Drinking Sea Water Research Articles

Drinking behaviors and water balance in marine vertebrates

Acquisition of fresh water is important to animals, and is both difficult and critical for species residing in marine environments. Adaptive radiations to fully marine habitats were constrained by the need for fresh water and the capacity of various taxa to adapt physiology to reliance on sources of water other than free drinking water. Here, we review the water relations of marine vertebrates, with an emphasis on drinking and the need to procure fresh water. Numerous marine teleost fishes drink seawater, but some do not, and drinking is more variable and complex than suggested by textbooks. The mechanisms by which fishes and other vertebrates regulate water balance involve the renin–angiotensin and aldosterone endocrine systems, but plasma osmotic and ionic concentrations as well as other chemical signals can also be involved. Multiple mechanisms for stimulation of drinking are operative and diverse among species. Clearly, evolutionary adaptations to environmental salinities can alter drinking behaviors. Marine elasmobranchs do not characteristically drink seawater, but euryhaline species drink upon returning to more concentrated seawater, as with teleosts. Hagfish are osmoconformers, and there is no evidence for drinking. In general, marine reptiles and most marine mammals and seabirds do not drink seawater. Exceptions include sea turtles, cetaceans, and some pinnipeds. Some marine species (e.g., sea snakes) require fresh water that can be acquired from ephemeral rainwater lenses, while others are adapted to utilize dietary and metabolic water. Regardless of drinking behaviors, numerous forms have evolved varied strategies for conserving water while reducing its losses to the surrounding sea.

The Lifeboat

Charlotte Rogan's The Lifeboat is an interesting oceanic story about an accident at sea, the grim time survivors spend aboard a lifeboat, and the legal aftermath for newlywed Grace Winters (Winters), 22, who loses her husband in the wreck. The most compelling element of the novel, aside from its tale of survival and mutiny on the sea, is the series of legal complications and issues which centers the book.The Lifeboat also bears almost the same title as a 1944 Alfred Hitchcock movie for which John Steinbeck wrote the story treatment (Lifeboat). Steinbeck was unhappy with the film and asked that his name to be removed from the credits, but ironically was nominated for an Oscar for his efforts (although Hitchcock also did bring in other writers to adapt and change the story for the big screen). Both Rogan's novel and Steinbeck's screenplay have produced memorable oceanic stories which, though rooted in history, tell universal stories. Sadly, the new book is more of a legal thriller than a successful statement of the human condition. Told mostly in flashbacks, Rogan's book is an effective story about personal development. Winters, who must fend for herself among strangers and the elements without her husband Henry, learns profound lessons about society, survival, and the law. This tale is more elaborate than Steinbeck's screen treatment for the Hitchcock movie Lifeboat.After a shipwreck caused by an explosion in 1914, Winters is cast on the sea among strangers on a lifeboat which has too many people aboard and weighs down heavily in the water. These people do not have sufficient provisions for a long period on the sea. Therefore, they need to get rid of some on the boat, and they find it is necessary to prevent some survivors of the wreck from getting into the boat. Winters is a survivor and adapts to her predicament, which results in her being included along with some of the crew mates who must face being put on trial for their actions aboard the ship. There is mutiny and murder among the crew who struggle to survive. They also fight among themselves to stay out of the water. The ocean is portrayed as a grim wilderness, and the characters must persevere. They do not find as much fish as they would like to eat, and it is not safe to drink sea water. Unlike the shipwreck survivors in the Hitchcock film, these survivors do not need an enemy combatant on the ship.The writing about the sea is not very spectacular, but Rogan makes it clear that the vacation for the crew is over, especially for Winters who is now without a spouse: “Now, however, I knew he was in the sea, lurking there, hand in hand with Hardie, rising up in these big waves and splashing down random pieces of himself in our boat” (253). The structure of the book detracts from a full appreciation of the story, leaving readers waiting for answers to major questions. The book, however, is compelling, as are the plot elements for which readers await resolution. Winters learns some practical, but debatable lessons from the experience: “I replied that … perhaps there was a more profound point to be made about innocence, that perhaps a person could not be both alive and innocent.” (237). While the court case is clearly presented, it is not resolved until close to the novel's end. Winters emerges as a survivor of the harsh sea, the grim and sometimes dangerous crew mates, personal loss, and an intrusive legal system. While the book does become a page-turner, it does not update Steinbeck's story. Also, it lacks the seriousness of Steinbeck's work, which can be seen as a parable of the human condition. Nevertheless, it is a more contemporary treatment.

Euryhaline pufferfish NBCe1 differs from nonmarine species NBCe1 physiology

Marine fish drink seawater and eliminate excess salt by active salt transport across gill and gut epithelia. Euryhaline pufferfish (Takifugu obscurus, mefugu) forms a CaCO(3) precipitate on the luminal gut surface after transitioning to seawater. NBCe1 (Slc4a4) at the basolateral membrane of intestinal epithelial cell plays a major role in transepithelial intestinal HCO(3)(-) secretion and is critical for mefugu acclimation to seawater. We assayed fugu-NBCe1 (fNBCe1) activity in the Xenopus oocyte expression system. Similar to NBCe1 found in other species, fNBCe1 is an electrogenic Na(+)/HCO(3)(-) cotransporter and sensitive to the stilbene inhibitor DIDS. However, our experiments revealed several unique and distinguishable fNBCe1 transport characteristics not found in mammalian or other teleost NBCe1-orthologs: electrogenic Li(+)/nHCO(3)(-) cotransport; HCO(3)(-) independent, DIDS-insensitive transport; and increased basal intracellular Na(+) accumulation. fNBCe1 is a voltage-dependent Na(+)/nHCO(3)(-) cotransporter that rectifies, independently from the extracellular Na(+) or HCO(3)(-) concentration, around -60 mV. Na(+) removal (0Na(+) prepulse) is necessary to produce the true HCO(3)(-)-elicited current. HCO(3)(-) addition results in huge outward currents with quick current decay. Kinetic analysis of HCO(3)(-) currents reveals that fNBCe1 has a much higher transport capacity (higher maximum current) and lower affinity (higher K(m)) than human kidney NBCe1 (hkNBCe1) does in the physiological range (membrane potential = -80 mV; [HCO(3)(-)] = 10 mM). In this state, fNBCe1 is in favor of operating as transepithelial HCO(3)(-) secretion, opposite of hkNBCe1, from blood to the luminal side. Thus, fugu-NBCe1 represents the first ortholog-based tool to study amino acid substitutions in NBCe1 and how those change ion and voltage dependence.

Using phenotypic plasticity: focus on “Identification of renal transporters involved in sulfate excretion in marine teleost fish”

for osmoregulating vertebrates, diffusive water loss is an unavoidable consequence of living in seawater. Marine teleost fish drink seawater to offset this diffusive water loss dictated by the steep osmotic gradient between blood and the surrounding seawater, a water loss occurring mainly across the

Effect of salinity level in drinking water on feed intake, nutrient utilization, water intake and turnover and rumen function in sheep and goats.

Twelve adult males of each Baladi goats and Barki sheep were divided, each, into four groups based on body weight. Animals were fed a ration consisted of berseem hay (ad lib) and concentrate feed mixture (at the rate of 1.5% of body weight). Treatments were drinking sea water diluted with fresh water to contain 4.04g, 8.15g, and 12.33g total dissolved salts/100 ml (TDS l-1), for 2nd, 3rd and 4th treatments, respectively along with fresh water (0.42 g TDS l-1) as a control. Feed intake of both sheep and goats increased by increasing level of salinity, while species differences existed (P<0.05). Nutrient digestibility coefficients did not differ significantly due to salinity levels. Salinity levels effect appeared significant (P<0.05) on nitrogen utilization. Water intake increased in response to increasing salinity level till 8.15g TDS l-1, and then decreased at the higher level (12.33 g TDS l-1). Water intake response to load of elevated salt was higher in sheep than goats. Neither ammonia nitrogen nor total volatile fatty acid production were affected by salinity level while species effect was found to be significant (P<0.05 for NH3-N and P<0.0001 for TVFA's). Quadratic regression analysis revealed variations over time of both metabolites due to increasing salinity levels. The ruminal pH values were significantly affected by increasing salinity in drinking water. Both salinity levels (8.15 and 12.33g TDS l-1) showed lower ruminal pH than that of fresh water (0.42g TDS l-1). Drinking fresh water resulted in ruminal pH similar to that of the lowest salinity level (4.04g TDS l-1). Sheep had higher (P<0.0001) ruminal pH value (7.309) than goats (7.156). Turnover rate of fresh water was significantly (P<0.05) lower than water of higher salinity levels. The increments in turnover rate as a result of increasing salt concentrations were 42, 84 and 111% for 4.04, 8.15 and 12.33g TDS l-1, respectively. Sheep turned over more water (12%) than did goats. Relative stabilization of the rumen fermentation appeared to be restored at about the 21st day from the beginning of the treatments.

A review of causal factors and control measures for bloat in farmed salmonids with a suggested mechanism for the development of the condition

A mechanism for the development of bloat in salmonids is proposed and explained in terms of the physiology of digestion and osmoregulation in fish. Understanding the causal factors for bloat enables control measures to be identified. In farmed salmonids, the chyme produced during the digestion of nutrient-rich pelleted foods that rapidly disintegrate in the stomach will be a potent activator of a negative feedback mechanism (enterogastric control), which slows stomach emptying to protect the small intestine from nutrient overload. In saline environments salmonids continuously drink sea water to replace fluid lost across the gills. Fluid loss is increased during periods of stress caused by factors such as low oxygen levels, elevated temperature or high salinity. When ingestion of nutrient-rich food results in prolonged activation of enterogastric control, slowed stomach emptying leads to decreased absorption of water, thirst and increased drinking. This further exacerbates stomach distention. The proposed mechanism for the development of bloat is supported by on-farm experience where measures to control bloat include reducing food intake, altering the composition of the diet and using appropriate strategies to reduce stress.

Salt and water regulation by the leatherback sea turtle Dermochelys coriacea.

We measured the salt and water balance of hatchling leatherback sea turtles, Dermochelys coriacea, during their first few days of life to investigate how they maintain homeostasis under the osmoregulatory challenge of a highly desiccating terrestrial environment and then a hyperosmotic marine environment. Hatchlings desiccated rapidly when denied access to sea water, with their hematocrit increasing significantly from 30.32+/-0.54 % to 38.51+/-1.35 % and plasma Na(+) concentration increasing significantly from 138.2+/-3.3 to 166.2+/-11.2 mmol l(-1) in 12 h. When hatchlings were subsequently put into sea water, hematocrit decreased and plasma Na(+) concentration was unchanged but both were significantly elevated above pretreatment values. In other hatchlings kept in sea water for 48 h, body mass and plasma Na(+) concentration increased significantly, but hematocrit did not increase. These data show that hatchlings were able to osmoregulate effectively and gain mass by drinking sea water. We stimulated hatchlings to secrete salt from the salt glands by injecting a salt load of 27 mmol kg(-1). The time taken for secretion to begin in newly hatched turtles was longer than that in 4-day-old hatchlings, but the secretory response was identical at 4.15+/-0.40 and 4.13+/-0.59 mmol Na(+) kg(-1) h(-1) respectively. Adrenaline and methacholine were both potent inhibitors of salt gland secretion in a dose-dependent manner, although methacholine administered simultaneously with a subthreshold salt load elicited a transient secretory response. The results showed that hatchling leatherbacks are able to tolerate significant changes in internal composition and efficiently use their salt glands to establish internal ionic and water balance when in sea water.

Experimental evidence of seawater drinking in juvenile hooded (Cystophora cristata) and harp seals (Phoca groenlandica).

This study was undertaken to measure whether young harp seals (Phoca groenlandica) and hooded seals (Cystophora cristata) drink seawater and, if so, to investigate how the excess salt load is handled. Blood and urine samples were collected from hooded seal pups (n = 3) and harp seal pups (n = 3) after 2 weeks of freshwater exposure, at intervals during 3 weeks of seawater exposure and, finally, after 2 weeks of re-exposure to fresh water. Total water turnover, as measured by injection of tritiated water, was 2200 ml x day(-1) and 3300 ml x day(-1) in hooded seals and harp seals, respectively. The extent of mariposia was taken as the difference between total water turnover and influx of water through food (free and metabolic water) and respiratory water exchange. Seawater drinking amounted to 14% and 27% of total water turnover (rH2O) for the hooded seals and harp seals, respectively. Further evidence of mariposia was obtained from an increase in the excretion rate of the urine osmolytes Na+, Cl- and Mg2+, during the period of seawater exposure. It is concluded that water influx due to seawater drinking can not be excluded as a source of error when estimating food consumption of free-ranging harp seals and hooded seals, by use of labeled water techniques.

Osmoregulatory mechanisms of the Australian freshwater crocodile, Crocodylus johnstoni , in freshwater and estuarine habitats

The estuary of the Limmen Bight River in Australia's Northern Territory is home to an unusual salt water-adapted population of the Australian `freshwater' crocodile, Crocodylus johnstoni. Crocodiles were captured from tidal reaches of the estuary ranging in salinity from 0.5–24‰ and from several permanent fresh water reaches more or less remote from saline waters. C. johnstoni is an effective osmoregulator in moderately saline waters and has osmoregulatory mechanisms very similar to its more marine-adapted relative, the estuarine crocodile Crocodylus porosus. Fasted C. johnstoni in brackish water appear to lose little sodium in cloacal urine, relying on their lingual salt glands for excretion of excess sodium chloride. The lingual glands show clear evidence of short-term and long-term acclimation to salt water. Like estuarine crocodiles, C. johnstoni drinks fresh water and will not drink sea water. Gross sodium and water fluxes in brackish water are very similar to those in other crocodilians, suggesting differences in integumental permeability are not a major influence on osmoregulatory differences between crocodilians. The data reinforce the hypothesis that crocodylids differ fundamentally from alligatorids in the structure and function of the renal-cloacal-salt gland complex and are of interest in current debate over the evolutionary and zoogeographical history of the eusuchian crocodilians.

The eyes have it

Life on land stemmed from life in the sea, but many creatures have since taken the reverse route. A big problem to be overcome was that the body fluids of terrestrial animals are much less salty than sea water. Water can be replaced by drinking sea water, but the excess salt has to be excreted. A newly described fossil turtle not only extends the fossil record of marine turtles back to 110 million years ago, but displays evidence that it had massive salt-excreting lachrymal glands that were its passport back to the sea.

胃内温変化から見た産卵期アカウミガメの摂餌

The presence of feeding was examined in loggerhead turtles during internesting periods from 1989 through 1993 off southern Japan using the Time Temperature Recorder (TTR). The TTR was inserted into the stomach and temperature data were obtained from the nine free-ranging female loggerheads. The patterns of temperature fluctuation which consisted of a rapid drop and subsequent gradual rise were recorded in the stomach temperature data. This typical pattern proved to be caused by drinking or feeding. The pattern counted 5 to 19 times in the first 24 hours after nesting and decreased afterwards gradually. The loggerheads seemed to drink sea water just after nesting and not to feed during internesting periods.

Drinking and water absorption by the larvae of herring (Clupea harengus) and turbot (Scophthalmus maximus)

The efficiencies of water absorption from the guts of the larvae of herring (Clupea harengus L.) and turbot (Scophthalmus maximus L.) were estimated by two methods, The first method was based on the differences in the rates of accumulation, by drinking, and clearance from the gut of radiolabelled inert markers. The second method used the equilibrium level of radioactivity in the larvae to measure the concentration of the markers in the gut above background as water is absorbed from the gut. Water absorption efficiencies for herring larvae drinking sea water were estimated to be 77% using both methods. When external salinity was reduced to 50% sea water, drinking rates and water absorption efficiency in herring larvae fell substantially.Estimates of water absorption efficiency of seawater‐adapted turbot larvae were similar (71–84%) to that of herring using both methods. Although temperature had a marked effect on both the rate of drinking and water absorption, there was no significant thermal effect on the efficiency of absorption from the guts of turbot larvae. The limitations of the techniques and the implications of the estimates in terms of water balance in fish larvae are discussed.

Renal, respiratory and ionic regulation in Atlantic salmon (Salmo salar L.) kelts following transfer from fresh water to seawater.

Atlantic salmon may return to the sea after spawning in fresh water. These fish, known as kelts, reportedly show a limited ability to hypoosmoregulate. However, this study shows that fresh-water-adapted kelts exposed to seawater demonstrate rapid adaptation (within 48 h) in osmoregulatory parameters to values characteristics of seawater-adapted salmonids. The urine flow rate falls from 1.2 to 0.2 ml.kg-1.h-1 within 24 h. Over the same period, urine osmolality increases from 48 mosmol.kg-1 to become isosmotic with the plasma, and Mg2+ secretion by the kidney tubules elevates the urine concentration from 0.5 to 100 mmol.l-1. As is characteristic for marine teleosts, kelts drink seawater and process the ingested water in the gut to replace body water lost by osmosis to the hyperosmotic medium. Seawater exposure causes a marked hypoxia, arterial oxygen tension falling by 43% within minutes and persisting for at least 4 days at this low level. This is associated with large changes in blood pH and acid-base balance. The physiological mechanisms involved in adaptation to a hyperosmotic external medium are discussed, and the osmoregulatory capacity of kelts is compared with that of salmon at other stages of the life cycle.

Seawater Consumption and Water Economy of Tropical Feral Goats

Feral goats (Capra hircus) on the tropical atoll of Aldabra, Republic of Seychelles, were observed drinking seawater at the end of extended dry periods when no fresh water was available. These observations represent the first documentation of voluntary consumption of seawater by an ungulate under natural field conditions. The kidneys of the goats showed no unusual gross morphology. In addition to consuming seawater, the goats produced relatively dry feces and fed on plants with relatively high water content. ALTHOUGH NUMEROUS MAMMALS have been given saline drinking water of various concentrations to study their renal efficiency and salt tolerance, documented cases of mammals voluntarily drinking seawater under natural field conditions are rare. Confirmed, voluntary consumption of seawater in the wild has been reported only for the tammar wallaby, Macropus eugenii (Kinnear et al. 1968, Purohit 1971). Dorcas gazelles, Gazella dorcus (Ghobrial 1976) and feral goats, Capra hircus (Dunson 1974), seen on beaches in arid environments, were presumed to have been drinking seawater. Populations of feral goats have become estab

Role of the Lower Intestine in the Adaptation of Gulls (Larus Glaucescens) to Sea Water

ABSTRACT We used in vivo perfusion of the lower intestine (colon plus coprodeum) to examine the osmoregulatory role of that organ in glaucous-winged gulls (Larus glaucescens Naum.) drinking sea water and fresh water. The area of the lower intestine was small, 0·59 cm2 100g-1 body mass. Its electrolyte and water transport rates were unaffected by salt water acclimation. Sodium and chloride were always reabsorbed from the intestinal lumen to the plasma. The maximum sodium transport rate we measured was 37μlequivcm-2h-1, from a sodium concentration of 200 mequiv l-1. Potassium transport from the different perfusion fluids differed, and was generally negatively correlated with sodium transport, suggesting some form of sodium-potassium exchange. Solute-linked water was reabsorbed at a rate of 3·5 μlμequiv-1 Na+, permitting the lower intestinal epithelium to maintain a luminal fluid up to 130mosmolkg-1 hyperosmotic to plasma. The serosal-to-mucosal osmotic permeability coefficient of the lower intestinal epithelium was 0·21 μlcm-2h-1 (mosmolkg-1)-1. Ureteral urine from birds in both groups was usually strongly (up to 250mosmolkg-1) hypertonic to plasma, but sodium, potassium and chloride concentrations were low and constituted less than 25 % of total osmolytes. We suggest that the lower intestine of L. glaucescens does not play a major role in reclaiming urinary water and electrolytes for recycling to the salt glands.

Sea water drinking as a homeostatic response to dehydration in hatchling loggerhead turtles Caretta caretta

1. 1. Hatching Caretta caretta may lose up to 12% of their initial hatched weight from water loss during emergence from the nest. 2. 2. After subsequent osmotic and excretory water loss in sea water, hatchlings will drink sea water (166 μl 100 g −1 hr −1) and return to their initial weight within 10–15 days, without feeding. 3. 3. There were no significant changes in plasma osmolarity or sodium levels over this period. 4. 4. This osmoregulatory strategy is in marked contrast to that seen in the estuarine crocodile, Crocodylus porosus.

Osmoregulation in Nestling Glaucous-Winged Gulls

-Blood samples from 32 nestling Glaucous-winged Gulls (Larus glaucescens) ranging in age from 1 to 41 days were collected at a nesting site near Vancouver, B.C. The hematocrit was positively correlated, the plasma sodium and chloride concentrations negatively correlated, and the plasma potassium and osmotic concentrations uncorrelated with age. Salt gland secretion was elicited in 23 young gulls by intravenous injection of I M NaC1. The concentration and the volume of secretion increased with age. Sodium secretion was positively correlated with the size of the salt gland. The secretion of potassium and minimum maintained concentrations of sodium were positively correlated with age. In the first hour of secretion, hatchlings eliminated 39% of the injected fluid containing 24% of the injected sodium; in contrast, the oldest nestlings removed 77% of the fluid and 55% of the sodium. Cloacal fluid voided by older salt-loaded birds was less concentrated than that of younger ones. Organ weights were determined in 20 nestlings. Kidney weight was 2-3% of the body weight regardless of age, but the relative weights of the Harderian, salt, and adrenal glands decreased with age. From the time they begin to feed, young marine birds consume foods that are hyperosmotic to their body fluids and must, therefore, eliminate excess solutes (mainly sodium and chloride) in order to remain in osmotic balance. Adult birds of marine species eliminate excess sodium chloride by means of the salt glands (Peaker and Linzell 1975), the secretion of which has roughly twice the concentration of sea water. Thus, they can drink sea water or eat salt-rich foods and still maintain osmotic balance. Adult birds also have other osmoregulatory options: e.g., they can select food items and so, theoretically at least, regulate their salt intake; those living along the coast also have access to fresh water. In contrast, nestlings do not have these choices although their parents could select food of low osmotic concentration or extract salts from it before feeding it to them. However, my observations of the food (often whole small fish or mussels) regurgitated by nestlings suggest that the adults do neither of these things. Nestlings do not ordinarily have access to water, although they have been reported to eat grass, which may provide them with free water (Ensor and Phillips 1972). They may also use dew or the parents may bring them fresh water, although neither of these possibilities seems to have been substantiated. Hence, nestling marine birds probably rely heavily on extrarenal secretion to excrete excess salt. Little has been reported about the rate of maturation of the secretory process or the factors that affect it in such nestlings. Douglas (1968) examined the size and secretory capacity of salt glands from Ad6lie Penguin chicks (Py oscelis adeliae). He found that the gland's weight and secretory rate were linearly correlat d with body size, but that the chloride concentration of the secretion was constant hroughout the growth period. He noted secretion in pipping chicks and suggested that ev n at this age, they were capable of handling the excess salt in their diet of marine inverteb es. Hughes (1968) also found that the salt gland of Common Tern chicks (Sterna hirundo) enlarged in linear fashion with body size, even though older birds were less efficient at excreting imposed salt loads than younger ones. This was due to a decrease in the volume secreted by the salt gland, not in the concentration of the secretion. However, some of the birds in that study were salt-loaded more than once during their growth period and this may have influenced their responses. Ensor and Phillips (1972) compared the secretory capacities of salt glands from 4to 5and 15to 16week-old chicks in two mixed populations of gulls (Larus argentatus and L. fuscus) that had been raised either on a marine island or an inland freshwater site. The younger birds from the marine environment were smaller than their freshwater counterparts and had larger salt glands, nearly twice as large on a weight-specific basis. The secretion of their glands was twice as concentrated in sodium and was produced at three times the rate of that from freshwater birds. These differences disappeared by the time the birds were 15-16 weeks old. In the present study, I examined the blood of birds at representative stages of the entire maturation period for age-related changes in hematocrit, electrolyte concentration, and os-

Chemistry of the body fluids of the coelacanth, Latimeria chalumnae.

The coelacanth, Latimeria chalumnae , possesses a blood chemistry that is nearly identical to that of the elasmobranch fishes and contrasts with that of the bony fishes and tetrapods. Especially notable is the retention of high concentrations of urea (377 mM) and of trimethylamine oxide (122 mM), which aid in raising the blood osmolarity (942 mosm/I) to close to that of the sea water environment. These features also characterize other coelacanth body fluids, such as the notochordal fluid, aqueous and vitreous humours, ventricular fluid, coelomic fluid and bile. The tissues of Latimeria , such as muscle, are also characterized by high urea concentrations. The osmotic balance between extracellular fluids and tissues seems to be achieved by the presence of very high tissue levels of trimethylamine oxide ( ca . 300 mmol/(kg H 2 O)), which counteract the low ion concentrations found in tissue. Renal function in Latimeria seems to involve the selective elimination of certain divalent ions (magnesium, phosphate and sulphate) and of organic substances (glucuronate, creatine and some amino acids). Unlike other ureosmotic fishes, the coelacanth does not possess the renal capacity to reabsorb urea. Evidence suggests that the rectal gland, structurally much like those of chondrichthyians, functions to excrete excess sodium chloride. Since the blood osmolarity of Latimeria is some­what lower than that of sea water (942 cf. 1026 mosm/l), it is in negative water balance. Some evidence suggests that this is overcome by drinking sea water in a manner similar to that of the teleosts. The problem of whether ureosmotic regulation is homologous in Latimeria and the chondrichthyians is moot, although we favour the possibility that it was independently acquired for the following reasons. (1) Renal urea reabsorbtion is absent in Latimeria although it is crucial to ureosmotic regulation in the chondrichthyians. (2) Internal fertilization and development are necessary concomitants of ureosmotic regulation in fishes and internal fertilization in the two groups is achieved by non-homologous mechanisms. (3) Ureosmotic regulation has been evolved independently in a third vertebrate group, the euryhaline amphibian Rana cancrivora .

The Provision of Potable Water by Solar Distillation

SynopsisThe relevance of fresh water in shipwreck survival conditions is shown with reference to the physiological effects of drinking sea water. The principles, construction and performance of solar distillation plants are discussed. The reliability and fresh-water costs from this method of desalination are put in perspective with those of conventional distillation processes. It is shown that installations with capacities up to 38 m3 (10 000 UK gallons/day) can be viable with other more complicated desalination processes.

Water Balance in California Sea Lions

which these animals haul out are truly desert islands, as dry and nearly as hot as the nearby mainland. These sea lions have no access to fresh water. The question naturally arises, do they drink sea water? If they drink sea water, they must somehow get rid of the salts. If they do not, then they must somehow get rid of the large amount of fixed nitrogen which their carnivorous diet yields as a waste product. If they eat invertebrates such as squid, then they must excrete not only the nitrogen wastes but also the excess salts, for, unlike fish, invertebrates are commonly thought to have a salt concentration in the body fluids which is similar to that of sea water.