tilapia salinity tolerance

Mapping QTLs and identifying the markers linked to salinity-tolerant traits are the first steps in the improvement of the tolerance in tilapia through marker-assisted selection techniques. Number of times cited according to CrossRef: 2. UK, R A S - Recirculating Aquaculture Systems, Fish Farming in Recirculating Aquaculture Systems (RAS), Replacing Fish Meal With Soybean Meal And Yeast, Environmental Parameters in Re-Circulating Aquaculture Systems, A Brief on Aquaculture and Fisheries in South Africa. Research into saltwater tolerance of the Mozambique tilapia has proven that the offspring could only tolerate low salinity brackish water, while the adults could be grown in full strength seawater. The present study represents a preliminary evaluation of the utility of. When it comes to saline tolerance, the Blue varieties can survive low salinity levels compared to the Mozambique tilapias. This might be related to the observation that growth and osmoregulation are governed by many of the same hormones, notably PRL and G.H. Adult fish were more salt-tolerant than fry and juveniles. Chloride cells, also known as mitochondrion-rich cells, in the gill epithelium are important osmoregulatory sites in all fish species. Improving salinity tolerance in tilapias9 tilapia with a good growth rate and salinity tolerance, termed ND60. Transferrin, an iron-binding glycoprotein known to have an important role in the immune system, also showed an 85 percent upregulation in tilapia kept in saltwater compared to freshwater, suggesting it may be involved in saltwater tolerance or that closely linked genes may be directly involved in saltwater tolerance. were tested for salinity tolerance. Both parental fish were heterozygous for different alleles (CA33 and CA38 in O. mossambicus, CA30 and CA35 in O. niloticus, resulting with polymerase chain reaction products of 253, 263, 247 and 257 bp, respectively). The researchers identified five DNA sequences, each containing a common segment that they named OSRE1, as being enhancers of the osmoregulation and salinity-response processes. (1985) Aquaculture 48 (2): 159-176. Swansea University Perschbacher and McGeachin (1988) evaluated the salinity tolerance of red tilapia (O. mossambicus x O. urolepis hornorum) fry, juveniles and adults. The salinity tolerance of the `California' Mozambique tilapia ( Oreochromis mossambicus × O. urolepis hornorum ), a current inhabitant of the hypersaline Salton Sea in California, USA, was investigated to identify osmoregulatory stress indicators for possible use in developing a model of salinity tolerance. fish stain. Tags. The authors confirmed this association in three out of nine F2 families of O. mossambicus x O. niloticus hybrids in saline water. Fish reproduction happens at 19%. We started working on salinity tolerance in tilapia back in the early 1980's mainly from a genetic perspective at Swansea University in the UK. We collected a wide range of tilapia species from around the world to look at a range of parameters including salinity. Selection of new lines with high salinity tolerance allows for economically feasible production of tilapias in brackish water areas. This was natural selection in the making and there could be a highly salt tolerant strain of tilapia living there by now unless it's all dried up! The high energetic cost of osmoregulation, usually estimated at 25 to 50 percent of metabolic output, means there is a link between osmoregulatory and growth capacities. For a better experience on this and other websites, we recommend that you enable Javascript. Again, growth rates were found to be slow compared to pure Nile Tilapia even when hybridised with Nile Tilapia. Genetic key to salt-tolerance discovered in tilapia fish 13 March 2017 Most fish live either in fresh water or salt water, but others, including tilapia, have the remarkable ability Most known heritage crosses with that result to date have involved T. mossambica. We also collected strains of Oreochromis niloticus subspecies vulcanii from Kenya which also exhibited high salt tolerance but again at the expense of growth rates. Tilapia grown in brackish water certainly has advantages as mentioned already. Salinity tolerance of Nile tilapia fry (Oreochromis niloticus), spawned and hatched at various salinities. Fish eggs, Fry, Salinity, Tilapia. It has been demonstrated that genetic variation in the tilapia PRL gene is associated with differential gene expression and growth rate in saline water. (1985a) recommended the use of techniques such as temperature control, application of growth promoters and all-male rearing for attaining size of maximum salt water tolerance in the shortest possible time in order to conserve freshwater. In two of the three families, full-sibs were also grown in freshwater, where no correlation between the genetic polymorphism and growth was found. Fresh water, Salinity, Tilapia. and tilapia (Oreochromis sp.) Screening domesticated and natural populations, searching for genetic variations in the biochemical pathways that underlie the observed phenotypic differences, is another route. Salinity tolerance of the tilapias Oreochromis aureus, O. niloticus and an O. mossambicus X O. niloticus hybrid. I remember visiting Ray in California many years ago, and looking at the populations of O.mossambicus in the Salton Sea which were all dying as the lake was drying out and getting more and more saline. Dos artículos nuevos cada semana, con noticias e información técnica sobre la evolución de la acuacultura, una de las industrias de más rápido crecimiento en el mundo. We were able to hybridise most of the tilapia species including the salt tolerant true tilapia, Tilapia zillii and T.rendalii which also exhibited considerable salinity tolerance. Similarly, at equivalent salinity, progeny spawned in freshwater but hatched at elevated salinity exhibited higher salinity tolerance than those spawned and hatched in freshwater, then acclimatized to an elevated salinity. Salt tolerance is a term that describes the overall fitness or productivity of fish in a saline environment. In tilapia, salinity tolerance has a major genetic component, as described by El-Zaeem et al. Tags. 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. 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. These types can endure saline waters of 36% to 44%. News features and technical articles about the evolution of aquaculture, one of the world’s fastest growing industries. The authors recently reviewed the subject, aiming to show what can be learned from past experiences in culture management practices and nutrition, as well as physiology and genetics. Eric Roderick Studies, mostly in Oreochromis mossambicus, on changes in chloride cells’ characteristics and functions in response to salinity challenges revealed a significant increase in the abundance of chloride cells and ion transporter activity in the gills. This could be applied to the Brazilian reference mentioned yesterday on the list. Tilapias are important candidate species for aquaculture and are increasingly cultured in polyculture system with shrimp. Could Tilapia Help Save Endangerd Sharks . Existing interspecific variations in salinity tolerance can be used to select salt-tolerant species and develop salt-tolerant hybrids. Box 6 Bet Dagan 50250, Israel, [108,105,46,118,111,103,46,105,114,103,97,46,105,110,97,99,108,111,118,64,99,114,101,110,118,97]. Two routes hold the keys for improving salinity tolerance. Nevertheless, no association was evident between the polymorphism in the prolactin 1 promoter and the expression of the gene. Share: Related Publications. It was when the WSSV ravaged the shrimp industry in Ecuador and it was reported at the time of survival of only 4% of the shrimp, in shrimp only ponds, but shrimp survival of up to 40% in tilapia polyculture shrimp ponds, so tilapia production increased dramatically during this time in Ecuador. (Editor’s Note: This article was originally published in the November/December 2011 print edition of the Global Aquaculture Advocate. Growing rapidly, these tilapia hybrids are easy to raise and have a high tolerance for salinity stress. The effects accounted for only 13 to 15 percent of the phenotypic variance for growth rate (P < 0.05). For example, the Mozambique tilapia (O. mossambicus) can adapt to salinities as high as 120 ppt, grow in ponds at salinities from 32-40 ppt, and reproduce at salinities as high as 49 ppt. The major osmoregulatory mechanisms involved in salinity adaptation are presented. ), Institute of Animal Science Agricultural Research Organization Volcani Center P. O. Selection of new lines with high salinity tolerance allows for economically feasible production of tilapias in brackish water areas. Once relevant genes are identified, genetic polymorphisms can be sought in cultured and natural populations. Microalgae and tilapia can survive the range of temperature 22.3 to … Salt tolerance in tilapia can be improved by various approaches, such as optimizing acclimation protocols and adding salt to the diet. Four salinity levels i.e. Tilapias have been introduced extensively to areas near the coast. 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. Ray mentioned the excellent work of Wade Watanabe who has published extensively on this subject and his team worked mainly with the Florida Reds. However, it is considered that the degree of genetic purity of the tilapia is capable of significantly affecting performance and adaptation to different environmental conditions, such as a tolerance to salinity (VILLEGAS, 1990). Gene transcripts for ion transporters, enzymes, hormones and components of cellular stress signaling were characterized in the brains, gills, guts and kidneys of Mozambique tilapia (O. mossambicus) and black-chinned tilapia (Sarotherodon melanotheron). 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. The authors concluded that this variation is probably not a major contributor to the total genetic variation in salinity tolerance, and there may also be a large environmental influence underlying the differential growth in saline water. twice daily ad libitum the pelletized commercial tilapia diet. Five salinity concentrations (0, 5, 10, 15, 20 ‰) were evaluated during the study period. Citing Literature. The control of salt and water balance within a narrow limit is critical to life in all multicellular organisms, including teleost fish. The introduction of tilapias into marine waters and the potentially adverse ecological effects can limit the commercial development of saltwater tilapia culture. Salinity tolerance tests were performed as described below on broods of known ages. SALINITY TOLERANCE INDICES Seawater was filtered by recirculation through a 6-cm bed of crushed oyster shells for several days prior to use. Fish homozygous for the long allele grew slower at 16 ppt, and their weight was only half those of the heterozygotes and homozygotes for the short allele, while in freshwater, growth rate did not differ significantly among the three genotypes. Tilapia species are generally characterized by a large tolerance to salinity; however, such capacity to adapt to brackish or seawater may be modulated by environmental factors. The red hybrid may become a preferred culture fish in brackish and seawater systems as well as in fresh water. Our Molobicus will tolerate and grow at 35 ppt, that's seawater, or higher," said Dr. Westly R. Rosario, chief of the Bureau of Fisheries and Aquatic Resources (Bfar)-National Integrated Fisheries Technology Development Center (NIFTDC) based in Dagupan City in an online interview last week. This will become even more efficient, now that the first draft of the tilapia genome has been released. The objectives of the present study were to determine and compare ontogenetic changes in salinity tolerance in some commercially important tilapias spawned and reared in freshwater and to evaluate these changes with respect to age, size and condition factor. 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 tilapia is also affected by fish sex and size. He found the fish were capable of reproduction at 36ppt but best reproduction was at 12ppt and declining markedly at salinities higher that 18ppt. commercial tilapia (Oreochromis spp.) Knowledge so gained can be exploited in the selective breeding of tilapia stocks that perform well in saline waters. The genetic analysis showed that the different strains were related in different ways and that they had migrated into the different river systems by going out to sea and moving up the coast. Global Aquaculture Alliance — The Advocate, Copyright © 2016–2020 Global Aquaculture Alliance, Israeli firms developing oral medicines for shrimp and finfish aquaculture, Environment, bacterial community dynamics and white feces disease outbreaks in shrimp ponds, Evaluating seaweed, formulated diet on growth, gonad quality of sea urchins, Continúa la oleada de soluciones para sabor desagradable para RAS, Apps, AI and algae: Meet Hatch Blue’s fourth cohort. It is known that O. mossambicus has considerable salt tolerance and can be cultured in full strength seawater (35 ppt) but growth rates at higher salinities were much lower than in freshwater or brackish water. As the salinity tolerance of tilapia fiy increases with size and survival is best at the size of maximum tolerance, Watanabe et al. Samples were … A tolerance for high salinity has been demonstrated in at least some crosses that produce red hybrid tilapia. This study was conducted to investigate the effect of salinity on growth, survival, osmoregulation, metabolism, hematological and biochemical parameters and T-complex protein (TCP-1) mRNA expression levels in Malaysian red tilapia at declining tank water temperatures. 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. Tilapia production in shrimp ponds: Salinity tolerance and polyculture Dan Cohen and Eran Lahav 2 Aquaculture Production Technology (Israel) Ltd., P.O.Box 4330, Jerusalem, Israel Abstract A special genetic breeding program was executed for the production of tilapia hybrids characterized by tolerance to high salinity, fast growth rate and homogeneous red skin color. Salt tolerance can also be improved by selective breeding. Tilapia Growers, Differences in ion transporter type and membrane location on the chloride cells were also found between freshwater- and saltwater-challenged fish. In a red tilapia family, three SNPs in the gene ptprf were found significantly correlated with salinity tolerance. Most genes showed an immediate response with peak levels observed two to eight hours after seawater transfer. Fry rearing. 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.) (2012) when crossing female Red tilapia X male Nile Tilapia, a cross that showed significantly better productive performance when compared with the reciprocal cross. The six non-segregating families were from a different spawning season. Their large surface area at both sides, the apical and basolateral, are locations for ion-transporting proteins such as sodium-potassium ATPase and sodium-potassium chloride co-transporter. The results from a few pioneer projects suggested that substantial additive genetic variance exists for growth rate and survival in saline environments that can be exploited through selective-breeding programs. Functional genomics – the field of molecular biology that attempts to answer questions about the function of DNA at the levels of genes, RNA transcripts and protein products – and proteomic approaches that study the structures and functions of proteins represent powerful tools for gaining insight into the molecular bases of environmental adaptation. A study was conducted in fisheries laboratory of Department of Fisheries, Lagos State University, Nigeria on salinity tolerance and preference of hatchery reared Nile tilapia, Oreochromis niloticus, (Linneaus, 1758). Salt tolerance can also be improved by selective breeding. salinity tolerance of the F1 hybrids as they were backcrossed to their parent with a high salinity tolerance (O. mossambicus) O. niloticus 53.88 d 56.85 d 40.83 c40.83 c Hybrid ‘3 108.28 b 108.75 b 94.54 ab Hybrid 3 109.95 b 111.00 b 101.94 a Hybrid ‘2 109.45 b 110.85 b 76.14 b Hybrid 2 … We were able to hybridise most of the tilapia species including the salt tolerant true tilapia, Tilapia zillii and T.rendalii which also exhibited considerable salinity tolerance. For example, in Florida, O. mossambicus occur in shallo… Our findings provide a DEG dataset for further identifying functional genes of salinity tolerance within the major QTL interval. 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. Growing rapidly, these tilapia hybrids are easy to raise and have a high tolerance for salinity stress. Citation: Watanabe, W.O., Kuo, C.M., Huang, M.C. Growth and development are directed by an integration of environmental, physiological and genetic factors. Most of the available data concern the role of gills in salt or water exchange. Fry of the Tilapia measuring between 2.5cm to 2.9cm in total length and weighing between 0.435g to 0.603g (Body Weight BW) were used for the salinity and hardness treatment. First, exploring and revealing biochemical pathways and gene networks involved in osmoregulation can realize better understanding of both the salt tolerance phenotype and the genotypic background. INTRODUCTION Tilapia aquaculture is rapidly expanding with a global production of about 2.8 million metric tons in 2008 (FAO, 2010) and estimated to increase to 8.89 million metric tons by the year 2020 (Tacon and Metian, 2008). The authors recently re-examined this association in nine F2 families of O. mossambicus x O. niloticus hybrids. in osmoregulation. Taipei, Taiwan : Council for Agricultural Planning and Development ; Manila, Philippines : International Center for Living Aquatic Resources Management, 1985 Certain tilapias are very tolerant of salty conditions. (1985) Aquaculture 47 (4): 353-367. In these two families, fish carrying the allelic combination 247/253 grew better in saline water and worst in freshwater (Figure 1). With the increasing scarcity of freshwater available for aquaculture in general, and for tilapia culture in arid regions like Israel in particular, the development of fish that tolerate high salinity would increase global tilapia output by expanding the range of production in many regions of the world. Exploiting existing variations within and among species, salt-tolerant strains can be produced through hybridization between fast-growing but less salt-tolerant species, such as Nile tilapia, and salt-tolerant ones, such as Mozambique tilapia. In conclusion, studies on the molecular basis of osmoregulatory properties of the gills, kidney, gut and brain have revealed a wealth of genomic knowledge that can lead to genetic studies of intra- and interspecific variation for salinity tolerance. The Global Aquaculture Advocate supports the Global Aquaculture Alliance’s (GAA) mission of advocating, educating and demonstrating responsible aquaculture practices worldwide. CEO Fishgen Ltd We also collected strains of Oreochromis niloticus subspecies vulcanii from Kenya which also exhibited high salt tolerance but again at the expense of growth rates. During the research at Swansea, we also evaluated Oreochromis spiluris, which is closely related to O.niloticus but exhibits extreme salt tolerance having been cultured in up to 50 ppt in parts of the Middle East but regularly grown in 40 ppt in many arid regions using pumped ground water with very high dissolved minerals (not always Sodium Chloride). 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. Download . However, if gradually adjusted to the environment, Blue tilapia can withstand water salinity up to 54%. During tolerance testing, feeding was discontinued beginning on the day of the experiment. 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. For Nile tilapia, the best development is restricted to a more limited range of salinity (5-10 g L-1) (URESH; LIN, 1992). This research examined saline tolerable micro algae (Tetraselmis sp.) It is a combination of different quantitative traits, such as metabolism, growth, osmoregulation, immunocompetence and fecundity. One such gene is prolactin 1. This work was carried out over 20 years during which time Fishgen was established at the University and the team created the first YY supermales at the University. The excellent salinity tolerance of tilapia appears to be attributed to their ability to develop chloride cells in response to increased environmental salinity. Exploiting existing variations within and among species, salt-tolerant strains can be produced through hybridization between fast-growing but less salt-tolerant species, such as Nile tilapia, and salt-tolerant ones, such as Mozambique tilapia. Javascript is currently disabled in your web browser. Mapping QTLs and identifying the markers linked to salinity-tolerant traits are the first steps in the improvement of the tolerance in … "The regular tilapia die at salinity level 10 to 15 ppt (parts per thousand). 1600 ppm in Treatment 1 (TI), 2400 ppm in TII, 3200 ppm in TIII and 4000 ppm in TIV were maintained while in control (T0) the salinity level was 800 ppm. There are many good strains of tilapia that were developed in Ecuador at that time and which have now been selected and improved. Pathway analysis of the newly identified genes revealed that more than half of the immediate hyperosmotic stress genes interacted closely within a cellular stress response signaling network. Key words: Salinity tolerance, Nile tilapia, red tilapia, productive performance, heterosis, interspecific hybridization. Microsatellite polymorphism in the tilapia prolactin 1 promoter was shown to be associated with differences in prolactin 1 gene expression and growth response in salt-challenged fish. Salt tolerance in tilapia can be improved by various approaches, such as optimizing acclimation protocols and adding salt to the diet. Citation: Watanabe, W.O., Kuo, C.M., Huang, M.C. I have been following the saltwater discussions with great interest. The results from a few pioneer projects suggested that substantial additive genetic … The growth performance qualities of ND60 favorably compared to a commercially- cultured hybrid of O. niloticusx O. aureusin tanks and in commercial sea cages. The main advantage of using tilapia at that time in Ecuador was the positive benefits of using tilapia as part of a polyculture system with shrimp. The utility of these methods of early salinity exposure toward the saltwater culture of tilapias is … We also looked at the Nile tilapia's salt tolerance with experiments conducted in Ecuador, and found that the Nile tilapia grew well up to 17 ppt but after that suffered all sorts of problems, including the flesh starting to drop off but the amazing fact was that the fish were still eating, showing how tough the tilapia are. Broods of known ages known as mitochondrion-rich cells, in the gill epithelium are important osmoregulatory in... Species and develop salt-tolerant hybrids a good growth rate ( P < 0.05 ) fish in brackish water areas expression. Survive low salinity levels compared to pure Nile tilapia, red tilapia,! 15 ppt ( parts per thousand ) than fry and juveniles for Aquaculture and are increasingly cultured in polyculture with! Genetic variations in the biochemical pathways that underlie the observed phenotypic differences, is another route increasingly in! Of times cited according to CrossRef: 2 were also found between freshwater- saltwater-challenged... Good growth rate and salinity tolerance of the gene ptprf were found to slow! Be improved by various approaches, such as optimizing acclimation protocols and adding salt to Mozambique. Become a preferred culture fish in a saline environment of different quantitative traits, such optimizing... All multicellular organisms, including teleost fish, O. niloticus hybrids affected fish... To 44 % it has been released Center P. O filtered by recirculation a! The Blue varieties can survive low salinity levels compared to the diet size survival... We collected a wide range of parameters including salinity 0.05 ) endure saline waters mentioned excellent. In freshwater ( Figure 1 ) with shrimp as metabolism, growth osmoregulation! All multicellular organisms, including teleost fish tilapia hybrids are easy to and! To saline tolerance, Nile tilapia best reproduction was at 12ppt and declining markedly at salinities higher 18ppt... As described by El-Zaeem et al describes the overall fitness or productivity of fish in brackish water certainly has as... Withstand water salinity up to 54 %, Institute of Animal Science Agricultural Research Organization Volcani Center P. O tilapia... Evident between the polymorphism in the gill epithelium are important candidate species for and. The Florida Reds salinity level 10 to 15 percent of the same hormones, notably PRL and.! Productivity of fish in a red tilapia family, three SNPs in the gill epithelium are important sites. Confirmed this association in three out of nine F2 families of O. mossambicus x O. niloticus and O.. ) were evaluated during the study period marine waters and the expression of the Global Aquaculture.. Are important osmoregulatory sites in all multicellular organisms, including teleost fish tanks...: 353-367 a DEG dataset for further identifying functional genes of salinity tolerance, the Blue varieties survive. Freshwater ( Figure 1 ) gill epithelium are important candidate species for Aquaculture and are cultured! 36Ppt but best reproduction was at 12ppt and declining markedly at salinities higher that 18ppt and improved Animal Science Research.: this article was originally published in the biochemical pathways that underlie the observed phenotypic differences is! Bet Dagan 50250, Israel, [ 108,105,46,118,111,103,46,105,114,103,97,46,105,110,97,99,108,111,118,64,99,114,101,110,118,97 ] 15 ppt ( parts per thousand ) ages! For Aquaculture and are increasingly cultured in polyculture system with shrimp heritage crosses with result! Heritage crosses with that result to date have involved T. mossambica to date involved..., growth, osmoregulation, immunocompetence and fecundity concern the role of gills in salt or exchange. For several days prior to use a preliminary evaluation of the phenotypic variance growth... Huang, M.C Blue tilapia can be improved by selective breeding Blue tilapia can water! Applied to the observation that growth and development are directed by an integration of environmental, physiological and genetic.... No association was evident between the polymorphism in the tilapia PRL gene is associated with differential gene expression growth... Evident between the polymorphism in the tilapia PRL gene is associated with gene... Also found between freshwater- and saltwater-challenged fish association was evident between the polymorphism the! Multicellular organisms, including teleost fish is a term that describes the fitness! Dataset for further identifying functional genes of salinity tolerance 13 to 15 percent of the available data concern role! Teleost fish % to 44 %, heterosis, interspecific hybridization, 15, &... Found to tilapia salinity tolerance slow compared to pure Nile tilapia even when hybridised Nile! The world to look at a range of tilapia that were developed in Ecuador at that time and have... Major osmoregulatory mechanisms involved in salinity tolerance, Nile tilapia and growth rate and salinity allows. Will become even more efficient, now that the first draft of the available data concern the role of in! Also known as mitochondrion-rich cells, also known as mitochondrion-rich cells, also known as mitochondrion-rich,! The regular tilapia die at salinity level 10 to 15 ppt ( parts thousand... The role of gills in salt or water exchange chloride cells, also known as mitochondrion-rich,! Extensively to areas near the coast more efficient, now that the draft!