Ruth Lotan

Osmotic adjustment in the euryhaline teleostAphanius dispar (Cyprinodontidae)

SummaryOsmotic pressure and concentration of chloride, sodium and potassium in plasma and total water contents in the euryhaline teleostAplianius dispar were examined.In different salinities the osmotic pressure and chloride concentration change significantly: osmotic pressure was 366.1 μOsmole/gram in fresh water and 681 μOsmole/gram in 400% sea water. Chloride 137 μM/gram in fresh water and up to 285.7 μM/gram in 400% sea water.The sodium concentration was relatively stable: 169 μM/gram in fresh water, 205.6 μM/gram in 300% sea water.The water content in all media examined remained constant at about 74% of wet weight, and only at 100% of sea water it was 72.4%.

Sodium, chloride and water balance in the euryhaline teleost Aphanius dispar (Rüppell) (Cyprinodontidae)

Summary1.Sodium, chloride and water balance were measured in fresh water, 100% sea water and 200% sea water.2.It was found that the total amount of sodium and chloride decreases with the decrease of the salinity in the medium; minimum water content was found in 100% sea water.3.The sodium flux is high in sea water and reduced in fresh water. Chloride flux reached only 50% of that of sodium.4.Maximum water flux was found in 100% sea water, about 66% of body weight. It was only 50% of body weight in fresh water and in 200% sea water.5.Drinking rates are correlated with the salinity of the media; the drinking rates rise with a rise in salinity. The amount of drinking water was found to be only a small percentage of total water flux.6.It was concluded that the most important osmoregulatory mechanism in A. dispar is the change of sodium and chloride content in its body when there are changes of salinity in the medium.

The pituitary of Aphanius dispar (Rüppell) from hypersaline marshes and freshwater

SummaryAn ultrastructural study of the rostral pars distalis of the pituitary of Aphanius dispar specimens taken from freshwater or hypersaline marshes revealed significant structural differences which indicate higher activity of the prolactin cells in the hypotonic medium. Prolactin cells from freshwater specimens had larger secretory granules, a higher amount of endoplasmic reticulum, and expanded intercellular spaces with many secretory lakes. These cells contained an unusual cytoplasmic structure, consisting of twisted canals with vesicular lumina, connected to the endoplasmic reticulum of the cell. This structure is about 1–2 μm in diameter.Stellate cells are characterized by extracellular spacing junctions which are particularly noticeable at the confluence of the interstellate cell canaliculi and the pericapillary space.

Osmoregulation during adaptation to fresh water in the euryhaline teleostAphanius dispar rüppell (Cyprinodontidae, pisces)

Summary1.The electrolyte concentration and water content of plasma and muscle have been measured during adaptation to fresh water, after transfer from 300% sea water.2.The process of adaptation can be divided into three phases.A.The first hour after transfer are characterized by a rapid loss of electrolytes from plasma and muscle, and a decrease of water content in plasma, and increase in the water content of the muscle.B.The period 1 to 48 hours after transfer is characterized by a reduced loss of electrolytes, together with further increase of water in muscle.C.The period beginning 48 hours after transfer is characterized by an increase of electrolytes in plasma and muscle, together with decrease of water content in muscle, until equilibrium is reached.3.Changes in “Chloride space” and electrolyte distribution in muscle were also observed.

OXYGEN CONSUMPTION IN THE GILLS OF TILAPIA AUREA (STEINDACHINER) (PISCES, CICHLIDAE) IN VARIOUS SALINE CONDITIONS

ABSTRACT A relationship was found to exist between the oxygen consumption of the gills and the osmotic pressure of the blood, in Tilapia aurea (Steindachner) which had undergone prior adaptation to various salinities. At a dilution of 40% sea water and in undiluted sea water, when the osmotic concentration in the blood is low, the oxygen consumption is also low. At a dilution of 60% sea water, the osmotic concentration in the blood is high, and so is the oxygen consumption of the gills. At a dilution of 80% sea water, the osmotic pressure in the blood is again low, but the oxygen consumption in the gills remains high. Hence it was concluded that the stimulation of a salinity threshold, above a dilution of 60% sea water, is required for the efficient operation of the regulatory osmotic salt water mechanism.

Intestinal salt and water transport in a euryhaline teleost, Aphanius dispar (Cyprinodontidae)

Abstract 1. 1. The transmural Na+, K+, Cl− and water flow in the total intestine of Aphanius dispar was measured by an in vitro in situ perfusion technique. 2. 2. A neutral NaCl absorption without a net K+ flow was observed; this occurred in the absence of a transmural osmotic difference followed by an isosmotic water absorption. 3. 3. The osmotic permeability coefficient and the NaCl mobility of the intestinal wall seemed high.

DISTRIBUTION AND REPRODUCTION OF KILLIFISH APHANIUS DISPAR AND A. FASCIATUS AND THEIR HYBRIDS IN THE BARDAWIL LAGOON ON THE MEDITERRANEAN COAST OF SINAI, EGYPT

ABSTRACT The Red Sea Aphanius dispar and the Mediterranean Aphanius fasciatus can be found sympatrically in the Suez Canal, in the lakes of Lower Egypt, and along the Mediterranean coast of Israel. Both species are closely related and are known to form hybrids when held together. Putative hybrids of these species were found in the shallow Bardawil Lagoon on the northern coast of Sinai. The lagoon is unique in the eastern Mediterranean by being totally hypersaline without any brackish or freshwater sections. Samples were obtained using a small mesh-size experimental beach seine between April 1973 and March 1975. Among the 4,600 specimens of killifish examined, 45% belonged to A. dispar, 17% to A. fasciatus, and 38% to their putative hybrids. Seasonal abundance was similar in all three taxa; there were few fish during the winter months and from June to October, abundant fish, mostly juveniles, with peaking in July. Examination of gonads revealed that the reproductive period of the two species is from March ...

The pituitary of Aphanius dispar (Rüppell) and its neurosecretory innervation from hypersaline marshes and fresh water

SummaryEta cells of the pituitary of Aphanius dispar specimens adapted to sea water are densely packed and have folded nuclei. Unfolding of the nuclei accompanied by cellular hypertrophy and hyperplasia was observed 24 hours after experimental transfer of specimens into fresh water. In specimens from natural habitats and adapted over long periods to fresh water, the nuclei are rounded and cellular hypertrophy attains maximal values. Dilatation of capillaries in the hypophysis was observed in about one third of the specimens within the first few days after transfer to fresh water. In specimens adapted either to fresh water or to sea water the capillaries were normal. Epsilon cells from seawater specimens have elongated nuclei perpendicular to the basement membrane which separates the rostral neurohypophysis from the adenohypophysis; in freshwater specimens epsilon cell nuclei are rounded.