OSMOTIC CONSTITUENTS OF THE COELACANTHLATIMERIA CHALUMNAESMITH

Abstract

The coelacanth Latimeria chalnmiiae occupies a unique position in the phylogenetic tree of the vertebrates as the only living representative of the crossopterygians, a group generally thought to lead from the ancestral bony fishes to the amphibians (Berg, 1958;Young, 1962; Romer, 1966). This, together with the fact that until 1939 the crossopterygians had been considered long extinct, dying out in the Cretaceous, accounts for the great interest shown in these "living fossils." However, in spite of an almost continual search since the end of the Second World War only two females and 30 males have been found to date, and there has been chemical analysis on only one specimen. On this fish, a large frozen male, Pickford and Grant (1967) analyzed the blood, Brown and Brown (1967) searched for the ornithine cycle enzymes and urea in the liver, and Cowgill, Hutchinson and Skinner (1968) looked at the mineral content of its hard and soft tissues. The offer to us by the Royal Scottish Museum of access to another specimen was therefore accepted with enthusiasm and it was thought worthwhile to confirm and perhaps extend the results on the first. As our fish was also frozen a small study was made to find the gross effect of prolonged freezing on the distribution of ions in a common fish (the freshwater perch) to help us interpret our data. MATERIALS AND METHODS141, 553-560.

Composition of the Blood Serum of Deep-Sea Fishes

“…All marine elasmobranchs retain high levels of urea (Smith, 1936;Pang et al, 1977;Holmes and Donaldson, 1969). This is also characteristic of holocephalans (Read, 1971a;Fange and Fugelli, 1963;Robertson, 1976) and the coelacanth (Pickford and Grant, 1967;Lutz and Robertson, 1971;Griffith, 1980). In these groups urea brings osmolarity close to that of sea water while maintaining blood electrolytes at levels much lower than sea water.…”

Muscle Proteins of the CoelacanthLatimeria ChalumnaeSmith

“…These last determinations on various tissues have made it clear that the coelacanth is adapted to sea water in a similar manner to the elasmobranchs, by way of urea retention. The urea and trimethylamine oxide contents of the muscle, amounting respectively to 0-42 and 0-29 moles/kg muscle water, are the highest yet recorded and represent together 70% of the total osmolality of the tissue which appears to be in approximate equilibrium with the sea water (Pickford & Grant, 1967;Lutz & Robertson, 1971). Coelacanth muscle contains, on the other hand, large extracellular wax ester depots as in the case of other bathypelagic species (Nevenzel et al 1966).…”

“…Except from the anatomical point of view (Millot & Anthony, 1958, few investigations have been made on coelacanth muscle. Until recently, the only biochemical determinations available were related to the lipid content (Nevenzel et al 1966), the elementary composition (Cowgill, Hutchinson & Skinner, 1968) and the osmotic constituents (Lutz & Robertson, 1971). These last determinations on various tissues have made it clear that the coelacanth is adapted to sea water in a similar manner to the elasmobranchs, by way of urea retention.…”

“…An analysis was originally performed on each dialysate, but as no significant differences were found between the relative amounts of the constituents, the results were pooled (Table 2). They are expressed in millimoles per kg muscle water assuming a water content of 73-7° 0 (Lutz & Robertson, 1971) and no evaporation during storage. The sum of the amino acids and urea contents are low and at variance with the figures given by Lutz & Robertson (1971) using different methods of evaluation.…”

Mechanism of biosynthesis of trimethylamine oxide in tilapia reared under seawater conditions

“…1 However, negligible quantities have been reported in the tissue of freshwater fish. Cod Gadus morhua , sharks, rays, skate and squid possess TMAO at particularly high levels.…”