The effects of temperature and salinity on the swimming ability of whiteleg shrimp, Litopenaeus vannamei

Swimming endurance of whiteleg shrimp, Litopenaeus vannamei exposed to various temperatures (15, 20, and 25 degrees C) and salinities (15, 32, and 40 per thousand) was determined in a swimming channel against one of five flow velocities (5.41, 6.78, 8.21, 10.11, and 11.47 cm s(-1)) for up to 9000 s. No shrimp swam the full 9000 s throughout the experiment. The swimming endurance decreased as swimming speed was increased at any of the temperatures and salinities tested and was significantly affected by temperature and salinity (P<0.05). The power model (nu x t(b) = a) showed a better fit to the relationship between swimming endurance (t, in s) and swimming speed (nu, in cm s(-1)) at any of the temperatures and salinities tested. The swimming ability index (SAI), defined as SAI = integral(0)(9000) vdt x 10(-4) (cm), was found to be temperature- and salinity-dependent in L. vannamei. The optimum temperature and salinity and corresponding maximum SAI were Topt = 21.3 degrees C and SAI(max21.3) = 7.37 cm; Sopt = 27.6 per thousand and SAI(max27.6) = 7.47 cm, respectively. The range of temperatures and salinities within which SAI is >90% of the maximum was estimated between 17.6 and 24.9 degrees C and between 18.5 and 36.7 per thousand, respectively. The results suggest that the power model fits well to the observed endurance estimates and the SAI is a good index to quantitatively describe the overall swimming ability of L. vannamei. Furthermore, temperature and salinity can limit the swimming performance of L. vannamei.     

Effect of salinity on transmission of necrotizing hepatopancreatitis bacterium (NHPB) to Kona stock Litopenaeus vannamei

Elevated salinity and temperature have been observed prior to devastating necrotizing hepatopancreatitis (NHP) outbreaks in several geographically isolated shrimp ponds. These observations have led to the hypothesis that the NHP-bacterium (NHPB) is hindered by reduced salinity, even though the mechanism is not understood. The objective of this research was to examine the effect of salinity on transmission of NHPB. The transmission rate of NHPB was estimated through laboratory experiments whereby individuals of Kona stock Litopenaeus vannamei were orally exposed to a dead NHPB-infected shrimp. For each replicate, 12 susceptible shrimp were placed with a dead NHPB-infected shrimp in a 1 m2 bottom area cylindrical tank maintained at 30 degrees C for a period of 24 h. Four salinities of 10, 20, 30, and 40 per thousand were replicated 2 times in 2 trials, giving a total of 192 shrimp exposed per os to infective material. In each trial, a negative control group was included at each salinity, giving a total of 96 shrimp exposed orally to uninfected material. After the 24 h exposure period, susceptible shrimp were individually isolated at the same physical conditions for up to 60 d to determine NHPB transmission. The NHPB was transmissible regardless of salinity: nearly a quarter of susceptible shrimp exposed to NHPB at the lowest (10 per thousand) and highest (40 per thousand) salinity examined acquired NHPB. Transmission rates were highest at the intermediate salinities of 20 and 30 per thousand, suggesting that those salinities are optimal for NHPB transmission. The observed association between high salinity and NHP outbreak in a shrimp pond is not explained by these results because reduced transmission occurred at very low and very high salinities.     

Physiological and behavioral responses of the mud snails Hydrobia glyca and Hydrobia ulvae to extreme water temperatures and salinities: implications for their spatial distribution within a system of temperate lagoons

Physiological responses (oxygen consumption) and behavioral responses (feeding and activity) of the mud snails Hydrobia ulvae and Hydrobia glyca at different salinities (20 per thousand-80 per thousand) and temperatures (20 degrees and 30 degrees C) were studied. After 24 h under experimental conditions, both Hydrobia species already showed maximal activities (>90%) for a wide salinity range (30 per thousand-70 per thousand), with significant differences in activity between species only outside the usual salinity range of the studied lagoon. In contrast, egestion rates of H. glyca were significantly higher at the lowest salinities tested (30 per thousand and 40 per thousand) irrespective of water temperature, whereas egestion rates of H. ulvae were always significantly higher (57% on average) at 20 degrees C than at 30 degrees C and at the usual salinities found in the field (40 per thousand and 50 per thousand). Both species showed an oxyregulatory response to dissolved oxygen concentrations ranging from saturation to 1.5 mg O(2) L(-1), although specific oxygen consumption rates were significantly higher at 30 degrees C than at 20 degrees C (Q(10)=1.47+/-0.08 for H. ulvae and Q(10)=12.1+/-0.06 for H. glyca) and at the lowest salinities (30 per thousand-50 per thousand for H. ulvae and 30 per thousand-40 per thousand for H. glyca). On average, specific rates were higher for the smaller-sized H. glyca (1.64+/-0.03 microg O(2) mg(-1) ash-free dry weight [AFDW]) than for H. ulvae (1.35+/-0.03 microg O(2) mg(-1) AFDW). Despite the overlapping of their tolerances to high temperatures and salinities, the observed interspecies differences could play a certain role in the distribution of H. ulvae and H. glyca in the studied habitat. In particular, the decreasing feeding activity but increasing respiration of H. ulvae at 30 degrees C for salinities that usually occur in the studied lagoon could represent disadvantages to H. glyca during the warm period.     

Change in water temperature on the immune response of Taiwan abalone Haliotis diversicolor supertexta and its susceptibility to Vibrio parahaemolyticus

Taiwan abalones, Haliotis diversicolor supertexta, held in 30 parts/per thousand seawater at 28 degrees C, were injected with TSB-grown Vibrio parahaemolyticus (1.6x10(5) cfu abalone(-1)) and then transferred to 20, 24, 28 and 32 degrees C. All abalones transferred to 32 degrees C died by 72 h. The mortality of V. parahaemolyticus-injected abalone held at 20 and 24 degrees C was significantly lower over 24-96 h, compared to animals held at 28 and 32 degrees C. In a separate experiment designed to measure immune function, abalones held in 30 per thousand seawater at 28 degrees C and then transferred to 20, 24, 28 and 32 degrees C were examined for total haemocyte count, phenoloxidase activity, respiratory burst, and phagocytic activity to V. parahaemolyticus after 24, 72 and 120 h. The phenoloxidase activity and phagocytic activity decreased significantly, whereas respiratory burst increased significantly in abalone transferred to 32 degrees C. It is concluded that transfer of abalone from 28 degrees C to 32 degrees C reduced their innate immunity and resistance against V. parahaemolyticus infection.     

Oxygen consumption and osmoregulatory capacity in Neomysis integer reduce competition for resources among mysid shrimp in a temperate estuary

Results of field surveys and laboratory measurements of oxygen consumption and body fluid osmolality at different salinities in the mysids Neomysis integer, Mesopodopsis slabberi, and Rhopalophthalmus mediterraneus from the Guadalquivir estuary (southwest Spain) were used to test the hypothesis that osmotic stress (oxygen consumption vs. isosmotic points) was lowest at salinities that field distributions suggest are optimal. The three species showed overlapping spatial distributions within the estuary but clear segregation along the salinity gradient: N. integer, M. slabberi, and R. mediterraneus displayed maximal densities at lower, intermediate, and higher salinities, respectively. Adults of N. integer were extremely efficient hyperregulators (isosmotic point 30 per thousand) over the full salinity range tested (3 per thousand-32 per thousand), and their oxygen consumption rates were independent of salinity; adults of M. slabberi were strong hyper- and hyporegulators at salinities between 7 per thousand and 29 per thousand (isosmotic point, 21 per thousand) and showed higher oxygen consumptions at the lowest salinity (6 per thousand); adults of R. mediterraneus hyperregulated at salinities between 19 per thousand and seawater (isosmotic point, 36 per thousand), with the lowest oxygen consumption at salinity around their isosmotic point (35 per thousand). Thus, the osmoregulation capabilities of M. slabberi and R. mediterraneus seem to determine the salinity ranges in which most of their adults live, but this is not so for adults of N. integer. Moreover, maximal field densities of M. slabberi (males and females) and R. mediterraneus (males) occur at the same salinities as the lowest oxygen consumption. In contrast, field distribution of N. integer was clearly biased toward the lower end of the salinity ranges within which it osmoregulated. We hypothesize that the greater euryhalinity of N. integer makes it possible for this species to avoid competition with R. mediterraneus by inhabiting the more stressful oligohaline zone.     

Plasma osmolyte concentrations and rectal gland mass of bull sharks Carcharhinus leucas, captured along a salinity gradient

Bull sharks (Carcharhinus leucas) were captured across a salinity gradient from freshwater (FW) to seawater (SW). Across all salinities, C. leucas were hyperosmotic to the environment. Plasma osmolarity in FW-captured animals (642 +/- 7 mosM) was significantly reduced compared to SW-captured animals (1067 +/- 21 mosM). In FW animals, sodium, chloride and urea were 208 +/- 3, 203 +/- 3 and 192 +/- 2 mmol l(-1), respectively. Plasma sodium, chloride and urea in SW-captured C. leucas were 289 +/- 3, 296 +/- 6 and 370 +/- 10 mmol l(-1), respectively. The increase in plasma osmolarity between FW and SW was not linear. Between FW (3 mosM) and 24 per thousand SW (676 mosM), plasma osmolarity increased by 22% or 0.92% per 1 per thousand rise in salinity. Between 24 per thousand and 33 per thousand, plasma osmolarity increased by 33% or 4.7% per 1 per thousand rise in salinity, largely due to a sharp increase in plasma urea between 28 per thousand and 33 per thousand. C. leucas moving between FW and SW appear to be faced with three major osmoregulatory challenges, these occur between 0-10 per thousand, 11-20 per thousand and 21-33 per thousand. A comparison between C. leucas captured in FW and estuarine environments (20-28 per thousand ) in the Brisbane River revealed no difference in the mass of rectal glands between these animals. However, a comparison of rectal gland mass between FW animals captured in the Brisbane River and Rio San Juan/Lake Nicaragua showed that animals in the latter system had a significantly smaller rectal gland mass at a given length than animals in the Brisbane River. The physiological challenges and mechanisms required for C. leucas moving between FW and SW, as well as the ecological implications of these data are discussed.     

Effects of temperature and salinity on nitrogenous excretion by Litopenaeus vannamei juveniles

Excretion rates of ammonia-N, nitrite-N, nitrate-N, and dissolved organic nitrogen (DON) for juvenile Litopenaeus vannamei (3.85+/-0.83 g) were quantified in response to nine different combinations of temperature (24, 28, and 32 degrees C) and salinity (10, 25, and 40 ppt) under laboratory conditions. Results indicated that L. vannamei is ammonotelic, with ammonia-N accounting for 61.9-84.3% of total nitrogen (TN) excretion. There were significant effects of temperature and salinity, but no significant interaction between them, on ammonia-N excretion rate (R(AN)). R(AN) increased with increasing temperature, over the interval 24-32 degrees C. R(AN) was lower at 25 ppt than at 10 and 40 ppt, at all temperatures. DON excretion rate (R(DON)) was not significantly influenced by either temperature or salinity; the overall mean R(DON) was about 5.24 μg-N g -1 h -1. However, the percentages of DON in TN (P(DON)) varied from 15.4 to 36.4% under the various temperature-salinity combinations. P(DON) at 28 and 32 degrees C was significantly lower than at 24 degrees C, and P(DON) at 10 ppt was significantly lower than at 25 and 40 ppt. Only very small amounts of nitrogen were excreted by L. vannamei as nitrite-N and nitrate-N.     

Adaptive shifts in osmoregulatory strategy and the invasion of freshwater by brachyuran crabs: evidence from Dilocarcinus pagei (Trichodactylidae)

To evaluate putative adaptive changes underpinning the invasion of freshwater by the Brachyura, this investigation examines anisosmotic extra and isosmotic intracellular osmoregulatory capabilities in Dilocarcinus pagei, a neotropical, hololimnetic crab, including its embryonic and juvenile phases. All ontogenetic stages show a remarkable ability to survive a high salinity medium (25 per thousand, 750 mOsm/kg H2O, 350 mm Na+, 400 mM Cl-). Adults hyper-regulate hemolymph osmolality up to isosmoticity at 744 mOsm kg/H2O (24 per thousand), [Na+] and [Cl-] becoming isoionic at 449 (22 per thousand) and 256 mM (16 per thousand), respectively. Hemolymph (420+/-39 mOsm/kg H2O) and urine (384+/-44 mOsm/kg H2O) are isosmotic in adults held in freshwater, and after 5-days exposure to 25 per thousand (787+/-9 mOsm/kg H2O and 777+/-43 mOs/kg H2O, respectively); D. pagei does not produce dilute urine. Total free amino acid (FAA) concentrations in embryos (14.9+/-1.2), juveniles (32.8+/-0.1) and adult muscle (10.9+/-2.1 mmol/kg wet weight) in freshwater are 30-fold less than in brackish/marine Crustacea, suggesting that FAA constitute a useful parameter to evaluate adaptation to freshwater. On acclimation to 25 per thousand, total FAA increase by approximately 100% in embryos and in adult muscle and nerve tissue and hemolymph, owing to large increases in proline, arginine and/or alanine. However, effective FAA contribution to intracellular osmolality increases only in embryos, from 3 to 4.5%. These findings suggest that gill-based, anisosmotic extracellular regulation has supplanted isosmotic intracellular regulatory mechanisms during the conquest of freshwater by the Brachyura, and indicate that D. pagei may be an old, well-adapted inhabitant of this biotope.     

Effects of reduced salinity on survival, growth, reproductive success, and energetics of the euryhaline polychaete Capitella sp. I

Physiological adjustment to water of reduced salinity requires energy expenditure. In this study we sought to determine the fitness costs associated with such adjustment in the euryhaline polychaete Capitella sp. I, and the extent to which such costs could be explained by increased rates of energy expenditure. In a series of experiments conducted at 20 degrees C, salinity was reduced from 30 per thousand to either 25, 20, 15, 12, or 10 per thousand within 72 h after the larvae had been induced to metamorphose. Juveniles were reared on fine, organic-rich sediment. Over the next 15-30 days, we determined survival, growth, fecundity, and rates of respiration and feeding (via fecal pellet production). Larval salinity tolerance was also determined. Juvenile survival at salinities as low as 12-15 per thousand was comparable to that at 30 per thousand. The lower limit of salinity tolerance was 10-12 per thousand at 20 degrees C for both larvae and juveniles. Juveniles grew significantly more slowly at 12-15 per thousand in six of the seven experiments. Fecundity, however, was generally highest at intermediate salinities of 20-25 per thousand, and comparable at 30 and 15 per thousand. No individuals released embryos at 12 per thousand over the approximately 30-day observation periods in any of the three experiments in which the worms were reared at this low salinity. Reduced growth rates were not explained by differences in rates of respiration at different salinities: at reduced salinity, respiration rates were either statistically equivalent to (P>0.10) or significantly below (P<0.05) those recorded for animals maintained at 30 per thousand. Lower growth rates at lower salinities were best explained by reduced feeding rates. Further studies are required to determine whether digestive efficiency, growth hormone concentrations, or reproductive hormone concentrations are also altered by low salinity in this species.     

The Ontogeny of Osmoregulation and Its Neurosecretory Control In the Decapod Crustacean, Rhithropanopeus harrisii (Gould)

Laboratory-hatched larvae of this estuarine crab were rearedat 25°C in seawater of 25 salinity for 18 days coveringzoeal Stages I to IV and a megalops. Three-day periods betweenzoeal stages represent intermolt stages of circadean metecdysis,diecdysis, and proecdysis.Larvae were exposed to either a seriesof seawater salinities from 5-40 in 5 increments or of 10-40in 10 increments for one hour during each day of their development.The osmoconcentrations of 20-80 nanoliter hemolymph samplesfrom each of four larvae were measured separately by determinationsof freezing point depression. Eyestalkless larvae in metecdysis of zoeal Stage II were exposedto the same osmoconcentrations as unoperated controls to testfor osmoregulation by eyestalk nerve tissue. Larvae tend to be isosmotic with seawater of 30-40 salinity(S) and to hyperregulate in more dilute media except for larvaein their first diecdysis which remain isosmotic. Larvae in thelast few hours of proecdysis hyperregulate against 40 S as well,presumably to insure inflow of water to establish a greaterbody volume during hardening of the exoskeleton. They are consequentlyisosmotic in the very early metecdysis. The presence of eyestalks at the first metecdysis (Stage II)keeps zoeas hyperosmotic to 5-30 S, but prevents them from hyperregulationagainst 40 S. Eyestalkless zoeas become isosmotic with 5-30S and hyperregulate against 40 S like late proecdysal larvae.Lack of eyestalks makes diecdysal animals hyperregulate againsta medium with which normal animals are isosmotic. The eyestalkinfluence affects second metecdysal (Stage III) larvae in away similar to those in first metecdysis except that it apparentlyalso prevents a curious tendency to hyporegulate in 5-30 S.Similarly, in this stage, the eyestalks prevent hyperosmosityin 40 S seawater as they do during the first day of zoeal StageII. Eyestalk nerve tissue reduces the degree to which diecdysallarvae of this stage remain hyperosmotic to media of 10 S and20 S and apparently causes larvae to be hypoosmotic at 40 S. Preliminary data indicate that removal of eyestalks has littleeffect on proecdysal larval osmoregulation or on regulationof Stage IV zoeas. In other experiments ablation of eyestalks caused Stage II larvaeto lose the ability to osmoregulate against 10-30 S seawaterwithin two hours after the operation. The same zoeas did nothyperregulate against 40 seawater until four hours after removalof eyestalks.     

Acute toxicity of ammonia on Litopenaeus vannamei Boone juveniles at different salinity levels

Litopenaeus vannamei juveniles (total length 22+/-2.4 mm) were exposed to different concentrations of ammonia-N (un-ionized plus ionized ammonia as nitrogen), using the static renewal method at different salinity levels of 15 per thousand, 25 per thousand and 35 per thousand at pH 8.05 and 23 degrees C. The 24, 48, 72, 96 h LC50 values of ammonia-N on L. vannamei juveniles were 59.72, 40.58, 32.15, 24.39 mg l(-1) at 15 per thousand; 66.38, 48.83, 43.17, 35.4 mg l(-1) at 25 per thousand; 68.75, 53.84, 44.93, 39.54 mg l(-1) at 35 per thousand, respectively. The 24, 48, 72, 96 h LC50 values of NH(3)-N (un-ionized ammonia as nitrogen) were 2.95, 2.00, 1.59, 1.20 mg l(-1) at 15 per thousand; 2.93, 2.16, 1.91, 1.57 mg l(-1) at 25 per thousand; 2.78, 2.18, 1.82, 1.60 mg l(-1) at 35 per thousand, respectively. As the salinity decreased from 35 per thousand to 15 per thousand, susceptibility of ammonia-N increased by 115%, 132%, 140% and 162% after 24, 48, 72 and 96 h exposure, respectively. The "safety level" for rearing L. vannamei juveniles was estimated to be 2.44, 3.55, 3.95 mg l(-1) for ammonia-N and 0.12, 0.16, 0.16 mg l(-1) for NH(3)-N in 15 per thousand, 25 per thousand and 35 per thousand, respectively.     

Influence of salinity and cadmium on the survival and osmoregulation of Callianassa kraussi and Chiromantes eulimene (Crustacea: Decapoda)

This study investigated the influence of salinity and cadmium on the survival and osmoregulatory capability of two decapod crustaceans, Callianassa kraussi and Chiromantes eulimene. Callianassa kraussi was able to survive in salinities of 5–55 over 96 h, whilst C. eulimene survived in 0–55 over the same time period. The 96-hour cadmium LC₅₀ for both species decreased progressively at salinities above and below their respective isosmotic conditions, with the decrease being slightly more pronounced below compared to above isosmotic salinity. A hypo-iso-osmoregulatory strategy was followed by C. kraussi as it hyper-osmoregulated at salinities between 5 and 25 and osmoconformed at salinities greater than 25. Chiromantes eulimene followed a hyper-hypo-osmoregulatory strategy; it hyper-regulated in salinities from 0 up to isosmotic conditions at about 28 (c. 780 mOsm kg^?1), followed by hypo-regulation up to 55. The effect of cadmium exposure on the osmoregulatory capacity of C. kraussi was more pronounced at hyper-regulating salinities (5–25) whilst on C. eulimene the influence was more pronounced at salinities above the isosmotic point (28). The influence of salinity and cadmium on both survival and osmoregulation of the two crustaceans are discussed by outlining the chemical and physiological mechanisms involved.     

Study of perkinsosis in the carpet shell clam Tapes decussatus in Galicia (NW Spain). I. Identification of the aetiological agent and in vitro modulation of zoosporulation by temperature and salinity

Morphological characters of zoosporulation stages and DNA sequence of the internal transcribed spacer (ITS) region and the small subunit ribosomal RNA (SSU rRNA) gene confirmed that the aetiological agent of perkinsosis in the clam Tapes decussatus from Galicia (NW Spain) was Perkinsus atlanticus Azevedo, 1989. In vitro modulation by temperature and salinity of the zoosporulation of the parasite was studied. The optimum temperature range for zoosporulation was 19 to 28 degrees C. The temperature range allowing zoosporulation in vitro was 15 to 32 degrees C, which is broader than previously reported (24 to 28 degrees C) for P. atlanticus, and strongly suggests that zoospores can be produced in Galician Rias, where temperature ranges from 10 to 22 degrees C. Prezoosporangia held at 10 degrees C for 2 mo (similar to winter conditions in Galician waters) gave rise to viable zoospores after they were transferred to higher temperatures. This suggests that prezoosporangia could overwinter and zoosporulate in the next spring. Zoospores could survive for up to 22 and 14 d at 28 and 10 degrees C, respectively. The optimum salinity range for zooporulation was 25 to 35 per thousand. Zoospore production was abruptly reduced as salinity decreased. The lowest salinity at which zoosporulation was observed was 10 per thousand. The effectiveness of different chlorine concentrations and exposure lengths to kill prezoosporangia and zoospores was tested. No survival of free zoospores, free prezoosporangia and prezoosporangia included in gill tissue was observed after incubation for 1 h with 50, 200 and 3,000 ppm of chlorine, respectively.     

Effect of salinity on the osmotic,chloride, total protein and calcium concentrations in the hemolymph of the prawn Peneaus monodon (fabricius)

• 1.1. Osmolality and chloride concentrations in the hemolymph of Penaeus monodon became stable 1 day after molting in 32 ppt, while total protein and calcium concentrations remained stable throughout the molting cycle. When intermolt (≥ 36 hr postmolt) animals were transferred from control (32 ppt) to experimental (8–40 ppt) salinities, osmolality, chloride and total protein, but not calcium, concentrations in the hemolymph achieved steady state values 24–48 hr after transfer.
• 2.2. The hemolymph osmolality was a linear function (slope = 0.28) of medium osmolality at salinities between 8 and 40 ppt. It was isosmotic to seawater at 698 mOsm (10 g prawns) and 752 mOsm (30 g), and was hyperosmotic to the medium below isosmotic concentrations, and hypoosmotic to those above.
• 3.3. Hemolymph chloride concentration was isoionic to seawater at 334 mM, and was hyperregulated below isoionic concentrations, and hyporegulated to those above.
• 4.4. P. monodon maintained its hemolymph calcium concentration between 6.4 and 10 mM when medium salinities increased from 8 to 40 ppt.
• 5.5. Total protein concentration in the hemolymph was independent of medium salinity (8–40 ppt) and hemolymph osmolality (540–850 mOsm).

     

Influence of salinity and temperature on growth and survival of the planktonic larvae of Marenzelleria viridis (Polychaeta, Spionidae)

In a series of experiments, the planktonic larvae of Marenzelleriaviridis (Verrill, 1873) were exposed to various combinationsof salinity (S = 0.6, 2.5, 5.0, 10 and 20) and temperature (T= 5, 10 and 20C) from the 1-setiger stage to the onset of metamorphosis(16- to 17-setiger stage). One-setiger larvae were unable tocomplete their development to metamorphosis at salinities below5. Metamorphosis was successful at salinities of 10 and 20,when the animals adopted a benthic life mode. Larval developmentwas more rapid at 10 than at 20, and was positively affectedby higher temperatures. Larvae exposed to a salinity of 3.5at the 4- to 5-setiger stage developed and completed metamorphosisto benthic juveniles despite the low salinity. These larvaedeveloped most rapidly at a temperature of 10C. The salinitytolerances (LC₅₀) of M. viridis larvae (t = 48 h), juvenilesand adults (t = 72 h in each case) were determined at 10C.The results showed that all development stages can toleratesalmities <1 The importance of constraints on developmentand tolerance to low salinities for the successful colonizationof oligohaline regions is shown and discussed in connectionwith other brackish-water organisms.     

Effects of temperature and salinity fluctuation on the ammonium excretion and osmoregulation of juveniles of Penaeus vannamei,Boone

This study assesses the effect of temperature and fluctuations in salinity on the nitrogen excretion and osmoregulation of Penaeus vannamei juveniles to determine the lowest stress combination so that these can be used to optimize production of the Mexican strain in culture. The ammonium excretion rate of juveniles acclimated to 20, 24, 28 and 32°C was measured. Fluctuating salinity levels were applied to these animals in a sequence of 40%o, 33, 25, 18, 11, 18, 25, 33 and back to 40%o. The results indicate that when the salinity was reduced from 40 to 11%> the ammonium excretion of the shrimp was reduced. The osmotic concentration of the animals was hyposmotic as the salinity decreased from 40 to 25%o, hyperosmotic during the 18–11–18 in %> interval and hyposmotic as the salinity increased from 25 to 40%> again. The range of isomotic points over this range of salinity was 712–777mmol Kg^‐1. The ammonium excretion of P. vannamei exposed to these experimental conditions can be attributed to the process of osmoregulation because excretion was increased when the shrimp were hyper‐regulating and reduced when they were hypo‐regulating. Based on our results, the animals experience the lowest stress in a temperature between 27 to 30°C and a salinity close to the isosmotic point between 25 ‐ 27%o. We propose that this should prove to be the optimal temperature and salinity regime for culturing the Mexican strain of P. vannamei.     

Effects of water temperature and salinity on elimination of Salmonella charity and Escherichia coli from Sydney rock oysters (Crassostrea commercialis)

The elimination of Salmonella charity and Escherichia coli from the Sydney rock oyster, Crassostrea commercialis, was examined during commercial purification of oysters under different water temperatures and salinities. Both organisms were rapidly eliminated at 18 to 22 degrees C. Purification was effective but slower at 24 to 27 degrees C and incomplete and inconsistent at temperatures below 17 degrees C. The oysters suffered stress and were not effectively purified at water salinities of 15 to 20% but were rapidly purified at 32 to 47% salinity. Winter-harvested and summer-harvested oysters were purified similarly in water at 18 to 22 degrees C and 32 to 36% salinity.     

Effects of water temperature and salinity on elimination of Salmonella charity and Escherichia coli from Sydney rock oysters (Crassostrea commercialis).

The elimination of Salmonella charity and Escherichia coli from the Sydney rock oyster, Crassostrea commercialis, was examined during commercial purification of oysters under different water temperatures and salinities. Both organisms were rapidly eliminated at 18 to 22 degrees C. Purification was effective but slower at 24 to 27 degrees C and incomplete and inconsistent at temperatures below 17 degrees C. The oysters suffered stress and were not effectively purified at water salinities of 15 to 20% but were rapidly purified at 32 to 47% salinity. Winter-harvested and summer-harvested oysters were purified similarly in water at 18 to 22 degrees C and 32 to 36% salinity.     

Bacterial diversity of a cyanobacterial mat degrading petroleum compounds at elevated salinities and temperatures

Cyanobacterial mats of the Arabian Gulf coast of Saudi Arabia experience extreme conditions of temperature and salinity. Because they are exposed to continuous oil pollution, they form ideal models for biodegradation under extreme conditions. We investigated the bacterial diversity of these mats using denaturing gradient gel electrophoresis and 16S rRNA cloning, and tested their potential to degrade petroleum compounds at various salinities (fresh water to 16%) and temperatures (5 to 50 degrees C). Cloning revealed that c. 15% of the obtained sequences were related to unknown, possibly novel bacteria. Bacteria belonging to Beta-, Gamma- and Deltaproteobacteria, Cytophaga-Flavobacterium-Bacteroides group and Spirochetes, were detected. The biodegradation of petroleum compounds at different salinities by mat microorganisms showed that pristine and n-octadecane were optimally degraded at salinities between 5 and 12% (weight per volume NaCl) whereas the optimum degradation of phenanthrene and dibenzothiophene was at 3.5% salinity. The latter compounds were also degradable at 8% salinity. The same compounds were degraded at temperatures between 15 and 40 degrees C but not at 5 and 50 degrees C. The optimum temperature of degradation was 28-40 degrees C for both aliphatics and aromatics. We conclude that the studied microbial mats from Saudi Arabia are rich in novel halotolerant and thermotolerant microorganisms with the potential to degrade petroleum compounds at elevated salinities and temperatures.     

Drinking and osmoregulation in the mangrove crab Ucides cordatus following exposure to benzene

In benzene-exposed Ucides cordatus acclimated for 96 h to 9 and 34 per thousand SW, haemolymph, urine and gastric juice are isosmotic with each other, but differ significantly in osmolality from external media. In both salinities, under benzene action, urine K+ excretion and calcium absorption are increased significantly, whereas Na+ absorption and Mg2+ excretion show U/B ratios similar to control values. In 9 per thousand SW, some ionic exchanges via benzene-exposed gills are possibly hastened. Benzene exposure decreases significantly branchial chamber water osmolality, [Na+] and [K+], whereas [Ca2+] and [Mg2+] are unaffected. However, faster medium exchange presumably occurs in 34 per thousand SW, both crab groups show branchial chamber water osmotic and ionic concentrations similar to surrounding medium. Benzene exposure unaffected gastric juice composition. In both media, [Ca2+] and [Mg2] accumulate several times higher than surrounding media, and [Na+] and [K+] are significantly hypo-ionic to haemolymph. Na+ and K+ G/H ratios are lower in crabs acclimated to 34 per thousand SW than in crabs acclimated to 9 per thousand SW. Drinking rates are enhanced by benzene exposure and are higher at 34 per thousand SW than in seawater isosmotic with the haemolymph (26 per thousand SW). Benzene exposure affects significantly osmoregulatory capability, slowing haemolymph dilution after transfer to clean 9 per thousand SW. Lower haemolymph dilution rate accounts for higher osmolality, but 48 h after transfer there is no recovery like in control crabs. Haemolymph transfusion experiments suggest an interaction among effects of benzene and hormonal factors, possibly on water influx.