Salinity--stress and Desiccation in Intertidal Worms

SYNOPSIS. Intertidal worms (oligochaetes, polychaetes, sipunculids)inhabiting beaches and tidal fiats both on the open sea coastand in estuaries may be exposed to significant tidal as wellas seasonal variations in salinity. However, there are veryfew measurements of the actual variations in salinity encounteredby worms in nature. Behavior (irrigation of burrow, verticalmovements in burrows, migration in gradients of salinity)maybe important in determining to which of the available salinitiesin a tidal cycle the worms may be exposed. In response to rapidlowering of salinity, worms gain water and lose salts, theseprocesses combining in diluting the internal fluids. Internalilution occurs more slowly in euryhaline species than in stenohalinespecies. Worms fully adapted to salinities lower than 30 % seawater may be hyperosmotic (demonstrated for six species of Nereidae).Mechanisms involved in hyperosmotic regulation include activetransport of salts(demonstrated in Nereis diversicolor), reductionofthe permeability of the body surface to salts and perhapsto water, and perhaps production of hypo—osmotic urine.Sipunculids can tolerate considerable loss of water rom dehydrationand concomitant increases in osmotic concentration of the bodyfluids. It is suggested that worms exposed to significant tidalvariations in salinity may seldom be in osmotic equilibriumwith their external medium.     

Acute osmotic tolerance of cultured cells of the oyster pathogen Perkinsus marinus (Apicomplexa : Perkinsida)

Cultured Perkinsus marinus cells were exposed for 24 hr to salinities of 0, 3, 6, 9, 12 and 22 ppt at temperatures of 1, 5, 10, 15 and 28°C in artificial seawater (ASW) and to the same salinities at 28°C in ASW with the osmotic concentration adjusted with sucrose to the equivalent of 22 ppt. At 28°C mortality increased as salinity decreased below 22 ppt. Mortality was greater than 99% at 0 ppt and greater than 90% at 3 ppt. Mortality was 70% at 6 ppt, 43% at 9 ppt and 20% at 12 ppt. Mortality was low (<5%) and equal to that at 22 ppt in all treatments where osmotic concentration was maintained with sucrose. Mortality occurred rapidly, within 5 min of exposure to experimental conditions. In the region where mortality was most sensitive to salinity changes (6–12 ppt), lower temperature caused an increase in mortality, but the temperature effect was significant only at 9 ppt.     

The effects of rapid salinity change on in vivo arginine kinase flux in the juvenile blue crab,Callinectes sapidus

The effect of acclimation salinity and salinity changes on the concentration of high-energy phosphate metabolites and arginine kinase (AK) flux was examined in vivo in juvenile blue crabs using 31P-nuclear magnetic resonance (NMR). Crabs were acclimated for 7 days to a salinity of 5 or 35 per thousand and then placed in a flow apparatus that could sustain the animals while NMR spectra were acquired. Crabs were subjected to either hyperosmotic salinity changes, where an animal acclimated to 5 per thousand was exposed to a salinity of 35 per thousand, or hyposmotic changes, which involved the reciprocal exchange. Neither acclimation salinity nor salinity change had a significant effect on the concentrations of arginine phosphate, inorganic phosphate or ATP. 31P-NMR saturation transfer experiments were used to determine the effect of salinity on the forward and reverse flux of the AK reaction. There was no significant effect of acclimation salinity or salinity change on the flux rate through this reaction. This is in contrast to previous results, which showed that AK flux in isolated muscle was sensitive to prevailing osmotic conditions (Holt and Kinsey, J. Exp. Biol. 205 (2002) 1775-1785). The present study indicates that the integrated osmoregulatory capacity of the intact animal is sufficient to preserve cellular energy status and enzyme function during acute salinity changes.     

Osmotic and Ionic Regulation of North American Zebra Mussels (Dreissena polymorpha)

SYNOPSIS. Unlike other freshwater bivalves that survive formonths in deionized water, Dreissena polymorpha requires minimalconcentrations of Na, K, Mg, and Cl in the bathing medium forlong-term survival. Although ion transport rates are higherin D. polymorpha compared to other freshwater bivalves, theytend to have lower blood solute concentrations. D. polymorphahas an unusually "leaky" epithelium with a high paracellularpermeability to solutes. Thus, even with high transport rates,it may not be possible for zebra mussels to retain higher bloodsolutes because of the extensive passive loss of ions. Undera hyperosmotic stress, D. polymorpha will rapidly osmoconform(about 12 hr) due primarily to the diffusion of solutes andpartially to the osmotic loss of water. D. polymorpha is notcapable of surviving an imbalance of Na/K in the external medium.In the absence of K the cells will tend to lose volume to achieveisosmotic balance with the blood, but the animals usually diewithin a few days. If D. polymorpha is exposed to excess K inthe environment (1 mM), they will accumulate K in the blood.If the K enters the cells, cellular volume would expand dueto increase in osmolyte concentration, yet, if K remains inthe blood, there will be an electrochemical imbalance. In eithercase, the animal cannot survive much longer than a day. WhenNa and K are present in the medium in a balanced combinationapproximated by artificial seawater (ASW), D. polymorpha willsurvive an acute transfer to 100 mosm ASW indefinitely (months).Our preliminary studies have shown that D. polymorpha will toleratestep-wise acclimation to solutions >250 mosm provided thechanges in salinity do not exceed 50–100 mosm. Freshwaterbivalves, unlike the marine bivalves, have limited free aminoacids in their body fluids and must rely on inorganic ions forosmotic regulation. The free amino acids serve as an importantosmolyte buffer for volume regulation when an animal experiencesan environment of changing salinity. The inability of Dreissena,and perhaps other freshwater bivalves, to tolerate hyperosmoticallyinduced dehydration may be due, in part, to the inability toaccumulate or retain sufficient intracellular K to facilitateregulatory volume adjustments.     

Calreticulin is crucial for calcium homeostasis mediated adaptation and survival of thick ascending limb of Henle's loop cells under osmotic stress

The thick ascending limb of Henle's loop (TALH) is normally exposed to variable and often very high osmotic stress and involves different mechanisms to counteract this stress. ER resident calcium binding proteins especially calreticulin (CALR) play an important role in different stress balance mechanisms. To investigate the role of CALR in renal epithelial cells adaptation and survival under osmotic stress, two-dimensional fluorescence difference gel electrophoresis combined with mass spectrometry and functional proteomics were performed. CALR expression was significantly altered in TALH cells exposed to osmotic stress, whereas renal inner medullary collecting duct cells and interstitial cells exposed to hyperosmotic stress showed no significant changes in CALR expression. Moreover, a time dependent downregulation of CALR was accompanied with continuous change in the level of free intracellular calcium. Inhibition of the calcium release, through IP3R antagonist, prevented CALR expression alteration under hyperosmotic stress, whereas the cell viability was significantly impaired. Overexpression of wild type CALR in TALH cells resulted in significant decrease in cell viability under hyperosmotic stress. In contrast, the hyperosmotic stress did not have any effect on cells overexpressing the CALR mutant, lacking the calcium-binding domain. Silencing CALR with siRNA significantly improved the cell survival under osmotic stress conditions. Taken together, our data clearly highlight the crucial role of CALR and its calcium-binding role in TALH adaptation and survival under osmotic stress.     

Secretion of water and ions by malpighian tubules of larval mosquitoes: effects of diuretic factors, second messengers, and salinity

The effects of changes in the salinity of the rearing medium on Malpighian tubule fluid secretion and ion transport were examined in larvae of the freshwater mosquito Aedes aegypti and the saltwater species Ochlerotatus taeniorhynchus. For unstimulated tubules of both species, the K(+) concentration of secreted fluid was significantly lower when larvae were reared in 30% or 100% seawater (O. taeniorhynchus only), relative to tubules from freshwater-reared larvae. The Na(+) concentration of secreted fluid from unstimulated tubules of O. taeniorhynchus reared in 30% or 100% seawater was higher relative to tubules from freshwater-reared larvae. The results suggest that changes in salinity of the larval rearing medium lead to sustained changes in ion transport mechanisms in unstimulated tubules. Furthermore, alterations of K(+) transport may be utilized to either conserve Na(+) under freshwater (Na(+)-deprived) conditions or eliminate more Na(+) in saline (Na(+)-rich) conditions. The secretagogues cyclic AMP [cAMP], cyclic GMP [cGMP], leucokinin-VIII, and thapsigargin stimulated fluid secretion by tubules of both species. Cyclic AMP increased K(+) concentration and decreased Na(+) concentration in the fluid secreted by tubules isolated from O. taeniorhynchus larvae reared in 100% seawater. Interactions between rearing salinity and cGMP actions were similar to those for cAMP. Leucokinin-VIII and thapsigargin had no effect on secreted fluid Na(+) or K(+) concentrations. Results indicate that changes in rearing medium salinity affect the nature and extent of stimulation of fluid and ion secretion by secretagogues.     

The Role of Glycerol and Inorganic Ions in Osmoregulatory Responses of the Euryhaline Flagellate Chlamydomonas pulsatilla Wollenweber

The green euryhaline flagellate Chlamydomonas pulsatilla Wollenweber, isolated from a coastal marine environment, was grown exponentially over the salinity range of 10 to 200% artificial seawater (ASW). The cellular volume and aqueous space of the alga, measured by [¹⁴C] mannitol and ³H₂O tracer analyses of centrifuged cell pellets, ranged between 2.3 and 3.1 picoliters and between 1.5 and 2.1 picoliters, respectively. The nonaqueous space determined in those analyses (28-35%) was consistent with the cell composition of the alga. The glycerol content of the alga increased almost linearly with increasing salinity; its contribution to intracellular osmolality at 200% ASW was about 57%. The contribution of amino acids and soluble carbohydrates to the cell osmotic balance was small. Intracellular ion concentrations determined by analyzing centrifuged cell pellets of known [¹⁴C]mannitol space by atomic absorption spectrophotometry, and by neutron activation analyses of washed cells were similar. At 10% ASW, potassium and magnesium were the major cations, and chloride and phosphate were the major anions. The sodium and chloride content of the alga increased with increasing salinity; at 200% ASW the intracellular concentration of both sodium and chloride was about 400 millimolar. The intracellular osmolality (π_int) matched closely the external osmolality (π_ext) over the entire salinity range except at 10% ASW where π_int exceeded π_ext by 120 to 270 milliosmoles per kilogram H₂O.     

Exposure to fluctuating salinity enhances free amino acid accumulation inTigriopus californicus (Copepoda)

Summary Intracellular concentrations of free amino acids (FAA) in the intertidal copepodTigriopus californicus increase in response to hyperosmotic stress and decrease in response to hypo-osmotic stress. The purpose of this study was to determine if exposure to repeated bouts of osmotic stress resulted in changes in FAA accumulation or the degree of FAA retention in subsequent episodes. Five groups ofT. californicus were exposed for 22 days to a fluctuating salinity regime which consisted of 24 h at 100% seawater followed by 24 h at either 90, 80, 70, 60 or 50% seawater (11 cycles). After the tenth exposure to 100% seawater, individuals from each treatment group were analyzed for alanine and proline concentration. Alanine and proline accumulation generally increased in proportion to the osmotic stress up to 60–100% seawater — additional osmotic stress failed to increase total accumulation. Prior exposure to fluctuating salinity increased the extent of alanine and proline retention observed upon transfer to a hypo-osmotic medium. The treatment group which had experienced the most extreme fluctuation (50–100% seawater) retained alanine and proline levels approximately 10- and 20-fold higher, respectively, than controls. A less severe salinity fluctuation was required to elicit this response for alanine (90–100% seawater) than for proline (60–100% seawater). Previous exposure to fluctuating salinity also resulted in increased alanine and proline accumulation in subsequent episodes of hyperosmotic stress. 24 h after transfer from 50 to 100% seawater, alanine and proline levels in the conditioned copepods were approximately 3- and 7-fold higher, respectively, than in copepods which had not been cycled. This facilitation in alanine and proline accumulation occurred after 10 and 11 cycles, respectively. Of the increased accumulation in alanine and proline, 7.0% and 22.5%, respectively, could be accounted for by the higher degree of FAA retention while under hypo-osmotic conditions.Abbreviation FAA free amino acids     

Multimarker response to salinity stress in two estuarine bivalves of different genetic diversity: Mya arenaria and Limecola balthica from the Gulf of Gdańsk (southern Baltic Sea)

The estuarine bivalves Limecola balthica and Mya arenaria are common inhabitants of marine soft bottom habitats in the Northern Hemisphere. Both species are able to live under a wide range of environmental conditions including variable salinity. However, in L. balthica there is high genetic variability, and populations are often genetically adapted to local conditions. By contrast, genetic diversity in M. arenaria is low across the species’ geographic range, which attests to acclimatization to different conditions. We hypothesized that individuals of M. arenaria should perform better under osmotic stress. We tested this hypothesis by performing a 5‐week experiment that exposed individuals of both clam species to hypo‐ and hyperosmotic conditions. A multiple biomarker approach that included physiological, biochemical, and histological markers was used to assess bivalve performance. Exposure to the different salinities induced biological responses that particularly affected respiratory activity in both species tested, but these responses were much more pronounced in individuals of L. balthica. The results confirmed the hypothesis that the phenotypic plasticity of M. arenaria was more pronounced and reflected a different strategy of adapting to heterogeneous habitats.     

Growth hormone transgenesis affects osmoregulation and energy metabolism in zebrafish (Danio rerio)

Growth hormone (GH) transgenic fish are at a critical step for possible approval for commercialization. Since this hormone is related to salinity tolerance in fish, our main goal was to verify whether the osmoregulatory capacity of the stenohaline zebrafish (Danio rerio) would be modified by GH-transgenesis. For this, we transferred GH-transgenic zebrafish (T) from freshwater to 11 ppt salinity and analyzed survival as well as relative changes in gene expression. Results show an increased mortality in T versus non-transgenic (NT) fish, suggesting an impaired mechanism of osmotic acclimation in T. The salinity effect on expression of genes related to osmoregulation, the somatotropic axis and energy metabolism was evaluated in gills and liver of T and NT. Genes coding for Na⁺, K⁺-ATPase, H⁺-ATPase, plasma carbonic anhydrase and cytosolic carbonic anhydrase were up-regulated in gills of transgenics in freshwater. The growth hormone receptor gene was down-regulated in gills and liver of both NT and T exposed to 11 ppt salinity, while insulin-like growth factor-1 was down-regulated in liver of NT and in gills of T exposed to 11 ppt salinity. In transgenics, all osmoregulation-related genes and the citrate synthase gene were down-regulated in gills of fish exposed to 11 ppt salinity, while lactate dehydrogenase expression was up-regulated in liver. Na⁺, K⁺-ATPase activity was higher in gills of T exposed to 11 ppt salinity as well as the whole body content of Na⁺. Increased ATP content was observed in gills of both NT and T exposed to 11 ppt salinity, being statistically higher in T than NT. Taking altogether, these findings support the hypothesis that GH-transgenesis increases Na⁺ import capacity and energetic demand, promoting an unfavorable osmotic and energetic physiological status and making this transgenic fish intolerant of hyperosmotic environments.     

Impact of anisosmotic conditions on structural and functional integrity of cumulus-oocyte complexes at the germinal vesicle stage in the domestic cat

During cryopreservation, the immature oocyte is subjected to anisosmotic conditions potentially impairing subsequent nuclear and cytoplasmic maturation in vitro. In preparation for cryopreservation protocols and to characterize osmotic tolerance, cat cumulus-oocyte complexes (COC) at the germinal vesicle (GV) stage were exposed for 15 min to sucrose solutions ranging from 100 to 2,000 mOsm and then examined for structural integrity and developmental competence in vitro. Osmolarities > or =200 and < or =750 mOsm had no effect on incidence of oocyte nuclear maturation, fertilization success, and blastocyst formation compared to control COC (exposed to 290 mOsm). This relatively high osmotic tolerance of the immature cat oocyte appeared to arise from a remarkable stability of the GV chromatin structure as well as plasticity in mitochondrial distribution, membrane integrity, and ability to maintain cumulus-oocyte communications. Osmolarities <200 mOsm only damaged cumulus cell membrane integrity, which contributed to poor nuclear maturation but ultimately had no adverse effect on blastocyst formation in vitro. Osmolarities >750 mOsm compromised nuclear maturation and blastocyst formation in vitro via disruption of cumulus-oocyte communications, an effect that could be mitigated through 1,500 mOsm by adding cytochalasin B to the hyperosmotic solutions. These results (1) demonstrate, for the first time, the expansive osmotic tolerance of the immature cat oocyte, (2) characterize the fundamental role of cumulus-oocyte communications when tolerance limits are exceeded, and (3) reveal an interesting hyperosmotic tolerance of the immature oocyte that can be increased two-fold by supplementation with cytochalasin B.     

Physiological effects of saline waters on zander

Rapid transfer of zander Stizostedion lucioperca to hypoosmotic brackish water (mean osmolality 230 mOsmol kg–1 , c. 8 psu) significantly increased plasma chloride concentrations after 24 h compared to those transferred to fresh water, although plasma osmolality was not significantly affected. After 6 days, plasma osmolality was slightly elevated but stable plasma glucose and cortisol concentrations and blood haematocrit and haemoglobin suggest a lack of hormonal stress responses and resultant secondary effects. Rapid transfer of zander to a more saline environment, hyperosmotic to plasma (mean osmolality 462 mOsmol kg^‐1, c. 16 psu) induced a greater increase in plasma osmolality and chloride concentrations within 24 h, with a further rise after 6 days exposure, but all fish maintained a state of hypo‐osmoregulation both 24 h and 6 days after transfer. The initial osmotic disturbance (at 24 h) was accompanied by increased plasma glucose, blood haematocrit and haemoglobin and a decreased mean cell haemoglobin concentration (MCHC), suggesting an adrenergic stress response, but these parameters fully recovered within 6 days of exposure to this hyperosmotic environment with MCHC rising to exceed the level in freshwater fish. Zander did not survive rapid transfer to more hyperosmotic conditions (750 or 1001 mOsmol kg^‐1, 26‐35 psu), but they did survive exposure to simulated‘tidal cycles’ of rising and declining salinity, peaking after 6 h at c. 29 or 33 psu. Although osmotic disturbance was apparent after 6 h exposure and other physiological parameters suggested both adrenergic and corticosteroid components of a stress response, rapid recovery was apparent after return to fresh water. The results indicate that the zander, a non‐indigenous species in the U.K., has a high level of osmotic tolerance and a degree of hypo‐osmoregulation in saline environments not found in most stenohaline freshwater teleosts. This osmoregulatory ability could enable invasion of new U.K. river systems by using inshore marine environments of low salinity as saltwater bridges.     

FREEZING STRESS AND OSMOTIC DEHYDRATION IN FUCUS DISTICHUS (PHAEOPHYTA): EVIDENCE FOR PHYSIOLOGICAL SIMILARITY1

The effects of osmotic dehydration and freezing on photosynthesis were studied in the brown alga Fucus distichus L. The data indicated that F. distichus exhibits similar physiological responses to both osmotic dehydration and freezing stress and that these responses resemble those in the literature for the effect of desiccation in air. Both stresses inhibited light-limited (P_subsat) and light-saturated (P_max) photosynthesis measured immediately after plants were reimmersed in seawater. The degree of initial inhibition and subsequent recovery of photosynthesis were proportional to the severity of the dehydration or freezing treatment. P_subsat and P_max recovered completely from osmotic dehydration for 3 h in 200% and 3 hr at – 10°C, but recovery was only partial following 3 h in 300%o or 3 h at – 15°C. In most cases, recovery was complete within 2 h following dehydration, with little further recovery occurring between 2 and 24 h posttreatment. No time-dependent recovery occurred following severe freezing. Observations using the vital stain fluorescein diacetate suggested that the lack of complete recovery might be due to severe damage or death of a proportion of cells in the thallus. There were no clear effects of either osmotic dehydration or freezing on dark respiration (R_d), although R_d was stimulated in all emersed treatments (frozen plants and 5° C controls) immediately following reimmersion. Measurement of chlorophyll fluorescence induction kinetics indicated that both osmotic dehydration and freezing reduced the ratio of variable to maximum florescence (F_v/F_m), indicating a decrease in the quantum efficiency of photosystem I. Based on these data, we suggest that there are common cellular and physiological components involved in the response of fucoid algae to a range of water stresses. This hypothesis was supported by experiments that showed that osmoacclimation in hyperosmotic seawater (51%o)for 2 weeks increased the ability of F. distichus to recover from freezing at – 15° C. During acclimation, mannitol content increased under hyperosmotic conditions and decreased under hypoosmotic conditions. Changes in plasma membrane integrity, determined by fresh weight: dry weight ratio, and amino acid release following freezing indicated an increasing gradient of freezing tolerance from low to high salinity. However, none of these physiological changes fully explained the marked increase in the freezing tolerance of photosynthesis observed in plants acclimated under hyperosmotic conditions.     

Osmoregulation in juvenile Rhabdosargus holubi (Steindachner) (Teleostei: Sparidae)

Juvenile Rhabdosargus holubi (Steindachner), one of the commonest teleosts in south east African estuaries, are strong osmoregulators, showing little change in their internal osmotic concentration over an extremely wide salinity range. In 35‰ seawater the internal osmotic concentration is held at 370 mosmol/1. At a salinity of 1‰ the internal osmotic concentration falls to 216 mosmol/1 and at a salinity of 65‰ rises to 381 mosmol/1. When exposed to a new salinity the internal osmotic concentration does not change until after 10 h; this may be of considerable importance to fish living in areas subject to short term changes of salinity.     

Ionic and acid-base consequences of exposure to increased salinity in the zebra mussel, Dreissena polymorpha

Dreissena polymorpha, an invasive freshwater bivalve, displays physiological characteristics that reflect its ancestry in brackish water, yet it has limited ability to withstand modest increases in salinity. We examined changes in hemolymph ion concentrations and acid-base variables in mussels transferred to and incubated in 10% artificial seawater (ASW) for 7 days and then returned to pondwater (PW) for a further 7 days. Hemolymph was sampled (10 animals per sample period) every 4 h for the first 24-h incubation and at 72 h and 168 h for both the transfer to 10% ASW and the transfer back to PW. The initial response to transfer to 10% ASW was a rapid attainment of an apparent isoosmotic steady state, with most hemolymph ion concentrations rising and attaining steady state within 12 h. Hemolymph magnesium rose more slowly, and hemolymph calcium declined despite an increase in its concentration in the bathing medium. Hemolymph pH rose significantly during the first 24 h, from 7.96 to 8.25, as a result of increases in bicarbonate; pH subsequently returned to normal through increases in PCO2. When animals were returned to PW after 7 days' incubation in ASW, the response of the major hemolymph ions was largely the reverse of that effected by the transfer to ASW. Hemolymph pH was not altered significantly until after 72 h in PW, when declines in bicarbonate lowered the pH to 7.73. Strong ion difference (SID) was related significantly to hemolymph pH. Hemolymph calcium and magnesium showed a reciprocal relationship throughout both transfer and incubation. Solubility interactions between sulfate and calcium and magnesium may be important in determining calcium availability in solution. The Na/K ratio in hemolymph was maintained within relatively narrow bounds throughout the procedure and may contribute to the mussels' ability to volume-regulate during an osmotic challenge. Overall, the responses of D. polymorpha to modest changes in salinity were largely the result of passive processes.     

Proline overproduction in cells of the green alga Nannochloris bacillaris resistant to azetidine-2-carboxylic acid

Abstract Cells of N. bacillaris have been selected that are resistant to the toxic proline analogue azetidine-2-carboxylic acid (A2C) in 7% artificial seawater (ASW). This phenotype is stable in the absence of selection pressure. A2C resistance at low salinity was demonstrated to be due to an overproduction of proline in these cells, while levels of other amino acids were unaffected. Both wild-type and A2C-resistant cells respond to growth in high salinity media (100% ASW, 200% ASW) by accumulation of proline, but proline levels at all salinities are higher in the A2C-resistant cells than in the wild-type. Proline overproduction in the A2C-resislant cells did not affect fluctuations in the levels of other salinity-dependent solutes, such as homarine. A mutant with this level of specificity over a wide range of water potentials has not been reported for other plants and algae. Both the wild-type and A2C-resistant cells were able to grow over the entire salinity range tested (7%-300% ASW). However, the A2C-resistant cells showed a lower division rate than the wild-type in 300% ASW, and yield of A2C-resislant cells was lower than yield of wild-type cells at the salinity extremes (7% ASW, 300% ASW). The response or wild-type and A2C-resistant cells to rapid increases in salinity were similar for both growth and photosynthesis. The presence of a constitutive high level of proline in the A2C-resistant cell line did not confer any obvious increased tolerance to salinity shocks, indicating that there are other important factors in the biochemical adaptation to salinity in these cells.     

Effects of salinity on growth and survival in five Artemia franciscana (Anostraca: Artemiidae) populations from Mexico Pacific Coast

Salinity is an important factor influencing growth and survival of aquatic organisms such as Artemia, a valuable aquaculture species. This study evaluated the effects of salinity on A. franciscana populations from different water bodies in Mexico's Pacific Coast. With this purpose, five autochthonous bisexual Artemia populations were tested to assess their survival and growth values against salinities of 40, 60, 80, 100 and 120 g/l, under laboratory conditions (25 +/- 2 degrees C; pH 8-10; constant light and aeration). The organisms were fed with 100 mL of rice bran and 2L of Tetraselmis suecica (500 000 cel/ml). The culture experiments were made in 200L plastic tanks, and survival and growth final values were obtained after 21 culture days. Survival and growth curves were determined by a regression analysis (R2). The significant differences between salinities were determined by ANOVA test (p < 0.05). The best survival and growth rates were found at salinities of 100-120 g/l. When the Mexican Artemia populations were cultivated at 40 g/l of salinity, 100% mortality was observed in the juvenile stage. This study determined that survival and growth values of A. franciscana populations increased with salinity. The five A. franciscana populations presented significant differences in their survival rate under various salinity regimes. The studied populations experienced high mortality at salinities under 60 g/l and over 200 g/l, and especially during the metanauplius stage. The present study confirms that growth rates in Mexican A. franciscana populations from Pacific Coast habitats are not inversely proportional to salinity. These A. franciscana populations should be cultured at 100-120 g/l of salinity to obtain better survival and growth rates. This data is useful to improve culture systems in aquaculture biomass production systems.