ABSTRACT: The tolerance of salinity and hardness was checked on the growth and survival of Nile tilapia (Oreochromis niloticus) in National Agriculture Research Council (NARC) Islamabad. Hormones of the neuroendocrine system are essential players in the control of osmoregulatory mechanisms, and extensive studies on endocrine pathways involved in osmoregulation clarified a significant role of prolactin (PRL) and growth hormone (G.H.) Part of the salinity work was done in South Africa, specifically on Oreochromis mossambicus, and we collected many of the different strains found throughout the country for evaluation and to develop a synthetic strain of O. mossambicus for commercial aquaculture in regions where the faster growing Nile tilapia was prohibited. As the salinity tolerance of tilapia fiy increases with size and survival is best at the size of maximum tolerance, Watanabe et al. Improving salinity tolerance in tilapias9 tilapia with a good growth rate and salinity tolerance, termed ND60. Again, growth rates were found to be slow compared to pure Nile Tilapia even when hybridised with Nile Tilapia. Tilapias have been introduced extensively to areas near the coast. Growing rapidly, these tilapia hybrids are easy to raise and have a high tolerance for salinity stress. transferring the salinity tolerance trait from one species to another through hybridization; > establishing molecular markers of salinity tolerance that will be used to identify species, populations and families for selective breeding. The same pattern of improved growth for genotypes with shorter alleles originating from the O. niloticus grandparental fish was demonstrated, although O. mossambicus is considered a more salt-tolerant species. Salinity tolerance of the tilapias Oreochromis aureus, O. niloticus and an O. mossambicus X O. niloticus hybrid. During tolerance testing, feeding was discontinued beginning on the day of the experiment. It has a central role in the adaptation of marine species to freshwater by reducing sodium-potassium ATPase activity and consequently increasing the osmotic level of the plasma. Even though they were able to venture out to the sea, they did not colonise or establish populations in the marine environment, so probably do not pose an biodiversity risk as David raised, otherwise they would have historically cultivated this habitat by now. Several genes that are differentially expressed in tilapia in saltwater and freshwater – beta haemoglobin, ATPase Ca2þ+ -transporting plasma membrane ATPase, pro-opiomelanocortin (all upregulated in saltwater) and beta-actin (downregulated) – were identified as candidate genes associated with salt tolerance. Differences in ion transporter type and membrane location on the chloride cells were also found between freshwater- and saltwater-challenged fish. Swansea University (Editor’s Note: This article was originally published in the November/December 2011 print edition of the Global Aquaculture Advocate. The emerging knowledge of quantitative trait loci associated with, or genes directly involved in saltwater tolerance may facili-tate marker-assisted or gene-assisted selection for this trait in tilapia in the future. Screening domesticated and natural populations, searching for genetic variations in the biochemical pathways that underlie the observed phenotypic differences, is another route. Most of the available data concern the role of gills in salt or water exchange. Tags. Finally, the application of genomic approaches and modern molecular biology techniques may enable the identification of genes that encode specific proteins active in salt-tolerant species that are lacking or less active in less-tolerant species, or specific proteins that are induced under salt stress. 20 & nbsp ; ‰ ) were evaluated during the study period 15 ppt ( per... Comes to saline tolerance, the Blue varieties can survive low salinity levels compared to pure Nile tilapia when! Tilapia even when hybridised with Nile tilapia was filtered by recirculation through a 6-cm bed of crushed shells! Tilapia grown in brackish and seawater systems as well as in fresh water into marine waters and potentially! Phenotypic differences, is another route by El-Zaeem et al to eight after... Ion transporter type and membrane location on the day of the world to look at a of! 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