0.05). No
mortality in the tilapia fry was observed for 2 weeks. Mortalities were only observed beginning
14th day and lasted until the 35th day. Survival of the fry in both groups stabilized on the 35 th day
until the termination of the experiment.
In terms of feed consumption of the red tilapia fry in both groups, results showed no
significant difference (p > 0.05) in rate of the consumption of feeds during the study period (Fig.
2). This was evident in the feeding behaviour of the fish in both treatment groups. During
feeding time, the red tilapia fry actively swam towards the feed and showed continuous feeding
until satiation.
The culture performance of fry was determined based on their growth performance as
shown in Table 2. After 42 days of culture, the red tilapia fry exhibited no significant
differences (p > 0.05) in weight gain, specific growth rate (SGR) and feed conversion efficiency
(FCE) in both treatment groups.
Based on the results of the present study, the survival of red tilapia fry exposed to
increasing salinity levels were comparable with the batch that was reared completely in
freshwater conditions. The present study corroborated the results of the recent studies of El-
Sayed (2006), Jaspe and Caipang (2011b), Lawson and Anetekhai (2011) and Iqbal et al. (2012).
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According to El-Sayed (2006), tilapia is an excellent candidate for aquaculture in brackishwater
and seawater due to their ability to tolerate a wide range of salinity. Tilapias are now being
cultured in brackishwater ponds, where salinity levels could reach seawater strength during the
summer months (Jaspe and Caipang, 2011b). The ability of tilapias to withstand a wide range in
salinity levels is dependent on the ability of the body fluids to function in an abnormal range of
internal osmotic and ionic concentrations (Holliday and Jones, 1967; Lawson and Anetekhai,
2011). The fish can regulate the body fluid to restore level of osmotic pressure to near normal
when exposed to increasing salinity levels and this ability is demonstrated early in the life stages
of red tilapias, as what has been observed in an earlier study by Nugon (2003). The weekly
increment of 5 ppt was the appropriate regime in acclimating red tilapia fry to increasing salinity
levels as fish mortality was not drastic. This regime was within the concentration of daily salinity
increments recommended by Lemarié et al. (2004) during acclimation of tilapia juveniles higher
salinity levels.
Red tilapia, particularly the Florida red tilapia strain, are able to reproduce in salinities up
to 36 ppt, however, egg fertilization, hatching, and survival of larvae is highest at 12 g/l and
drops markedly after 18 g/l (Watanabe et al. 1997). Hence, it was not surprising that there was a
considerable drop in survival of the newly-hatched red tilapia larvae when the salinity was 20
ppt, which was on the 28th day of rearing. However, in freshwater conditions, the same pattern of
mortality was also observed. Although, survival rates of the red tilapia fry was comparable in
both freshwater and saline environments, the survival of the fry in increasing salinity was a little
bit higher than those reared in pure freshwater. Watanabe et al. (1997) and Liao and Chang
(1983) also observed equal to or better growth of red tilapias in seawater than in freshwater.
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The restlessness or erratic swimming behaviour of fish that are exposed to high salinities
indicates a fast rate at which the fish are approaching their tolerance limits to salinity (Lawson
and Anetekhai (2011). According to Xu et al. (2005), the feeding behavior of tilapia is altered or
they stay at the bottom of the tank when they are stressed due to their exposure to a wide salinity
gradient. In this study, the red tilapia hybrid fry did not exhibit sluggish or erratic swimming
patterns during gradual changes in the salinity of the rearing water, indicating tolerance to
salinity increments in the aquaria. Moreover, a good feeding behavior displayed by the fish
towards food during feeding time as shown by the high rate of feed consumption is an indication
that the metabolism of the fish was not impaired as a result of these gradual changes in salinity
levels (Lawson and Anetekhai, 2011).
Because of the comparable performance of newly-hatched red tilapia in terms of survival
and growth in both freshwater and in increasing salinity levels, the culture of this fish may be
viewed as a practical alternative to shrimp or milkfish farming particularly in areas where there
are limited sources of freshwater. Further studies are needed to validate the performance of this
hybrid during large-scale operations in ponds or cages in fresh- , brackish- or seawater in order
to confirm these results in the short-term study.
CONCLUSION
In conclusion, this study has shown that the tolerance of red tilapia hybrids to saline
waters begins early in its life history. Survival, growth and feeding activity of the newly-hatched
red tilapia hybrids were comparable in both freshwater and saline water, which may have
implications on their performance during the grow-out phase.
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ACKNOWLEDGEMENTS
This study was partly funded by the CHED-NAFES Extension Project, “Western
Philippines University Learning Environment-friendly Advocacy Farm and Family-based
Education Towards Fisheries Resource Management and Popularization of Aquaculture and
Alternative Agriculture in Western Philippines”. CMA Caipang is supported by the Balik
Scientist Program of the Department of Science and Technology, Philippines. The project staff
of the CHED-NAFES project and some personnel of the College of Fisheries and Aquatic
Sciences of WPU assisted in the conduct of this experiment. Dr. Roger Dolorosa and Dr.
Herminie Palla have significant contributions to improve the manuscript.
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FIGURE LEGENDS
Figure 1. Survival of the newly-hatched red tilapia hybrids reared in freshwater (Trt 1) and in
gradual increase in salinity (Trt 2) over a period of 42 days. Red tilapia fry reared in Trt 2
were exposed to weekly increments of 5 ppt in water salinity. N=5.
Figure 2. Feed consumption rate (%) of the newly-hatched red tilapia hybrids reared in
freshwater (Trt 1) and in gradual increase in salinity (Trt 2) over a period of 42 days.
N=5.
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