Growth response and estimating heritability of synthetic base population (F0) of red tilapia (Oreochromis spp.) through family selection

Red tilapia (Oreochromis spp.) is widely cultivated because it has high economic value. However, at the same age, the growth and thickness of red tilapia flesh are lower than that of black tilapia, which is necessary to improve genetics, one of which is a breeding program. The purpose of this study was to evaluate growth performance and estimate the value of the genetic parameter of the synthetic based population (F0) of red tilapia. Spawning was done naturally using happa with 30 males and 90 females. The number of families produced was 30 families, consisting of male and female sub populations. Enlargement activities were carried out for 90 days with a stocking density of 7 fish/m2 and a frequency of feeding 2 times a day. The estimated heritability was 0.26±0.07 with a response to selection of 18.52 g (male) and 0.35±0.09 with a response to selection of 20.69 g (female). Based on these parameters, the selection process for the next generation can still be done by increasing the number of families.


Introduction
Red tilapia (Oreochromis spp.) is one of the tilapia strains that have high economic value in addition to black tilapia.Based on the information developed in the community, it is known that the growth performance of the fish has begun to decline.On the one hand, the demand for red tilapia for aquaculture continues to increase.The increase in red tilapia cultivation has been driven by the emergence of more attractive red snapper-like red tilapia, especially in Asian and American markets [1].However, red tilapia found in the community have a lower average weight than black tilapia at the same age.Morphologically, red tilapia grows longer but has thinner flesh than black tilapia.One of the efforts that 2 can be made for genetic improvement is through selective breeding.The advantage of selective breeding is the continuous genetic improvement achieved and passed on to the next generation to increase the productivity and profitability of aquaculture production [2,3].
According to [4] In reproductive activity, parental traits are directly passed on to offspring along with their genetic variation.Fish breeding program through selection is expected to improve genetic quality (genetic gain) better and the increase depends on the proportion of genetic diversity to the phenotypic variety inherited by the parents.The value of the proportion of inheritance numbers also called heritability) can be precisely known through selection activities from generation to generation on an ongoing basis [5,6].The selection program can be started by calculating the estimated breeding value (EBV) and determining the estimated response to selection and inbreeding rate in the population to be obtained [4,7].
So far, the selection program for tilapia has been reported mostly on black tilapia strains, namely the success of producing superior varieties that are widely cultivated in the Asian region, namely GIFT tilapia.GIFT tilapia is known to have high growth and yields [9,10].However, information on selective breeding activities in red tilapia has not been widely reported.Breeding activities for red tilapia through family selection are part of efforts to increase the performance and production of tilapia aquaculture in Indonesia.In addition, it is also expected that red tilapia grows fast and has thick flesh.In the selection program, genetic parameters such as heritability values and response to selections need to be known because they are indicators of increasing a character to predict the progress of a selection.In several species of fish reared in brackish water it is known to show a genetic enhancement value of 5 -20% [2].The purpose of this study was to evaluate the growth character improvement and estimate of heritability and response to selection of red tilapia (F0) through family selection.This is done to find out the description of the performance improvement in the next generation.

Materials and methods
The experiments were conducted in accordance with the guidelines for the care and use of animals for scientific purposes, and this study did not require research ethics approval according to the letter of notification from the secretariat of research ethic committee, National Research and Innovation Agency.
Breeding activities on red tilapia (F0) were conducted using the family selection method.This activity was divided into four spawning cohorts (groups) according to the total number of broodstock used, consisting of 120 males and 360 females (4 cohorts).The test fish used to form the F0 population were red tilapia parent resulting from a combination cross of 5 red tilapia strains namely Janti tilapia from PBIAT Janti Central Java, Sa red tilapia from Yogyakarta, Singapore tilapia from Klaten Central Java, Prima tilapia from Kalijati, West Java and NIFI F2 red tilapia bred at BRPI.This research was conducted at Research Institute for Fish Breeding, Subang, West Java for 6 months.

Spawning
Spawning activities were carried out in net sized 2x1x 1 m 3 which is placed in a 200 m 2 freshwater pond (ratio of male and female 1:3).After spawning took place for 7 days, egg collection was carried out.The total number of female broodstock that spawned was 100 so that 100 families were obtained (4 batches), but in this study only 30 families were reported (batch 1).Eggs collected from each spawning female were kept in an incubation tank for 5 days.Larvae rearing was carried out at a stocking density of 75 fish/m 2 for 60 days.Feeding (40% protein) was carried out at 08.00, 12.00 and 16.00 WIB ad libitum.after the nursery phase is complete, 50 fish were taken from each family at random, consisting of 25 males and 25 females for measurement of length, weight, and width.Then the dorsal part was tagged using the PIT (passive integrated transponder) tag.

Grow out
Juvenile red tilapia that has been tagged were then growing out communally in a 200 m 2 earthen pond with a water depth of 80-100 cm for the enlargement stage for 90 days.Juvenile were fed (30-32% protein content) every day at 08.00 and 16.00 WIB as much as 5-10% of the biomass.

Selection
Selection is done when the average weight of the red tilapia population reaches the consumption size, which is between 200-250 g/fish.The selection activity was carried out by weighing the individual weights of males and females in each family referring to [11].The lowest weight of the selected population is determined based on the results of sampling before the selection is made.The lowest weight in the best 10% of the sample population is determined as the lowest weight for the selected population (selection cut-off).Individuals selected based on the selection cut-off determination are maintained as parent candidates and used as material for the next stage of activities.In addition to selecting the selected population, a population with an average weight was also selected as an internal control population, which was done to determine the success of the selection through the response to selection test.

Parameter
The growth parameters observed included: weight gain, growth rate, thickness and survival, where growth sampling activities were carried out once a month with the number of samples observed of 10% of the number of fish.The parameters of selection activities include coefficient of variation, selection differential, estimation of heritability value, and response to selection.Here are some of the formulas used: a. Specific growth rate (SGR), based on formula [12] SGR = (ln −ln 0)  100 b.Coefficient of variation based on formula [13] CV =   100 c.The selection differential is the difference of the base population mean (x) and the mean of the selected population (x'), based of formula S = x'-x [13] d. Heritability estimate / broad sense heritability (h 2 ) based on formula [14] e. Estimation of response to selection (R).
The value of the response to selection was estimated using the Falconer formula [15].Standard error (SE) for heritability (h 2 ±SE) was analyzed by [16].

Data analysis
The data obtained were analyzed using the Analysis of variance (ANOVA) method using the SPSS.22 program, from this analysis obtained genotype variance, phenotype variance and interclass correlation to estimate heritability values and response to selection.

Results and Discussion
The growth of red tilapia in this study showed a relatively normal growth pattern for fish development (Figure 1).Since day 30, the increase in the average length and weight has begun to be seen, as well as the following month, which has experienced a relatively rapid increase.At this stage, growth is already at an accelerated stage.At the end of growth maintenance, both populations reach consumption sizes with a length ranging from 21-23 cm and a weight of 190-230 g.The pattern of increase in length and average weight of male individuals was seen to be higher than that of females, this was because in male fish the energy obtained from feed was used for growth, while in female fish there was a distribution of feed metabolism for growth and gonadal development.According to [17], internal factors that influence growth include gender and heredity, where these two factors can be controlled, one of which is the selection method to find the highest fish growth among individuals and between families.[15] stated that environmental factors will affect the phenotypic appearance of an individual and the fish population that we maintain, although genetic variation and environmental variation together form phenotypic variations that cause individual appearance differences, where the appearance of male fish is influenced by sexual dimorphism who have a larger body size even though they are the same age [18].Based on the results of statistical tests showed that the growth of red tilapia was significantly different (P <0.05) with the highest growth value in male tilapia which achieved a weight gain of 220.91 g, SGR 3.40 % weight/day and DGR 2.45 g/day (Table 1) The high value of weight growth in male red tilapia of the base population was in line with the high values of body thickness, biomass and survival of 21.33 mm, 17.0296 g, 85.33%, respectively.Statistically, this value showed a significant difference (P<0.05).These results are following the report of [19,20] in cultivation it is known that male fish have faster growth than females.This is because, in addition to protein feed used for egg production, female fish when incubating eggs, tend not to eat, so growth is stunted.[21] stated that in tilapia, female fish grow faster than male fish when kept separately.According to [22] Growth of red tilapia reared for 130 days showed a weight of 247.2 ± 3.09 g (male) and 209.9 ± 3.38 g (female).Then [23] reported that the survival value of monosex tilapia (77%-81%) was higher than that of mixed sex fish (55%-65%) during the 140-day rearing period.
In general, the selection will be made based on the superiority of the growth rate character, i.e., only fish with a high growth rate (indicated by the high individual weight in each family) at the end of the rearing phase, are used as the parent to form the next generation population.This growth advantage is expected to be inherited and can be increased in the next generation through a selection program The basic population (F0) of male and female red tilapia showed moderate values of the coefficient of variation (CV) namely 21.54% and 21.25%, while the thick characters were low at 8.31% (males) and 8.84% (females) (Table 2).The relatively moderate CV value on the weight character indicates that there are phenotypic variations in the red tilapia population which gives great hope for the success of the selection because it is formed from various strains of red tilapia, this is related because the value of phenotypic variation is positively correlated with genotype variations.According to [24,25] the sustainability of a species or population to adapt to environmental changes in the long term depends on genetic diversity.[26] states that the coefficient of weight diversity in fish ranges from 17-29%.These results are consistent with the report of [27] that black tilapia kept in ponds showed CV values ranging 12-31% (males) and 9-24% (females).However, this value is lower than [28] that the CV value of tilapia from Generation 1 to Generation 4 ranges 27-38% with an estimate that there will be an increase in CV value in 14 th generation tilapia which is 92.29%.Then the report of [23] on monosex and mixed sex tilapia ranged 26-34%.As for other fish species such as carp (Cyprinus carpio), it shows a CV value of 25.24% [29] and carp punten strains of 27.92% (F0) and 37.15% (F1) [30].According to [31] the coefficient of variation provides an overview of the phenotypic diversity that will support the success of a selection program where a population with a high coefficient of variation will have a more successful chance in the selection program because it is more diverse.The factors that cause low diversity values include nutritional deficiencies, disease and poor management of cultivation and offspring [15,32].Meanwhile, [33] states that the low value of the coefficient of variation can be assumed to have good social interaction and the absence of competition.Based on the data on the average weight of the basic population of red tilapia from each family, a cut-off (5-10%) was carried out to select individuals within the family (within family).The weight cutoff value for male tilapia is 280 g, this value is 27% higher than the female fish, while the thick characters look the same, namely 35.00 mm (males) and 34.00 mm (females) (Table 2).The average value of the weight selection differential reached 72.15 g (male) and 59.18 g (female), while the thick characters were 3.44 mm (male) and 4.68 mm (female).This selection difference value indicates that the higher the potential for genetic improvement, the higher the yield, which influences the growth response of the next generation of red tilapia.According to [34] The selection response that will appear in the next generation shows the magnitude of the differential selection value that is inherited.Even though [35] stated that if only a small number of selected individuals were obtained, a high selection differential could not be used as a reference for calculations, because it could trigger an increase in inbreeding rates.The rate of intergenerational inbreeding occurs when a limited number of parents are used for spawning, besides this will cause a decrease in the fitness of a character in the fish population [26].In this research, the heritability value obtained is the estimated value.Although estimation, this value can be used to measure the ability of a genotype consisting of additive and non-additive diversity elements in the population to inherit traits.[36] stated that increasing genetic quality in the next generation can use the results of heritability calculations in a broad sense as the basis for the initial estimation of response to selection calculations.The heritability of a character is an illustration of how high (variance) genotype affects phenotypic diversity [24].The heritability value estimation of female red tilapia is known to show a higher value than male fish, which are 0.35±0.09and 0.26±0.07,respectively (Table 3).According to [11], heritability ranging from 0.2 to 0.4 is in the medium category, while the low category is category is low (<0.2), and high (>0.4).[28] reported the weight of black tilapia showed moderate category heritability values of 0.251 (males) and 0.258 (females).This value is consistent with based on several studies reporting that the estimated heritability value of weight character in tilapia is included in the moderate category including blue tilapia of 0.38 ([4] monosex tilapia of 0.21 [23] and red tilapia was 0.38 [22], but higher results were reported by [37] that heritability estimates for tilapia reared in ponds, floating nets and rivers were 0.55, 0.52, and 0.49 respectively.The estimated heritability value for red tilapia kept in ponds is known to be 0.49 (male) and (0.19) female respectively [38] and 0.42 black tilapia [29].Based on the estimated heritability value, it can be assumed that the red tilapia selection activity can be continued.[40] states that if a high heritability estimation is obtained, then the selection can be made in the early generations because the character of a genotype is easily passed on to their offspring.The high and low heritability values are influenced by the type, age of fish, research methods and environmental conditions which the research is carried out.This value is also very specific to the fish population and applies at certain times, locations, and environmental conditions [36].Likewise, the estimated heritability values for weight and body height of tilapia reared in ponds with aeration were (0.23 and 0.18) and in ponds without aeration (0.21 and 0.20) [41].
In this study, estimation of selection response was also performed on the base population of red tilapia.This response to selection value is a description of the genetic progress that will occur in the next generation based on the selected character (weight), where if the expected genetic progress value is high then the selection activity is said to be successful.In line with the heritability value, the estimated response to selection value in this study showed that female red tilapia (18.52 g or 7.99%) had a higher response to selection than male tilapia (20.60 g or 10.71%).According to [42,28] stated that the magnitude of the genetic gain value as an effect of selection is influenced by the value of the coefficient of variation and the intensity of selection, where a higher response to selection is also associated with a high intensity of selection in male and female elders used compared to the previous generation.If the weight distribution pattern is skewed to the right, the individuals with weights above the average population weight will be fewer and the value of the selection difference is relatively smaller.[43] stated more accurate estimation of genetic correlation and with small error requires a large sample size because it correlates with environmental and genetic variation additives.As [41] stated that constructing parental genotypic pedigrees, deleting small families, using SNP array data, and increasing the number of experimental fish can be used to determine genetic correlation estimates.The value in the study is not much different from the report [44] in that the average estimated genetic gain for body weight is 12.7%.Several studies on tilapia reported that the average boot response to selection ranged from 10-15% per generation [45][46][47].Meanwhile, [46] and [48] reported a low weight response to selection in tilapia of 3.8%-5.4%per generation.According to [49] evaluation of the growth and performance of tilapia aquaculture is needed to measure the diversity and genetic purity of the brood stock used.The growth performance of tilapia can be improved by selecting fish from crosses or by selective breeding, where the maternal component is an important thing that can affect body characteristics [50].Then [51] reported that the advantage of a selective breeding program in brackish water is that it eliminates the cost of transporting selected candidate fish and reduces the possibility of disease transfer.In addition, it was also reported that selection on the character of weight can increase the thickness of tilapia skin [52].

Conclusion
The basic population growth of male red tilapia showed higher than female tilapia.The estimated heritability value of the basic population of red tilapia was in the medium category, namely 0.25 (male) and 0.35 (female) with the expectation of a response to selection of 7.79% (male) and 10.71% (female).The heritability estimate value that is moderate on the weight character, indicates that the selection activity can be continued in the next generation.

Figure 1 .
Figure 1.Growth pattern of base population of red tilapia for 90 days' period

Table 1 .
Average base population growth of red tilapia.
*The same letters in the same row indicate that no significant differences were found

Table 2 .
Coefficient of variance, cut off, selected weight, selected thick and Selection Differential of base population (male and female) of red tilapia.

Table 3 .
Genetic parameters of base population (male and female) of red tilapia.