Comparative Biochemistry and Physiology Part A: Physiology最新文献

There is lack of information concerning species diversification in the Non-Antarctic Nototheniid fish both in relation with their variation in organismal performance and in the morphofunctional characteristics underlying this variation. This work was designed to study in three Sub-Antarctic Nototheniids, Eleginops maclovmus, Patagonotothen tessellata, and Paranotothenia magellanica, cardiocirculatory features that may reflect interspecific differences in organismal performance, which in turn may explain aspects of evolutionary and ecological diversity.

Haematocrit values were similar in all three species (between 28 and 32), being in the range of that observed in other red-blooded Notothenioids. In all species, the heart ventricle was fully trabeculated (Type I ventricle) with P. tessellata and P. magellanica having higher relative ventricle weights than E. maclovinus. The latter species was characterized by unique spindle-shaped ventricle, apparently caused by the insertion of a pair of respiratory muscles on either side of the pericardial cavity. Intrinsic cardiac performance was assessed using an in vitro isolated and perfused heart preparation working under loading conditions. Common trends in the three species were a) the intrinsic heart rate higher than that shown by the Antarctic counterparts, b) stroke volume positively related to preload and inversely to afterload, c) pressure work exhibiting higher cost (in terms of oxygen consumption) than volume work, and d) higher mechanical efficiency under volume loading than under pressure loading. There were clearly defined interspecific differences in cardiac mechanical performance between the two Nototheniinae and E. maclovinus. The heart of the latter differed from those of the Nototheniinae, particularly in its incapacity to maintain constant stroke volume and cardiac output under pressure loading. This finding may be relevant for evaluating organismal performance in light of Notothenioid diversification.

Living free of the substrate and possessing distinctive morphology, Pleuragramma antarcticum is an atypical nototheniid. Cladistic analyses indicate that Pleuragramma is one of the most phyletically derived species in the family. It is also distinctive in a number of features of its biology. I comment on phylogenetic and developmental aspects of these morphological and physiological features in Pleuragramma: skeleton and notochord, extent of red muscle, lipid storage, blood, retina, lateral line, brain and gastrointestianal system. An entire suite of characters is unique to Pleuragramma, but individual features are convergent within other nototheniid clades living in the water column. Osteology provides the best documented evidence that paedomorphosis has been important in the evolution of Pleuragramma.

Fermentability of dietary cellulose, sodium alginate, chitin, α-starch and kaolin (non-fermentable control) by gut microbes was compared in a tilapia, Oreochromis niloticus, fed a diet containing one of the above supplements (150 g · kg⁻¹) for 14 days. The thickness of the tunica muscularis was also compared among fish fed these diets. The concentration of short-chain fatty acids (SCFA) in gut contents was higher in fish fed the α-starch than in fish fed the sodium alginate, chitin, or kaolin diets. Intestinal contents from fish fed the kaolin (control) diet were incubated in batch culture with each of the other supplements. The volume of released gas and production of SCFA for 24 hr was greater with a α-starch as a substrate than in those with the other substrates. The thickness of the tunica muscularis differed among dietary groups but villus height did not. Fish fed chitin or α-starch had a thicker tunica muscularis than those fed cellulose or sodium alginate. These results suggest that this detritivorous fish digests α-starch to produce SCFA in the intestine by microbial fermentation.

The mackerel icefish (Champsocephalus gunnari) is a prominent member of the coastal fish fauna of the Seasonal Pack-Ice Zone and the islands north of it. Separated into a number of stocks, its distribution ranges from the Scotia Arc region, namely South Georgia, in the Atlantic Ocean sector to the Kerguelen-Heard Plateau in the Indian Ocean sector. Mackerel icefish have been heavily exploited since the beginning of the 1970s with reported annual catches exceeding 50–100,000 tonnes in some years. C. gunnari has many characteristics typical of Antarctic fish species with respect to life history characteristics, such as egg size, fecundity and growth. These fall well within the range of other sympatric red-blooded notothenioids; eggs are large and yolky. Egg diameter, egg production per gram body weight and growth performance at South Georgia and the Kerguelen Islands was comparable with similar-sized nototheniids and channichthyids. Stocks of C. gunnari have a number of biological characteristics in common, such as feeding mode and food, early life history and growth in the first years of life. However, stocks in sub-Antarctic waters differ in reproductive characteristics, such as length and age at first spawning, natural mortality and life expectancy from those on more southerly grounds. They may grow to more than 60 cm and may become 13–15 yrs old. However, in the vicinity of South Georgia and the Kerguelen Islands, fish apparently do not exhaust this growth potential fully. Their ability to reproduce at an early age coupled with a comparatively high fecundity and growth performance may mean stocks of C. gunnari in sub-antarctic waters have far more resilience and a greater capacity to rebuild than species with the slower reproductive rates common in other notothenioids.

Studies of the hemoglobin system of fish of the suborder Notothenioidei have been extended to non-Antarctic species Pseudaphritis urvillii and Notothenia angustata. The two species belong to families that were the first to diverge within the suborder. The degree of amino acid sequence identity with Antarctic notothenioids and other non-Antarctic fish species is analyzed with respect to phyletic and ecological divergence.

Nitric oxide synthase-positive nerve cells have been found in most vertebrate classes and also some invertebrates, indicating an early evolutionary origin for the enzyme and its function as a neurotransmitter. The general distribution and inhibitory effect on motility of nitric oxide in the fish gut agrees well with studies from other vertebrates, but details may vary between species, suggesting variations in function. The coexistence with vasoactive intestinal polypeptide (VIP)/pituitary adenylate cyclase-activating polypeptide (PACAP) suggests a co-function in fish as in mammals, but this remains to be confirmed.

Standard metabolic rate and evaporative water loss were measured for three species of small goanna (Varanus caudolineatus, V. brevicauda and V. eremius). Four general patterns of gas exchange are associated with often extended periods of no gas exchange, which presumably are non-ventilatory periods. Extended periods of no gas exchange continued for as long as 137 min at 14°C, 37 min at 20°C and 28 min at 25°C. These extended non-ventilatory periods have two important implications. First, when measuring Vo_2std, it is important to recognize these non-ventilatory periods and not include them in the period for determining standard metabolic rate or else ensure that any non-ventilatory periods are accompanied by an “oxygen deficit payback” period. Second, the extended non-ventilatory period enables the partitioning of cutaneous and respiratory standard evaporative water loss. Pulmonary evaporative water loss, expressed as a percentage of total evaporative water loss, was found to be very low: 4.7%, 2.4% and 5.9% at 14, 20 and 25°C, respectively.