Heterosis and maternal effect on parameters related to productivity of 25 cross populations between five strains of common carp

. Heterosis is a comparison of the performance of hybrid fish compared to their parents. Positive heterosis indicates the hybrid performance is better than the parents' average. The maternal-effect in the hybridization process causes the heterosis not to be the only consideration in the formation of hybrid fish. The primary goal of this study was to estimate heterosis and conduct an evaluation of the maternal effect, especially on parameters related to the productivity of cross-population between five common carp strains in Indonesia, specifically Majalaya (MJ), Rajadanu (Rj), Sutisna (St), Wildan (Wd), and Sinyonya (Sy). The grow out of the hybrid and inbred line populations was carried out in 25 net cages, measuring 5x5 meters, for 90 days. The fish rearing was conducted with three replications. The results showed that the highest heterosis for harvested biomass as the productivity parameter was achieved in the five crosses, that is, Rj >< St, Rj >< Mj, Mj >< St, Sy >< Stand Sy >< Mj. The common carp strain with the highest maternal effect on the productivity parameter is the Majalaya strain. Female selection in the Majalaya strain affects the performance in terms of phenotypic characteristic of the cultured hybrid common carp


Introduction
Farmers in Indonesia have observed a decrease in the growth rate of common carp for more than the last decade.The decrease in the growth rate of carp is thought to be caused by the high rate of inbreeding in the seed population.Allegations of high levels of inbreeding are based on the reality in the field, namely the limited number of broodstock in most carp hatcheries [1].In addition to the limited number of broodstock, the exchange or distribution of broodstock between hatcheries also occurs with high intensity.[2] reported that the inbreeding rate of cultured common carp in Indonesia has reached a very high, ranging from 0.787 to 0.916.
Efforts to improve the quality of carp seeds, primarily through efforts to reduce the level of inbreeding, have been made little.One of the relatively fast breeding methods to reduce inbreeding rates is through a hybridization program.In addition to improving its genetic quality, the hybridization program also aims to obtain hybrid seeds as candidates for superior varieties.Performance evaluation of hybridized seeds was carried out through heterosis analysis (hybrid vigor), namely comparing the performance of hybrid seeds with their parents [3][4][5][6][7][8][9][10]. Heterosis estimation has been carried out on several types of freshwater hybrid fish, including African catfish [11,12], tilapia [13,14], gourami [15,16], Siamese catfish [17,18], and others.
The success of the hybridization program is influenced by genetic characteristics such as genetic distance, genetic variance, combining ability, and gene action in crossing two different populations [19,20,21,22].Besides being influenced by genetics, the maternal effect and reproductive behavior on fish hybridization activities also affect the performance of the hybrid population produced [4].The maternal effect on crosses between populations or strains of common carp in Indonesia has yet to be studied more.The objective of this study was to estimate the heterosis and conduct an evaluation of the maternal effect on three main culture characters related to productivity: specific growth rate, survival rate, and harvested biomass of the hybrid fish resulting from the crosses of five common carp strains.

Material
The main focus of this research involved utilizing five high quality common carp strains obtained from the Research Institute for Fish Breeding (RIFB) in Sukamandi.This five strains were specifically Rajadanu (Kuningan, West Java), Majalaya (Bandung, West Java), Sutisna (Kuningan, West Java), Wildan (Cianjur, West Java), and Sinyonya (Pandeglang, Banten).Subsequently, these five common carp strains were then crossed to form 25 fish populations consisting of five true-breed populations, 20 hybrid populations, and 20 reciprocally hybrid populations.The fish test was obtained from nursery stage 2 (P2), weighing 10-12 g/individual.The number of fish for testing is as many as 450 individuals per cross-population.

Crossing method
The complete diallel cross method was employed for the accomplishment of crossbreeding, which involved crossing each strain with all the other strains, resulting in a total of 25 cross combinations.The crossbreeding design of the five common carp strains is detailed in Figure 1.For each strain, three males and three females were paired for the crossing.
The spawning was carried out using the artificial spawning method following [23].Fish rearing of 25 populations resulting from the crosses was carried out using a 3x5x1 meter net cage which was positioned in an earthen pond with a water depth ranging from 0,8 to 1,5 meters.The experimental design used is a completely randomized design with three replications.There were 150 fish placed in each net cage.Throughout the three-month rearing period, the fish were fed with commercial pellets containing a crude protein of 28-30%, as much as five percent of the weight per day.Feed is given with a frequency of twice a day, every morning and evening.At the end of the rearing period, all fish were harvested, and then the parameters of weight, survival rate, and harvested biomass were measured and calculated.Fig. 1.The crosses of the five common carp strains followed the full diallel method.The diagonal squares colored represent the pure crosses of each strain, Note: Mj (Majalaya), Rj (Rajadanu), Wd (Wildan), St (Sutisna), Sy (Sinyonya)

Data analysis
The parameters observed were specific growth rate, survival rate, and harvested biomass of each cross-population.The specific growth rate was analyzed based on the average individual body weight of each population at harvest.The formula is: An analysis of variance (ANOVA) was used to examine the specific growth rate, survival rate, and harvested biomass of the different populations.An analysis of variance (ANOVA) was used to examine the specific growth rate, survival rate, and harvested biomass of the different populations.A correlation analysis among those three parameters was conducted to support the information.
The estimation of mid-parent heterosis for specific growth rate, survival rate, and harvested biomass follows [3]: (4) Note: RPS : The average performance of crossing and reciprocal population.

RIP
: The average performance of the parents.
Maternal effect and individual effect for specific growth rate, survival rate, and harvested biomass were analyzed by following [9]: The maternal effect of i-strain.

RPi
: The average performance of crossing populations with i-strain as the dam.

RIP
: The average performance of the parents.

IEi
: The individual effect Descriptive analysis was conducted to estimate heterosis, maternal effects, and individual effects within the crosses of common carp.

Result and discussion
The results of the analysis of variance (ANOVA) of phenotypic parameters, including specific growth rate, survival rate, and harvested biomass, were presented in Table 1.The results of the analysis indicate that the three culture parameters among 25 populations of common carp fish from crosses exhibited significant differences (P < 0.05).Based on these results, the analysis proceeded to examine the parameters related to heterosis values within the crosses of the measured traits, which was the primary focus of this research.The correlation between the specific growth rate, survival rate, and harvested biomass of the 25 hybrid common carp populations in this study was presented in Table 2.The correlation value of the three parameters was low, ranging from -0.091 -0.209.Phenotypic performance is a genetic expression that is influenced by environmental conditions.The same genotype may produce different phenotypic performances if cultured in different environments.Meanwhile, various genotypes will produce various phenotypic performances, even though maintenance in a similar environment [23,24,25].The phenotypic performance of the 25 crossbreed populations in this study was significantly different for all the observed characters: specific growth rate, survival rate, and harvested biomass.The populations resulting from crosses between strains will produce hybrid populations with different genotypes.Thus, the variation in the phenotypic performance of the 25 crossbred populations in this study is thought to be mainly due to genotype differences among populations.Differences in each parent's genotypes cause differences among populations resulting from crosses.[2] reported the genetic background of five common carp strains in Indonesia.Based on this report, the genetic differences of common carp strains originating in several different geographical areas are mostly affected by natural and artificial selection.This causes the genetic performance of each strain of the common carp to be specific.The genetic influence of each strain on these hybrid populations can be seen from the performance of the population compared to the performance of its parents.
The heterosis analysis of specific growth rate, survival rate, and harvested biomass characters is presented in Table 3. Heterosis of specific growth rate, survival rate, and harvested biomass ranged from -66.35 to 72.23, -82.26 to 61.91, and -77.63 to 223.48, respectively.
The combination of crosses with a high heterosis value in one character only sometimes has high heterosis in other characters (Table 3).This is due to the relatively small correlation between the three parameters, that is, -0.091 (between specific growth rate and survival rate), -0.119 (between specific growth rate and harvested biomass), and 0.209 (between survival rate and harvested biomass) (Table 2).The low correlation between specific growth and survival rates in this study was presumably because the population was crossbred with diverse genetic characteristics.The variation of genetic performance results in the expression of different phenotypes.This impacts the performance of the phenotypic character of each population, which is very diverse.The comparison of hybrid population performance compared to its parents is known as heterosis.[26,27] concluded that heterosis for growth is common but not universal in carp.Populations with a large dominant trait will usually have a tangible impact on the performance of their hybrid offspring.For example, a strain with a fast growth rate and a large dominant trait will produce a hybrid population that resembles the parent.In general, a hybrid populations performance tends to exhibit traits that between those of its two parent strains.However, the presence of over-dominant gene action in crosses between strains can cause the performance of a hybrid population to exceed the performance of both parents.This will result in a hybrid population that is much better than the average of the two parents and, in some cases, may even exceed the performance of the best parent [24].
The high diversity of the hybrid populations' phenotypic performance, indicated by the significant difference in the analysis of variance of the three observed parameters (Table 1), showed that the genetic variance of each hybrid population was also high.On the other hand, the low correlation value between these parameters indicates that the relationship between each parameter is relatively low.This has implications for the difficulty of choosing the best hybrid combination for cultural activities.This can be obtained if the survival value can be maintained high until the end of the culture [28]).In this study, the varying survival values caused the growth parameters not always to impact the biomass value of the harvested fish.However, the main objective of common carp culture is to reach the best yields so that the harvested biomass parameter can be used as the main parameter in selecting the best hybrid population.Associated with the value of improving the phenotypic performance of hybrid populations with their parents, several combinations of crosses with high heterosis values in this study, especially on harvested biomass as the productivity parameter, include crosses between Rajadanu female and Sutisna male, Rajadanu female and Majalaya male, Majalaya female and Sutisna male, Sinyonya female and Sutisna male, Sinyonya female and Majalaya male.
The influence of the maternal effect on the specific growth rate, survival rate, and harvested biomass of common carp cross populations in this study is presented in Figure 2  (A, B, C).The maternal-effect on the specific growth rate of the hybrid population was greater in the Sutisna and Majalaya strains (Fig. 2A).In both strains, the individual effect is very low.This result indicated that using both strain females in carp hybridization highly affected the hybrid performance.The maternal-effect on the survival of hybrid carp is relatively low (Figure 2B).Even though the maternal effect of the Majalaya strain in this study is the highest affected the survival rate of the hybrid carp.The two strains that have the maternal influence on the harvested biomass of hybrid carp are the Majalaya and Wildan strains (Figure 2C).In contrast to the growth rate's character, the harvested biomass of the female parent Sutisna has a relatively small effect.Based on the three analyzed characters, it seems that the Majalaya strain is a type of common carp with the potential as a female parent in the formation of hybrid carp for aquaculture purposes.
Besides being influenced by the genetic background of the parents, the phenotypic performance of the hybrid population is also influenced by the environment.One environmental factor influencing fish's early development is the maternal effect, including age, size, health, reproductive conditions, and others.In this study, the maternal effect was seen in the parameters of specific growth rate, survival rate, and harvested biomass of hybrid populations.The maternal effect was more visible in the Sutisna and Majalaya strains regarding specific growth rates.The selection of females of the two strains in the formation of hybrid fish is thought to affect the specific growth rate of the resulting hybrid fish.In the survival character, the maternal effect of the Majalaya strain was higher than that of other strains.In harvest biomass parameters, the maternal effect was seen as high in the Majalaya and Wildan strains.Based on the analysis of these three parameters, the selection of Majalaya carp as female broodstock needs to be considered because it greatly influences the performance of the specific growth rate, survival rate, and harvested biomass or productivity of the hybrid common carp population.

Conclusion
The cross combination of common carp with the highest heterosis value on the parameters of productivity is the cross of Rajadanu female and Sutisna male, Rajadanu female and Majalaya male, Majalaya female and Sutisna male, Sinyonya female and Sutisna male, Sinyonya female and Majalaya male.Meanwhile, using the Majalaya strain as the female parent significantly influenced the performance of the specific growth rate, survival, and harvest biomass/productivity of the hybrid carp fish produced.
rate.Wt : The average individual body weight at harvest.W0 : The average individual body weight in the first plot.T : Rearing period.Survival or survival rate (SR) is calculated using the formula: of fishThe harvested biomass was analyzed based on average of body weight and number of fish harvested.The formula is:Harvested Biomass (Kg) = Number of Fish Harvested × Average Weight per Fish(3)

Fig. 2 .
Fig. 2. Maternal and individual effect on growth rate (A), survival rate (B), and harvested biomass (C) of the common carp hybrid population

Table 1 .
Analysis of variance for aquaculture parameters of the 25 populations resulted from the crossing among five common carp strains.

Table 2 .
Correlation between specific growth rate, survival rate, and harvested biomass of the 25 populations resulted from the crossing among five common carp strains.

Table 3 .
Heterosis estimation for specific growth rate, survival rate, and harvested biomass of the 25 populations resulted from the crossing among five common carp strains.Bold values are the five crossing populations with the highest value of heterosis for each character.The first code of crossing is female: Rj (Rajadanu); St (Sutisna); Mj (Majalaya); Wd (Wildan); Sy (Sinyonya).