GENOTYPE BY ENVIRONMENT INTERACTION FOR PRODUCTIVITY TRAITS OF A HYBRID TILAPIA IN FRESH AND BRACKISH WATER PONDS

Introduction

Shrimp production is the most important aquaculture industry in Indonesia with the highest contribution to the national income (MMAF, 2018). However, recurrent farming failures and increasing production losses caused by disease outbreaks have hampered the growth of shrimp production, and driven Indonesian shrimp farmers to add tilapia as a second species. The Research Institute for Fish Breeding (RIFB) is developing a fast-growing salinity tolerant tilapia strain. A fresh water nucleus-based program is the simplest strategy to implement but requires knowledge on the extent of genotype by environment (GxE) interaction between fresh and brackish water environments to ensure that genetic improvement in the nucleus transfers to production systems in brackish water. The objectives of this study were: 1) to investigate the presence of GxE between fresh and brackish water ponds, and 2) to estimate genetic parameters for fresh and brackish water environments.

Materials and methods

We produced 91 fish families, and randomly choose 2 groups of 20 fingerlings that we PIT tagged and communally grown in brackish and freshwater ponds (120-147 days). We recorded stocking weight( SW), harvest weight (HW) and standard length (L) at harvest and calculated daily growth coefficient (DGC,(Trọng et al., 2013)) and growth rate in length (GR(L)) from these data. We estimated descriptive statistics using R, and estimated genetic parameters by fitting a series of bivariate animal models in ASReml (Gilmour et al., 2015).

Results

All observed trait of HW, L, DGC and GR (L) at harvest were higher in brackish water and significantly different (P<0.05) compared to freshwater (Table 1). The estimates of additive genetic variance (), heritability (h2) and GCV within freshwater and brackish water for HW, L, DGC and GR (L) are shown in Table 2. Genetic variances and heritability estimates for all traits in freshwater were lower compared to the brackish water, except L. The h2 estimates for HW, L, DGC, and GR (L) were moderate (0.35 – 0.43). In the freshwater pond, h2 estimates of HW and L were higher compared to the brackish water while for DGC and GR (L), h2 estimates were higher in the brackish water compared to the freshwater. The genetic correlation () for all observed trait between freshwater and brackish water were moderate, ranging from 0.65 – 0.74.

Discussion

RIFB has been developing this strain based on selection for own performance (mass selection) for growth and survival in brackish water ponds for 4 generations. However, this breeding scheme has several drawbacks including high mortality of selection candidates during the grow out period in unpredictable salinity condition; security issues; and mortality during transport and adaptation of candidates to the nucleus site in freshwater. Evaluating selection candidates in freshwater ponds and select on sib performance in brackish water could mitigate some of these complications and challenges. However, if G×E interactions are strong, this approach could result in reduced genetic gain due to inaccurate selection of breeding candidates in freshwater (Mulder & Bijma, 2005). In this study, our estimates genetic correlations between fresh and brackish water for HW, SL, DGC and GR(L) were 0.65-0.74 which suggests substantial re-ranking of genotypes between the two environments, suggesting that it is essential to incorporate information from full-sibs in brackish water into the genetic evaluation. Our results also show that HW, L, DGC and GR (L) in brackish water are greater than in freshwater, indicating that the Sukamandi strain has a high salinity tolerance. This is most likely because this strain is a unique composite of Nile tilapia with introgressed salinity tolerance genes from blue tilapia (Yu et al., 2021). The moderate heritabilities for all production-related traits (0.35-0.50) indicate the presence of sufficient additive genetic variance for future selection.

Conclusions

There is GxE interaction between brackish water and freshwater and a breeding program with the brood stock selection process in freshwater should incorporate the sib information of growth performance in brackish water.

References

Gilmour, A. R., Gogel, B. J., Cullis, B. R., Welham, S. J., & Thompson, R. (2015). ASReml User Guide Release 4.1 Functional Specification. VSN International Ltd. www.vsni.co.uk.

MMAF. (2018). Marine and Fisheries in Figures 2018. The Center for Data, Statistics and Information. Ministry of Marine Affairs and Fisheries of the Republic of Indonesia.

Mulder, H. A., & Bijma, P. (2005). Effects of genotype x environment interaction on genetic gain in breeding programs. J Anim Sci, 83(1), 49-61. https://doi.org/10.2527/2005.83149x

Trọng, T. Q., van Arendonk, J. A. M., & Komen, H. (2013). Genetic parameters for reproductive traits in female Nile tilapia (Oreochromis niloticus): II. Fecundity and fertility. Aquaculture, 416-417, 72-77. https://doi.org/https://doi.org/10.1016/j.aquaculture.2013.08.031

Yu, X., Setyawan, P., Bastiaansen, J. W. M., Liu, L., Imron, I., Groenen, M. A. M., Komen, H., & Megens, H.-J. (2021). Genomic analysis of saline tolerant Nile tilapia strain shows signatures of selection ad introgression from blue tilapia (Oreochromis aureus). Aquaculture, Manuscript Number: AQUACULTURE-D-21-03754