The demography of the coelacanth Latimeria chalumnae

Synopsis The very sparse data that are available on the abundance, population structure and biology of the coelacanth Latimeria chalumnae off Grand Comoro are summarised, and some simple numerical analyses are carried out to explore certain aspects of the population dynamics, particularly the age-profile of the population. The object has not been to provide estimates of key demographic parameters, such as mortality rates, but to propose various scenarios that are useful for comparison with real data as they become available. The analysis also makes it possible to reach some preliminary conclusions that are relevant to the management of the coelacanth population. For instance, it appears that the catch rate of coelacanths by artisanal fishermen may have a negligible effect on coelacanth survivorship, and it is more likely that population size and structure are determined by natural mortality rates and birth rates. It is suggested that predation is the main cause of natural mortality and that the main predators of coelacanths are likely to be large sharks. Interference with the traditional patterns of the Comoran artisanal fishery may threaten the coelacanth. Several important gaps in our knowledge of coelacanth demography are identified.     

The ecology and conservation of the coelacanth Latimeria chalumnae

Synopsis Studies on the ecology of the living coelacanth, Latimeria chalumnae, are reviewed and assessed. Early predictions on the life history of the coelacanth have proved to be accurate but recent findings have improved our understanding of its habitat and feeding preferences, diel activity patterns and social behaviour. A history of coelacanth conservation reveals that there has been a sustained concern for the survival of this species which has eventually culminated in several effective conservation actions in recent years. The coelacanth is threatened by a number of socio-economic and biological factors, but international action directed at managing the fishery in the Comoros should ensure that the species survives. Recent observations on living coelacanths in their natural environment have greatly improved our knowledge of the behaviour and relative abundance of adults. Important priorities for future research include studies on the distribution and abundance of juveniles and breeding adults, both off the Comoros and elsewhere. The coelacanth is a highly specialised, precocial fish which occupies a unique place in biology. Co-ordinated international efforts should continue to be made to understand and conserve this remarkable fish.     

Bile salts of the coelacanth, Latimeria chalumnae

Bile salts of the coelacanth, Latimeria chalumnae, Smith, have been analyzed and shown to have three bile alcohols, latimerol, 5 alpha-cyprinol, and 5 alpha-cholestane-3 beta, 7 alpha,-12 alpha,25,26-pentol, two C24 bile acids, chenodeoxycholic acid and cholic acid, one C26 bile acid, probably 3 beta, 7 alpha, 12 alpha-trihydroxy-27-nor-5 alpha-cholestan-26-oic acid, and two C27 bile acids, 3 alpha,7 alpha,12 alpha-trihydroxy-5 alpha-cholestan-26-oic acid and 3 beta,7 alpha,12 alpha-trihydroxy-5 alpha-cholestan-26-oic acid as determined by gas-liquid chromatography and gas-liquid chromatography-mass spectrometry.     

Juvenile anisakine parasites from the coelacanth Latimeria chalumnae

Synopsis Two coelacanths captured in waters off of the Comoro Islands were examined for parasites. Eight third-stage anisakines of the genus Terranova or Pulchrascaris were found in the spiral valve and rectum of the two coelacanths examined. The poor condition of these defrosted specimens prevented further identification. The depauperate parasitofauna in coelacanths may result from their unique physiology and morphology and because they are a relict fish that has survived millions of years beyond other relatives and potential intermediate hosts.     

Viviparity and the maternal-embryonic relationship in the coelacanth Latimeria chalumnae

Synopsis Embryos of Latimeria chalumnae develop in well-vascularized compartments in the uterine region of the right oviduct. Compartments conform to the shape of their embryos and yolksacs; they represent a stable, gestation-induced oviductal modification. Late-term pups possess large, flaccid, vascular yolksacs almost devoid of yolk. The sac is in close contact with, but does not adhere to, the lumenal uterine surface. A massive vascular plexus occurs in the wall of the compartment at the site of contact with the yolksac; together they constitute a non-adherent, transposable placenta. The exterior surface of the yolksac is bounded by an attenuated, single-layered, squamous epithelium that surrounds an intercommunicating bed of cortical sinuses. The cortex of the sac is composed mostly of connective tissue stroma. The inner surface is bounded by a layer of yolk-digesting merocytes. Residual yolk occurs as yolk platelets that include yolk crystals. The interior surface of the sac is invested by an uniquely specialized vitelline circulation; no connection seems to exist between the interior of the yolksac and gut. The uterine wall consists of: (1) a lumenal surface composed of an anastomosing network of capillaries with a layer of attenuated, very thin, squamous epithelium, (2) a well-vascularized connective tissue stroma, (3) alternating transverse and longitudinal layers of smooth muscle, also well-vascularized, and (4) an external epithelial layer. Comparison of egg dry weight (184 g) with the estimated dry weights of a late-term pup (171 to 239 g) and a neonate (200 to 280 g) reveals a weight change of – 7 to + 30% and + 9 to + 52%, respectively. This is indicative of matrotrophy. In one female specimen, 19 remarkably large ovulated eggs were found and in another about 30 somewhat smaller ovarian ones. These are many more than ever could be accommodated in the uterine space. During the early and middle phases of development, embryos must be lecithotrophic, using their yolk reserves, with oophagy of fragmented supernumerary eggs as the most probable source of additional nutrients. The well-developed embryonic gut contains brown, amorphous yolk-like material. The limited amount of metachromatic secretory product of the uterine glands can play little or no role in embryonic nutrition.     

Enzymes of the coelacanth Latimeria chalumnae evidenced by starch gel electrophoresis

Synopsis The coelacanth, Latimeria chalumnae, is often referred to as a living relic. The opportunity to examine its biochemical molecular structure was sought in an effort to define the degree of its genetic variability. The coelacanth is thought to live only in a small area around the Comoro Islands in the Western Indian Ocean. The scenario presented suggests that the coelacanth may have lost genetic variability as a result of genetic drift within a small population. The narrow geographic range of the coelacanth suggests adjustment to a relatively limited environment. The loss of specific alleles through genetic drift can reduce the ability of a fish population to adapt to changes in environmental conditions. The coelacanth needs strong conservation measures to be taken to curtail the capture of specimens and for the protection of its limited natural habitat.     

Habitat and population size of the coelacanth Latimeria chalumnae at Grand Comoro

Synopsis In 1987 and 1989 coelacanths were observed for the first time in their natural habitat with the help of submersibles. Coelacanths were found between 150–253 m depth, their preferential depth seems to be around 200 m; the water temperature ranged between 16.5–22.8° C. During the day coelacanths aggregate in small non-aggressive groups in sheltered lava-caves. Caves might be a limiting factor for distribution. At night they leave the caves for hunting by drifting singly along the steep lava slopes. They migrate between different caves located within a large home range covering more than 8 km coastline. Coelacanths are site-attached, some for a period of at least 2 years. Our own observations and earlier catch records show that only the west coast of Grand Comoro is a suitable coelacanth habitat with more structural complexity and prey fish abundance than other coastlines of the island. From our survey we estimated a total coelacanth population off Grand Comoro to be 150–210 individuals; a saturated population would be 370–510 individuals. This small relict population seems to be stable. International protection of coelacanths against commercial interests is needed     

Ultrastructure of the integumental melanophores of the coelacanth,Latimeria chalumnae

The integumental melanophores of Latimeria chalumnae were studied by light and electron microscopy. The epidermal melanophore located in the mid-epidermis consists of a round perikaryon with long slender dendrites extending into epidermal cells and intercellular spaces. The dermal melanophores occur in the loose dermal matrix underlying a relatively thick layer of collagen fibers. The dermal melanophores are usually flattened and their dendrites lie parallel to the collagen layer. Both epidermal and dermal melanophores contain oval, electron-opaque melanosomes, large mitochondria, agranular vacuoles of endoplasmic reticulum and microtubules. Microfilaments and RNP particles are less conspicuous. While the peripheral cytoplasm of both dermal and epidermal melanophores is filled with a large number of melanosomes, the perinuclear cytoplasm of many dermal melanophores is occupied by premelanosomes in various stages of differentiation, and that of the epidermal melanophore contains numerous large vacuoles. Despite the scarcity of epidermal melanophores, the epidermal melanin unit is present in the form of melanosome complexes. In addition, the melanophores of Latimeria possess the basic characteristics common to other vertebrates, but they more closely resemble those of lungfish and other aquatic vertebrates.     

Occurrence of organochlorine contaminants in tissues of the coelacanth Latimeria chalumnae

Synopsis Gas chromatography coupled with electrolytic conductivity detection and electron capture negative chemical ionization mass spectrometry have been used to identify and quantify organochlorine xenobiotics in tissues from two specimens of the living coelacanth Latimeria chalumnae. Compounds identified include polychlorinated biphenyls (PCB), 4,4-DDT and its metabolites 4,4-DDD and 4,4-DDE. Levels of these compounds in the specimens were observed to be generally related to tissue lipid content. Highest concentrations of the xenobiotics were present in the lipid-rich swim bladder, followed by adipose tissue and liver. Levels ranged from 89 to 510 g kg^–1 for PCB and 210 to 840 g kg^–1 for -DDT (including DDD and DDE) on a wet-weight basis. Organochlorine concentrations in relatively lipid-poor tissues, i.e. muscle and kidney, were lower. Parent DDT contributed significantly to the -DDT burden. PCB congeners containing five to seven chlorines were most prevalent. Component distributions did not match those present in common commercial PCB formulations. However, major congeners observed were similar to those reported for other fishes.     

Chemical characterization of the brain of a coelacanth,Latimeria chalumnae

• 1.1. The chemical composition of coelacanth brain was studied and compared with some other species of bony fishes.
• 2.2. Almost all lipid classes generally seen in vertebrate brains were detected: 22:1 and 22h:1 acids were abundant in cerebroside and 24:1 acid in ganglioside. The hydroxy fatty acid content of cerebroside was high.
• 3.3. The myelin protein composition was unusual in that a 28,000-dalton protein was a major component.
• 4.4. 2′,3′-Cyclic nucleotide 3′-phosphodiesterase was 10 times more active than in the other bony fishes.
• 5.5. The present data suggest that molecular construction of coelacanth myelin is more advanced than that of the other bony fishes.

     

Bibliography of the living coelacanth Latimeria chalumnae,with comments on publication trends

Synopsis A list of published references on the coelacanth Latimeria chalumnae is provided. All known publications in the scientific literature are included as well as popular articles and press reports that are considered to provide new information or interpretations. Marked trends are noticeable in the literature as different disciplines have been applied to research on the coelacanth over the past five decades. The bibliography lists a total of 823 publications including 490 papers in journals, 37 books, 3 theses, 45 chapters in books, 166 popular articles, 22 reports and 60 newspaper articles. Studies on taxonomy and morphology initially dominated the literature followed by reports on research in the fields of physiology, behaviour, breeding biology, ecology and conservation as frozen and eventually live specimens became available for study. The literature on the living coelacanth is predominantly in English, French, Japanese and German but references in 12 other languages were also traced. The dominant authors in the first decades of coelacanth research were the French scientists J. Millot and J. Anthony and the South African describer of the first and second coelacanths, J.L.B. Smith. In subsequent years French, British, American, South African, Japanese, Canadian and German authors, among others, have made significant contributions.     

Structure of the kidney in the coelacanth Latimeria chalumnae with reference to osmoregulation

The morphology of the nephrons of the coelacanth Latimeria chalumnae was investigated by light microscopy. Each nephron is composed of a large renal corpuscle with well‐vascularized glomerulus, non‐ciliated neck segment, proximal convoluted tubule divided into distinct first and second segments, non‐ciliated intermediate segment, distal tubule, collecting tubule and collecting duct. The parietal layer of the Bowman's capsule of the renal corpuscle is composed of low cuboidal cells. The short non‐ciliated neck segment is lined by cuboidal epithelium. The first and second proximal segments display a prominent brush border and contain amorphous material in their lumen. The second proximal segment differs from the first segment in having taller columnar epithelium and a relatively narrow lumen. The intermediate segment is lined by non‐ciliated columnar epithelium and its lumen appears empty. The distal tubule is narrow in diameter and its cuboidal epithelium is devoid of intercalated cells. A unique feature of L. chalumnae is having binucleate cells in the tubule and collecting duct epithelium. The renal arteries have poorly developed tunica media and its cells contain granular material. The structure of L. chalumnae nephrons correlates well with their osmoregulatory function and resembles those of euryhaline teleosts.     

Central nervous system myelin proteins of the coelacanth Latimeria chalumnae: phylogenetic implications

Synopsis Myelin was isolated from the brain of a coelacanth. Its protein components were separated by polyacrylamide gel electrophoresis in the presence of sodium dodecylsulfate (SDS-PAGE). A protein component of 25000 Dalton was predominant; it was not glycosylated but reacted moderately with anti-mammalian CNS myelin proteolipid protein (PLP) antibodies and weakly with anti-lungfish CNS myelin glycosylated proteolipid protein (gPLP) antibodies. A component equivalent to mammalian DM-20 was not detectable. Presumably due to autolysis myelin basic protein (MBP) was not discernible by protein staining but showed up as a single band of 17000 Dalton with anti-mammalian MBP antibodies. Wolfgram protein (WP) was not present upon immunoblotting and the values for the myelin-specific 2, 3-cyclic nucleotide 3-phosphodiesterase (CNPase) were extremely low. These results question a chondrichthyan association of the coelacanth but are strongly in favor of an Actinistia-Tetrapoda sister group relationship, with Dipnoi being most closely related to that combined group.     

Composition of fluid from the notochordal canal of the coelacanth, Latimeria chalumnae.

Fluid from the notochordal canal of the coelacanth, Latimeria chalumnae, was analyzed for major inorganic and organic constituents and compared with blood serum from the same fish. Significantly or suggestively lower levels of sodium, magnesium, calcium, bicarbonate, sulfate, total carbohydrates, glucose, lactate, cholesterol, bound phosphate and total proteins were found in notochordal fluid than in serum, whereas potassium, chloride, urea, trimethylamine oxide, and total free amino acids were higher and inorganic phosphorus essentially identical. Osmolarity of notochordal fluid (1058 mOsm) exceeds that of serum (942 mOsm). A whitish precipitate in the fluid consisted of a matrix of fibers 100 A in diameter and of indefinite length. It resembled a sialoglycoprotein in composition and was stabilized by disulfide bonds. The fluid contained cellular debris.     

The pituitary gland of the coelacanth fish Latimeria chalumnae Smith: General structure and adenohypophysial cell types

The pituitary gland of Latimeria chalumnae is situated rostroventral to the telencephalon. The hollow pituitary stalk is bent forward and is ventrally connected to a saccus-vasculosus-like organ, rostrally to a neurointermediate lobe. The infundibular lumen protrudes far into the neurohypophysial lobules. The elongated principal part (pars cerebralis) of the pars distalis is partly embedded in a dorsal depression of the pars intermedia and caudally invaded by the neurohypophysis. It may be divided into rostral and proximal pars distalis and includes a ramified hypophysial cleft, which continues rostrally as a duct with adjacent islets of pars distalis tissue (parts of a pars buccalis). The adenohypophysis consists of cell cords and follicles. Eight tinctorial cell types can be distinguished: in the rostral islets: large basophils with acidophil globules, in the rostral pars distalis: small basophils, large basophils with amphiphil characters and erythrosin-, orange G-positive acidophils; in the proximal pars distalis: orange G-positive acidophils and small and large basophils, having similar staining properties; in the pars intermedia: one amphiphil cell type.     

LarvalAnisakis sp. (Ascaridoidea,Anisakidae) from the coelacanth,Latimeria chalumnae

A third-stage larva ofAnisakis sp. was found coiled and encapsulated on the mesentery of a 168 cm long coelacanth female (CCC no. 154) examined at Guelph in 1992. The larva was 8.4 mm in length and 300 m in maximum width. The oesophagus was 820 m and the ventriculus about 310 m in length (Fig. 1a). The prominent excretory pore was 21 m from the cephalic extremity (Fig. 1b). The tail was 105 m in length and was terminated by a minute mucron (Fig. 1c). The larva is readily identified by the asymmetrical elevations on the cephalic extremity, the prominent excretory pore and duct near the cephalic extremity and the presence of a ventriculus.