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Avner Cnaani - Institute of Animal Science, Agricultural Research Organization, Volcani Center, PO Box 6, Bet Dagan 50250, Israel. 
Ariel Velan - Institute of Animal Science, Agricultural Research Organization, Volcani Center, PO Box 6, Bet Dagan 50250, Israel. 
Gideon Hulata - 
Institute of Animal Science, Agricultural Research Organization, Volcani Center, PO Box 6, Bet Dagan 50250, Israel

With increasing scarcity of fresh water available for aquaculture, especially in arid regions, development of tilapias that tolerate high salinity would increase fish (and hence, animal protein) production. We review culture practices, nutrition, physiology and genetics, and propose approaches to improving salinity tolerance in tilapias. Dietary supplementation with NaCl and optimized acclimation protocols are immediate and practical ways to improve salt tolerance. Inter-specific variation in salinity tolerance may be used to select salt-tolerant species and develop salt-tolerant hybrids. Physiological studies of biochemical pathways underlying phenotypic differences in salt tolerance can lead to genetic studies of intra- and inter-specific variation. Molecular technology can lead to studies on osmoregulation-related biochemical pathways, for which the euryhaline tilapia is an attractive model. Functional genomics and proteomics are powerful tools for studying the molecular bases of environmental adaptation and metabolic connections to osmoregulatory physiology. Both provide avenues for discovering novel pathways related to osmoregulation with relevance to aquaculture. In the long term, quantitative trait loci associated with, or genes involved in saltwater tolerance may facilitate marker-assisted or gene-assisted selection for this trait in tilapia.

We recently examined the possible interrelationships between the allelic polymorphism of the tilapia Prolactin gene and growth performance in brackish water. Comparative sequencing revealed one amino-acid substitution at a highly conserved site adjacent to the receptor binding site, where the conserved leucine in O. mossambicus is replaced by phenylalanine in O. niloticus. We also studied allelic variation in a microsatellite marker at the promoter region of the Prolactin 1 gene. Two distinct alleles in O. niloticus as well as two additional alleles in O. mossambicus were detected. Parental

crossing was performed between O. mossambicus and O. niloticus in search for correlations between the allelic composition and growth performance of F2 families in brackish water. Correlation between genotypes (allelic composition) and growth performance was found in some but not all families. One allele appears to be associated with good growth in brackish water.

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IMPROVING SALINITY TOLERANCE IN TILAPIAS: A REVIEW

Avner Cnaani - Institute of Animal Science, Agricultural Research Organization, Volcani Center, PO Box 6, Bet Dagan 50250, Israel. 
Ariel Velan - Institute of Animal Science, Agricultural Research Organization, Volcani Center, PO Box 6, Bet Dagan 50250, Israel. 
Gideon Hulata - 
Institute of Animal Science, Agricultural Research Organization, Volcani Center, PO Box 6, Bet Dagan 50250, Israel

With increasing scarcity of fresh water available for aquaculture, especially in arid regions, development of tilapias that tolerate high salinity would increase fish (and hence, animal protein) production. We review culture practices, nutrition, physiology and genetics, and propose approaches to improving salinity tolerance in tilapias. Dietary supplementation with NaCl and optimized acclimation protocols are immediate and practical ways to improve salt tolerance. Inter-specific variation in salinity tolerance may be used to select salt-tolerant species and develop salt-tolerant hybrids. Physiological studies of biochemical pathways underlying phenotypic differences in salt tolerance can lead to genetic studies of intra- and inter-specific variation. Molecular technology can lead to studies on osmoregulation-related biochemical pathways, for which the euryhaline tilapia is an attractive model. Functional genomics and proteomics are powerful tools for studying the molecular bases of environmental adaptation and metabolic connections to osmoregulatory physiology. Both provide avenues for discovering novel pathways related to osmoregulation with relevance to aquaculture. In the long term, quantitative trait loci associated with, or genes involved in saltwater tolerance may facilitate marker-assisted or gene-assisted selection for this trait in tilapia.

We recently examined the possible interrelationships between the allelic polymorphism of the tilapia Prolactin gene and growth performance in brackish water. Comparative sequencing revealed one amino-acid substitution at a highly conserved site adjacent to the receptor binding site, where the conserved leucine in O. mossambicus is replaced by phenylalanine in O. niloticus. We also studied allelic variation in a microsatellite marker at the promoter region of the Prolactin 1 gene. Two distinct alleles in O. niloticus as well as two additional alleles in O. mossambicus were detected. Parental

crossing was performed between O. mossambicus and O. niloticus in search for correlations between the allelic composition and growth performance of F2 families in brackish water. Correlation between genotypes (allelic composition) and growth performance was found in some but not all families. One allele appears to be associated with good growth in brackish water.

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