Robert W. Griffith

Environment and Salinity Tolerance in the Genus Fundulus

A comparison was made of environmental salinities, ability to survive in fresh water and upper salinity tolerance for over 20 species of the teleost genus Fundulus. All species of the genus occur, at times, in fresh water and are able to survive in this medium in the laboratory. Species found in brackish environments have upper salinity tolerances ranging from 74-114%o, while most species characteristic of fresh waters are unable to survive in salinities above 29%o. Notable exceptions are F. zebrinus, an inland species commonly found in saline waters, F. diaphanus, a freshwater form which often enters dilute brackish estuaries and F. waccamensis, a Pleistocene lacustrine derivative of F. diaphanus. Since brackish-water species are tolerant of life in fresh water while the reverse is not the case, it is suggested that freshwater species of Fundulus were derived from fully euryhaline ancestors which gradually lost the ability to live in sea water during extended isolation from brackish or marine environments.

Regulation of gonadal steroidogenesis in Fundulus heteroclitus by recombinant salmon growth hormone and purified salmon prolactin

The effects of recombinant salmon growth hormone (sGH) on plasma sex steroid levels and gonadal function were investigated in hypophysectomized Fundulus heteroclitus. Effects of sGH were compared to those of purified chum salmon prolactin (sPRL), Atlantic salmon gonadotropin (sGTH), and salmon pituitary extract (sPE). Treatment with sGH significantly increased plasma concentrations of testosterone in males and estradiol-17 beta in females; sPRL had similar effects on testosterone levels in males. Further, treatment with these hormones prevented the decline in gonadal weight observed after hypophysectomy in both males and females. In vivo treatment of male fish with sGH also augmented testosterone and 11-ketotestosterone production by testis tissue subsequently incubated in vitro. Direct action(s) on gonadal steroidogenesis was examined by incubating gonadal tissues from hypophysectomized fish in vitro with various hormones. sGH significantly stimulated the in vitro production of testosterone and 11-ketotestosterone by testis, and estradiol-17 beta by ovary. sPE and sGTH also stimulated gonadal steroidogenesis, whereas sPRL and bovine GH had no significant effect. By comparison, rainbow trout gonads also produced increased amounts of steroids when treated with sGH in vitro. The use of a cloned GH rules out contamination by other pituitary hormones. These results, therefore, demonstrate that recombinant salmon growth hormone possesses steroidogenic and gonadotropic activity. Purified sPRL also has steroidogenic and gonadotropic actions. However, the significance of these effects of teleost GH and PRL is not known.

Guppies, toadfish, lungfish, coelacanths and frogs: a scenario for the evolution of urea retention in fishes

The question of how (and why) the ureosmotic strategy, characteristic of Latimeria chalumnae and the chondrichthians evolved is addressed. There are three requirements for ureosmotic regulation: urea synthesis via the ornithine-urea cycle, urea tolerance involving biochemical and physiological adjustments, and urea retention that requires renal, branchial, metabolic and reproductive adaptations. Several examples of lower vertebrates in which urea plays a physiological role are considered to see whether they might provide insight into the origin of ureosmotic regulation. The guppy shows high urea synthesis and retention during embryonic development, and it is possible that a developmental role of urea is a general phenomenon in fishes. The toadfish, thought to be an enigma with high urea synthesis in the absence of an obvious physiological role of urea, is ureotelic under some conditions. Its urea excretion is likely related to renal function and/or parental care. In lungfish high ureogenesis is associated with estivation in periodically dry habitats. The resultant hyperuremia prevents ammonia toxicity, inhibits water loss and may repress metabolism. Latimeria is a classic marine ureosmotic regulator in which urea is used as an osmolyte that allows osmotic equilibrium with sea water while maintaining low ion levels. Adults of the frog, Rana cancrivora, are also ureosmotic regulators in brackish water. A scenario is proposed that suggests how ureosmotic regulation could have evolved in Latimeria and other fishes. The ornithine-urea cycle (composed of an arginine synthetic pathway and a second pathway that splits arginine into urea) occurred in fossil anadromous agnathans. Here the first pathway functioned in the ammocoete-like larvae for the generation of arginine to supplement a protein-deficient diet of algae, whereas the arginase pathway was important in the embryo for vitellin catabolism. Gnathostome evolution was associated with trends towards large eggs and prolonged development, requiring a complete ornithine-urea cycle for ammonia detoxification in embryos. Retention of a complete ornithine-urea cycle throughout adult life (via paedomorphosis) would preadapt any relatively large, sluggish, euryhaline fish for ureosmotic regulation when it was exposed to sea water. It is suggested that ureosmotic regulators evolved from freshwater or anadromous ancestors that entered the marine habitat. Once early ureosmotic regulators were established in the sea there would have been strong selection for internal fertilization and development, as is seen in Latimeria and many elasmobranchs. It is suggested that ureosmotic regulation was a common strategy in Paleozoic marine gnathostomes.

SERUM COMPOSITION OF FRESHWATER STRINGRAYS (POTAMOTRYGONIDAE) ADAPTED TO FRESH AND DILUTE SEA WATER

1. Juvenile freshwater stingrays of the family Potamotrygonidae are unable to survive in salinities in excess of 20.6‰ when gradually acclimated.2. No differences were observed in blood pH or hematological parameters when fish adapted to a salinity of 14.5‰ were compared with freshwater controls.3. Significant increases were found in serum sodium (21%), chloride (21%), calcium (48%), and magnesium (51%). Increases in total CO2 (16%), potassium (21%), and inorganic phosphorus (35%) were not significant on account of high variance. Serum osmolarity increased 69%.4. There was no apparent effect of salinity on serum total cholesterol, organically bound phosphorus, or total carbohydrates. Glucose contributed only 25% of the latter.5. Serum urea was low (1.1 mM/1) as previously reported, and the trend to increase in a saline environment was not osmotically significant.6. Freshwater stingrays are unique among elasmobranchs in possessing significant amounts of a protein with the electrophoretic mobility of human ...

COMPOSITION OF THE BLOOD SERUM OF DEEP-SEA FISHES

Serum osmolarity, chloride, urea, protein, and trimethylamine oxide were measured in 15 shallow water marine teleosts, 6 elasmobranchs, 9 deep benthic teleosts, and 24 midwater teleosts. Amino acids, carbohydrates, phosphate, and hematocrits were determined for some species from these four groups. Elasmobranchs had high osmolarity (1035 mOsm/l) because of high serum urea (363 mM/l), TMAO (66 mM/l), and chloride (295 mM/l). Shallow water teleosts had low osmolarity (444 mOsm/l), chloride (176 mM/l), urea (4 mM/l), and TMAO (14 mM/l). Deep benthic teleosts had higher osmolarities and chloride levels (576 mOsm/l, 242 mM/1) than shallow water teleosts, as did midwater teleosts (561 mOsm/l, 267 mM/1). Serum TMAO was high in benthic (51 mM/l), but not midwater (12 mM/l) teleosts, and urea was low in midwater (1.0 mM/l) and benthic (1.5 mM/l) groups. Stress and morbidity raise osmolarity and chloride in marine teleosts and may account for high values in midwater and benthic fishes, which were sampled after consi...

THE LIFE OF THE FIRST VERTEBRATES

organ systems necessary for the active, sentient life that we associate with vertebrate animals (some zoologists prefer to use the term craniate when referring to vertebrates because it emphasizes those structural advancements that permitted an active life). The major vertebrate advancements are shown in Figure 1, which compares the morphology of amphioxus and of a fish. The advancements include a set of highly specialized sense organs (image-forming

PITUITARY CONTROL OF ADAPTATION TO FRESH WATER IN THE TELEOST GENUS FUNDULUS

1. Eight species and one subspecies of Fundulus native to brackish-water environments fail within 1-10 days following abrupt transfer to fresh water and fail between 1-4‰ when subjected to gradual declines in salinity following hypophysectomy. Intact specimens of most species survive indefinitely in fresh water.2. Of fourteen species of Fundulus and one species of Profundulus typical of freshwater habitats, none fail before one month and some survive for periods of up to one year following hypophysectomy and transfer to fresh water.3. One inland species of Fundulus characteristic of saline and freshwater environments demonstrates a failure pattern intermediate between the brackish-water and fresh water species of the genus.4. In those species tested at two or more different temperatures, low temperature generally prolongs survival in fresh water after hypophysectomy.5. Although hypophysectomy has only minor effects on serum electrolytes (sodium and chloride) in the three species of Fundulus tested in sea ...

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 H2O)), 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.

Effects of recombinant salmon growth hormone on hypophysectomized male Fundulus heteroclitus

Abstract 1. 1. Recombinant salmon growth hormone at doses of 0.8 and 2.1 μg/g significantly enhanced linear growth in hypophysectomized male killifish, Fundulus heteroclitus , over that of controls and a significant regression was found between growth and the logarithm of dose. 2. 2. Bovine growth hormone elicited significant growth enhancement at all three dosages tested (1,4 and 10 μg/g) and a significant log/dose relationship was also observed. 3. 3. Observations on the relative weight of the gonads indicate that whole salmon pituitary extract (25 μg/g) possesses strong gonadotropic activity and that both bGH and rsGH had smaller but significant effects on the gonads. 4. 4. It is suggested that growth hormone may play a subsidiary synergistic role to other pituitary hormones in gonadal development.

Osmotic adaptations of the Chilean clingfish, Sicyases sanguineus, during emertion

Abstract 1. 1. The osmotic adaptations for dehydration of the Chilean clingfish ( Sicyases sanguineus ) were examined in emerged fish. 2. 2. Plasma osmolarity, electrolyte levels, body weight changes, hematocrit, muscle water content and urea were measured at various times up to 24 hr of emersion. 3. 3. At 24 hr of emersion, the gut surface of the fish was reddish with engorged capillaries. The concomitant presence of air in the gut suggests a role for the intestine in the air breathing mechanism. 4. 4. S. sanguineus maintained out of water showed a significant loss of body weight and increases in hematocrit values and plasma osmolarity, urea and electrolyte levels.