Contrasts in the hypo-osmoregulatory abilities of a freshwater and an anadromous population of inconnu

Juvenile freshwater and anadromous inconnu Stenodus leucichthys regulated plasma ions following a direct transfer from fresh to brackish water (10–15‰), but suffered osmoregulatory collapse with 100% mortality in 48 h when directly transferred to 25‰ salinity. Acclimation to brackish water for 2 weeks improved hypo-osmoregulatory capacity in both populations, with acclimated fish showing smaller increases in blood plasma ion concentrations, higher Na⁺-K⁺ ATPase activity, and lower mortality than non-acclimated fish following transfer to 25‰ sea water. Anadromous inconnu maintained pre-treatment plasma ion levels during acclimation, whereas these levels increased during acclimation in freshwater inconnu. Juvenile anadromous inconnu are therefore able to adapt physiologically to sea water of at least 25‰, if brackish-water acclimation is available, but freshwater inconnu have diminished saltwater tolerance, relative to the anadromous form.     

Adaptation of rainbow trout (Salmo gairdnerii) to sea water: Changes in calcitonin levels

• 1.1. The calcitonin content of the ultimobranchial body (UBB) and plasma levels of calcitonin, calcium and phosphate were measured in rainbow trout (Salmo gairdnerii) following their transfer from fresh to sea water.
• 2.2. The plasma calcium level remained unchanged throughout the experiment while the UBB calcitonin content, plasma calcitonin and plasma phosphate rose significantly during the hours immediately following transfer.
• 3.3. The levels of all three subsequently fall so that, 8–15 days later, a new equilibrium was established with lower than control (fresh water) levels of UBB calcitonin, plasma calcitonin and plasma phosphate.
• 4.4. It would appear, from these data, that calcitonin plays some part in the endocrine regulation of sea water transfer.

     

Effects of salinity on the ionic balance and growth of juvenile turbot

The effects of salinity changes (27, 19 and 10‰) on seawater-adapted juvenile turbot were studied on their plasma osmolarity and ion concentrations, on oxygen consumption, on gill Na⁺,K⁺-ATPase activity after 3 months and on growth parameters. All plasma concentrations (except chloride) were unchanged, suggesting that fish were well adapted to their environment. Oxygen consumption was significantly decreased in the 19 and 10‰ groups, where fish weighed significantly more 105 days after transfer than fish maintained in sea water. These results, and the fact that apparent food conversion rates were lower in a diluted environment, suggest that on a long term schedule growth conditions could be improved by adaptation to brackish waters (salinities between 10 and 19‰). The effects of transfer from sea water to 27, 19, 10 and 5‰ were also followed during the first 3 weeks. With salinity 10‰ a steady state was reached on day 21 with all plasma values within the same range. The significant differences observed in osmolarity, plasma ion concentrations and Na⁺,K⁺-ATPase activity 3 weeks after transfer of juveniles to 5‰ salinity, compared with transfers in higher salinities, suggest that there is a threshold of acclimation of turbot to a hypotonic environment.     

The effects of hypophysectomy, prolactin therapy and environmental calcium on electrolyte balance of the brown trout Salmo trutta, L.

Adaptation of the brown trout to fresh water containing increasing concentrations of calcium resulted in a decrease in plasma electrolyte level and total electrolyte excretion. The electrolyte excretion rate was higher at the beginning than at the end of the urine collection periods. Hypophysectomized fish had a lower plasma electrolyte concentration than the controls. This deficiency was partially corrected by polactin therapy. High environmental calcium was only effective to a limited extent. There was no difference in the normal renal sodium output between hypophysectomized and intact fish in fresh water. Environmental calcium did not have any significant effect on renal electrolyte output of hypophysectomized fish.     

盐度对秋茄凋落叶分解过程中物质与能量动态的影响

在室内人工模拟潮汐, 研究了4种盐度(0、10‰、25‰和35‰, 分别代表淡水、低盐、中盐和高盐)下秋茄(Kandelia candel)凋落叶分解过程中物质与能量动态的差异。结果表明, 高盐处理下的失重率和平均分解速率显著低于淡水和低盐处理, 而高盐下的半分解理论值则高于其他处理; 盐度对分解过程中的残叶氮磷变化动态有显著影响, 其中, 残叶氮的释放速率在实验后期会随着盐度的升高而上升, 高盐度下残叶总氮含量显著低于低盐或淡水处理; 而在分解第1周, 淡水或低盐处理能加速磷的释放, 但中高盐度残叶中总磷含量最终会低于淡水和低盐处理; 盐度同样能对残叶热值产生显著影响, 淡水和低盐处理下的碎屑热值要显著高于高盐处理下的残叶热值, 但不同盐度下分解的能量损失差异不显著。     

Salinity relationships in a freshwater population of eastern mosquitofish

Tolerance limit to elevated ambient salinity, and plasma osmotic regulatory capabilities were evaluated in a freshwater population of Gambusia holbrooki. The upper tolerance limit of ambient salinity was found to be 25‰. Plasma osmotic concentrations trended sharply upward with increasing salinity, but in a stepwise fashion, unlike patterns in related, but more euryhaline species. These laboratory observations are consistent with field observations that natural populations of G holbrooki are generally restricted to fresh and dilute brackish waters.     

Euryhaline adaptations in the fat sleeper, Dormitator maculatus

Salinity tolerances and plasma osmotic concentrations were determined in the fat sleeper, Dormitator maculatus , a common species in estuarine and coastal fresh waters along the Atlantic and Caribbean coasts of North, Central and South America. Analyses followed sequential laboratory acclimations to a series of ambient salinities at a constant temperature of 20 ± 1° C and photoperiod of 12L: 12D. These fish tolerated a range of ambient salinities from fresh water through a salinity of 75‰. Plasma osmotic concentrations were regulated at an essentially constant level in the salinity range from fresh water through a salinity of 50‰, beyond which plasma concentrations trended upward with increased ambient salinity. We conclude that D. maculatus , while truly euryhaline, docs not show the extreme euryhalme capabilities of several teleost fishes that are 'full-time' estuarine inhabitants.     

Salinity tolerance of freshwater acclimated, small-sized Arctic charr, Salvelinus alpinus from northern Labrador

Arctic charr, Salvelinus alpinus , less than 150 mm in size were frequently captured at sea in northern Labrador in areas where salinities of 30‰ or higher had been recorded. These captures were inconsistent with many earlier reports for other areas that indicated Arctic charr less than 150 mm in size were not found at sea. A series of salinity challenge tests was carried out in the field, using wild Ikarut River charr, and in the laboratory, using cultured Fraser River charr, to understand more about the potential fate of these small fish. The results of challenge tests with small Arctic charr (< 120 mm) indicated that at intermediate salinities (10–20‰), these fish can readily survive. In laboratory tests with salinities at 30‰, survival was size dependent and would suggest that in natural situations, small charr would require periodic access to fresh or brackish water to stay alive. The influence of water temperature on salinity tolerance may be important when fish are exposed to temperatures that are below 0° C.     

Plasma homeostasis and cloacal urine composition inCrocodylus porosus caught along a salinity gradient

Summary Juveniles of the Estuarine or Saltwater Crocodile,Crocodylus porosus, maintain both osmotic pressure and plasma electrolyte homeostasis along a salinity gradient from fresh water to the sea. In fresh water (FW) the cloacal urine is a clear solution rich in ammonium and bicarbonate and containing small amounts of white precipitated solids with high concentrations of calcium and magnesium. In salt water (SW) the cloacal urine has a much higher proportion of solids, cream rather than white in colour, which are the major route for excretion of potassium in addition to calcium and magnesium. Neither liquid nor solid fractions of the cloacal urine represent a major route for excretion of sodium chloride. The solids are urates and uric acid, and their production probably constitutes an important strategy for water conservation byC. porosus in SW. These data, coupled with natural history observations and the recent identification of lingual salt glands, contribute to the conclusion thatC. porosus is able to live and breed in either fresh or salt water and may be as euryhaline as any reptile.     

The effects of salinity and temperature on the development and survival of fish parasites

In brackish water the variety of marine and freshwater parasite species is considerably reduced. The distribution in brackish water of most marine endoparasites is restricted by the salinity tolerance of their hosts, most of the parasite species are more tolerant than their hosts. The influence of salinity and temperature on nine species has been examined; first stage larvae of Contracaecum aduncum develop in 0-32‰ salinity; Cryptocotyle lingua proved to be infective at salinities down to 4‰. The greatest resistance was found in Anisakis larvae from herring Clupea harengus , which survived for more than half a year. Parasites in the fish intestines appear to be unaffected by changing water salinities, as the osmolarity in the intestines stays nearly constant. Marine ectoparasites ( Acanthochondria depressa, Lepeophtheirus pectoralis ) survive about three times longer than freshwater species ( Piscicola geometra, Argulus foliaceus ) when salinity is 16‰. High temperature increases the effects of adverse salinities on parasites. There is evidence that none of these ecto-parasitic species can develop within the range of 7-20‰ salinity.     

Evidence of prezygotic isolation,but not assortative mating,between locally adapted populations of Fundulus heteroclitus across a salinity gradient

Selection along environmental gradients can drive reproductive isolation and speciation. Among fishes, salinity is a major factor limiting species distributions, and despite its importance in generating species diversity, speciation events between marine and freshwater are rare. Here, we tested for mechanisms of reproductive isolation between locally adapted freshwater and brackish water-native populations of killifish, Fundulus heteroclitus, from either side of a hybrid zone along a salinity gradient. There was evidence for pre-zygotic endogenous reproductive isolation with reduced fertilization success between crosses of freshwater-native males and brackish water-native females. Exogenous pre-zygotic isolation was also present where females had highest fertilization in their native salinity. We used a replicated mass spawning design to test for mate choice in both brackish and fresh water. After genotyping 187 parents and 2523 offspring at 2347 SNPs across the genome, 85% of offspring were successfully assign to their parents. However, no reinforcing mate choice was observed. These results therefore demonstrate emerging, yet limited, reproductive isolation and incipient speciation across a marine to freshwater salinity gradient and suggest that both endogenous and exogenous mechanisms, but not assortative mating, contribute to divergence.     

Eco-physiology of Palaemonetes antennarius (Crustacea, Decapoda): the influence of temperature and salinity on cardiac frequency

Abstract.  The effect of different temperatures and salinities on the cardiac frequency of the freshwater shrimp Palaemonetes antennarius is investigated. The results show that both temperature and salinity influence heart rate. Variations in water temperature are associated with changes in heart rate: variations higher than 8°C in 6 h affect not only heart rate, but also shrimp survival. After an initial rapid increase, the heart rate returns to initial values at saline concentrations of 15‰ and 30‰, whereas, at 20‰ salinity, the shrimps show a persistent decrease of heart rate throughout the test. The marked tolerance of variations of temperature and salinity suggests that P.   antennarius is well adapted to waters with large salinity and temperature oscillations. Cardiac frequency can be used as a valid indicator of physiological stress in this species.     

Salinity tolerance of young catfish, Clarias lazera (Burchell)

Experiments were conducted to determine the adaptability of young catfish, Claria lazera , to various saline concentrations. Young catfish, total length 52–88 mm, were subjected to abrupt and gradual changes from fresh water (salinity = 0.14‰) to various salinities. Ninetyfour per cent survival occurred when the fish were transferred from fresh water to 25% sea water (salinity = 9.5‰ No fish survived higher salinities even through gradual change.     

Apparent anion imbalance in the fresh water adapted eel

Summary On adapting brackish waterAnguilla anguilla to fresh water it was noted that, while the plasma sodium, magnesium,pCO₂ and pH were held reasonably constant, there was a substantial fall in chloride concentration (–33 mEq). The gradient of the linear correlations between plasma sodium and chloride also fell (brackish water gradient=0.92, fresh water gradient=0.21) indicating that a new pattern of plasma ion interrelationships was being established. Comparison with plasma Na/Cl ion ratios from other fishes suggested that this phenomenon was peculiar toA. anguilla. Corresponding with the very low plasma chloride levels plasma bicarbonate was four to five times that found in other fishes, and this was thought related to the finding that the haematocrit value almost doubled during adaptation to fresh water. In fresh water adapted fish a fall in plasma chloride was associated with a rise in plasma bicarbonate, however the charge compensation effect of this response was only partial as summing the common plasma cations and anions left an anion deficit of about 34 mEq to be accounted for.     

Effects of sodium and magnesium sulfate in drinking water on mallard ducklings

One-day-old mallard (Anas platyrhynchos) ducklings were given drinking water for up to 28 days that contained concentrations of sodium and/or magnesium similar to those found in saline wetlands. Growth, tissue development, and biochemical characteristics of these ducklings were compared to those reared on fresh water. Much of the ingested salt was excreted by passage of voluminous fluid excreta. This effect occurred in birds given water with as little as 500 ppm Mg or 1,000 ppm Na. The supraorbital salt gland was active within 4 days in ducklings drinking water containing greater than or equal to 1,500 ppm of Na. Feather growth was decreased in ducklings drinking water with greater than or equal to 1,500 ppm of either Na or Mg. Ducklings drinking water with 3,000 ppm of either ion, or 1,500 ppm of each, grew more slowly than control birds. Ducklings drinking water with 3,000 ppm of either Na or Mg had reduced thymus size and bone breaking strength. Those drinking water with 3,000 ppm of Mg, or 3,100 ppm Na and 1,300 ppm Mg also had less trabecular bone and enlarged adrenals. Birds drinking the latter water had an elevated concentration of Na and calcium, and a decreased concentration of phosphorus and chloride in their serum, and elevated plasma protein levels. Ducklings reared on fresh or slightly saline water adapted very poorly to an abrupt change to more saline water (specific conductivity = 15,250 microns hos/cm) at 14 days of age. These birds stopped eating, became inactive and some died within 3 days; survivors had many tissue and biochemical abnormalities at 20 days of age. The level of salinity in these trials was similar to that in "brackish" or "moderately saline" wetlands and lower than that previously found to have effects on growth and feathering of ducklings. Many of the sublethal effects were subtle and non-specific manifestations of stress, and would be difficult to detect in wild ducklings on saline wetlands.     

Salinity tolerance of laboratory-reared larvae of the California killifish, Fundulus parvipinnis Girard

Newly hatched larvae of the California killifish ( Fundulus parvipinnis ) reared in the laboratory, were tolerant of salinities from fresh water to 70‰. Their salinity tolerance was influenced by incubation salinity; larvae hatched in lower incubation salinities exhibited greater freshwater tolerance than those hatched in higher salinities. In gradual acclimation tests, the upper median lethal salinity for the larvae was 130‰. Freshwater tolerance of the larvae decreased with age; yolk sac larvae were completely tolerant of fresh water while larvae more than 15 days old were least resistant.     

Influence of some environmental variables on the ascorbic acid status of mullet, Mugil cephalus L., tissues. I. Effect of salinity, capture-stress, and temperature

The effects of capture stress, exposure to a hypo-osmotic environment and elevated water temperatures on the ascorbic acid (AsA) content of several mullet, Mugil cephalus , tissues were examined. All the treatments significantly altered tissue AsA levels, but the pattern of AsA fluctuations varied. Gill AsA concentrations increased two fold after exposure to a hypo-osmotic medium (salinity changed from 30‰ to 5‰), whereas AsA content in this tissue declined after capture. Both treatments depleted AsA reserves in the kidney. AsA concentrations in the brain increased after exposure to low salinity and elevated water temperatures, but were unaffected by capture stress. None of the treatments caused long term alteration of hepatic AsA reserves. Ascorbic acid inhibited oubain-sensitive Na⁺, K⁺-ATPase activity of gill tissue in vitro . The results suggest an involvement of AsA in osmo- or ion-regulatory functions of teleosts gills, salinity and thermal adaptation mechanisms in neural tissue, and the response of renal tissue to adverse environmental stimuli.     

Haematological effects of stress on a teleost, Esox lucius L.

Stress produces a haemoconcentration, elevated blood lactate, increased glucose concentrations and alters the plasma electrolyte balance in two groups (brackish- and freshwater) of the northern pike, Esox leucius L., after one month's starvation. A method for dorsal aorta catheterization and a receptacle for cannulating fish is described.
The blood glucose level of the freshwater pike was twice that of the brackish-water group, and the plasma sodium and magnesium concentrations in the brackish-water pike were significantly higher. The haematocrit, haemoglobin and blood lactic acid concentrations were higher in freshwater pike. The plasma potassium and calcium concentrations in the two groups did not differ.
Haemoconcentration due to stress by handling for 1.5 min was shown by changes in haematocrit and haemoglobin values. The haemoglobin concentration returned to normal in freshwater pike after 4 h but in brackish-water pike after 12 h.
As a result of handling, the blood lactic acid level rose steeply and required 12 h to return to normal.
The blood glucose concentration rose to its maximum value within 1 h of handling and required two days to return to normal.
The plasma sodium level remained stable after handling, but the potassium level was erratic. In brackish-water, the potassium concentration of the pike remained high for 12 h after stress, but in the freshwater group, after a rise, the concentration fell to below the initial level within 4 h. The changes of the potassium concentrations in relation to sampling time are discussed. The changes in the divalent ion concentrations were marked and similar in the two groups; with an increase lasting 1–4 h and then a fall below the initial level, which was regained after two days.     

Salinity Tolerance of Some Teleost Fishes of Peter the Great Bay, Sea of Japan

Salinity tolerance in some marine teleost fishes was studied. Based on a comparison of sexually mature specimens in the summer season, the investigated species can be arranged in the order of decreasing capability for hyperosmoregulation into the following series: the Far Eastern dace Trybolodon brandti, the haarder Mugil soiuy > the frog sculpin Myoxocephalus stelleri > the snowy sculpin M. brandti > the plain sculpin M. jaok > the masked greenling Hexagrammos octogrammus > the pipefish Syngnathus acusimilis. The adult Far Eastern dace and the haarder showed high salinity tolerance and fully adapted to fresh water. Sculpins and the masked greenling usually occur only in seas or brackish water, but they were capable of enduring fresh water for a long time. Unlike them, the pipefish, which is also a euryhaline fish and occurs in river estuaries and brackish bays, perished in fresh water within 1 h. Representatives of the genus Myoxocephalus show between-species differences in salinity tolerance, which allows them to colonize extensive near-shore areas of the sea and to occupy specific ecological niches.     

Adaptive capacity of larvae of the haarder Liza haematocheila (Mugilidae, Mugiliformes) under decreasing salinity of the environment

The response of early juveniles of the haarder Liza haematocheila (= Mugil soiuy) to changes of water salinity, and the growth and survival of larvae in water of different levels of salinity were studied. The capacity of adaptation of the larvae of the haarder to fresh water is manifested at early ages. Normally developing six-day-old larvae of the haarder easily endure the transfer from seawater (17–19‰) to brackish water (5‰) and a day later, to fresh water. The resistance of larvae to abrupt decreases in salinity increases with age. Directly transferred to fresh water, all 6–12-day old larvae perish, compared to only 8–30% of 2–3-week old larvae (those retarded in growth). In the course of raising, the larvae have tended to survive better in brackish water (5‰). At decreasing salinity, the growth rate, the content of defatted dry matter, and the content of lipids increase. In fresh water, the stock lipids (triacylglycerols) are accumulated more intensively. With consideration of the original and published data, the problem of formation of the osmoregulatory system in the ontogenesis of mugilids is discussed.