In light of the relationship of lungfish to the origin of tetrapods, information on the respiratory biology of lungfish can give insight into the functional morphological and physiological prerequisites for the conquest of land by the first tetrapods. Stereological methods were employed in order to determine the respiratory surface area and thickness of the water-blood barrier or air-blood of the gills, lungs, and skin, respectively, of the South American lungfish Lepidosiren paradoxa. The morphometric diffusing capacity was then determined by multiplying by the appropriate Krogh diffusion constants (K). Our results indicate a total diffusing capacity of all respiratory organs of 0.11 mL min(-1) mmHg(-1) kg(-1), which is more than twice the value of the physiological diffusion capacity (approximately 0.04 mL min(-1) mmHg(-1) kg(-1)). Of this, 99.15% lies in the lungs, 0.85% in the skin, and only 0.0013% in the gills. Since K for CO(2) is 20-25 times greater than for O(2), diffusing capacity of CO(2) through the skin is potentially important. That of the gills, however, is negligible, raising the question as to their function. Our results indicate that the morphological prerequisites for terrestrial survival with regard to supporting aerobic metabolism already existed in the lungfish.
ABSTRACT. FEEDING ANO MORPHOLOGIC RELATIONS Wlm mE DIGESTIVE TRACT Of "CURIMBATÁ", PROCHlLODUS LlNEATUS(VALENCIENNES) (OSTEICHmYES. PROCHILODON. TIOAE), Of A PONO IN Soum BRAZIL. Some aspects of the feeding habits and the morphology of the digestive tracts of Prochilodus Iineatus (Osteichthyes, Prochilodontidae) are investigated in Lagoa Dourada, Ponta Grossa, Paraná. A total of 102 specimens were captured between April1993 and April 1994. From each specimen, the following measurements were determined: total and standard length, weight, sex, length of abdominal cavity. Histological and anatomical analyses were performed on the buccal cavity, pharynx, stomach, and intestine. P. /ineatus is a ilyophagous species with short and numerous incisiform teeth attached to the lips and no pharyngeal teeth.The gill rakers are thick, oblique, and laminate. This species has a "u" -ceacal -type of muscular stomach, with well developed mucosal folds. The submucosa of the pyloric region is composed of dense connective tissue and the muscular layer is well developed which characterize a gizzard-type. The intestine is greatly coiled occupying nearly ali the abdominal cavity. The folds ofthe anterior region are circular and valvar lobulated in the medium and posterior regions. KEY WORDS. Osteichthyes, Prochilodus lineatus, feeding habits, digestive tract morphology Os peixes estão adaptados para se alimentar de um determinado item, ou conjunto de itens. A composição do alimento consumido provê informações sobre o nicho que as espécies ocupam em seu habitat (NIKOLSKY 1963).Para FUGI & HAHN (1991) a plasticidade na dieta de peixes obedece a certo limite pré-estabelecido pela forma do tubo digestivo, cujas estruturas podem refletir as tendências alimentares da espécie.
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