Characterization of gill Na/K-ATPase activity and ouabain binding in Antarctic and New Zealand nototheniid fishes

The effects of thermal acclimation in two Nototheniid species, the stenothermal Antarctic Trematomous bernacchii and the eurythermal New Zealand Notothenia angustata, were investigated. Serum osmolality, gill Na/K-ATPase activity, sodium pump density and ouabain affinity were determined. Both fish were acclimated at their upper and lower viable thermal temperatures. Warm acclimation (+4 degrees C) of the T. bernacchii significantly decreased their serum osmolality from 550 to 450 mOsm/kg compared to cold-acclimation (-1.5 degrees C) and this was accompanied by a two-fold increase in gill Na/K-ATPase activity. Warm-acclimation (+14 degrees C) of N. angustata did not significantly change their serum osmolality from 330 mOsm/kg or gill Na/K-ATPase activity compared to the cold-acclimated (+4 degrees C) N. angustata. Using [(3)H]ouabain binding techniques, the B(max) and K(d) values of gill Na/K-ATPase enzymes were determined. No difference in the B(max) or K(d) of the warm-acclimated T. bernacchii accounted for the increase in Na/K-ATPase activity. We conclude that the change in gill Na/K-ATPase activity in the warm-acclimated T. bernacchii is not mediated by an increase in the number of enzyme sites and is not reflected in a change in ouabain affinity for Na/K-ATPase.     

Thin-blooded Antarctic fishes: a rheological comparison of the haemoglobin-free icefishes Chionodraco kathleenae and Cryodraco antarcticus with a red-blooded nototheniid, Pagothenia bernacchii

The icefishes (family Channichthyidae) comprise a unique group of teleost fishes endemic to Antarctic and sub-antarctic seas. All members of the family totally lack haemoglobin. Haematological parameters and viscosity were determined for blood from 11 specimens of two channichthyid species (Chionodraco kathleenae Regan, 1914; Cryodraco antarcticus Dollo, 1900), and 14 specimens of a red-blood Antarctic nototheniid species (Pagothenia bernacchii (Boulenger, 1902)), captured near the Italian research station at Terra Nova Bay, Ross Sea, Antarctica. Channichthyid blood contained only a small number of non-pigmented cells (10 000-40 000 cells μI^?1, depending on species) in contrast to nototheniid blood (360 000-450 000 cells μI^?1 in unstressed specimens). Blood viscosity was measured by cone plate viscometry over a range of shear rates (11.3-450s ^?1), at six temperatures between – 1.8°C and + 15°C. At the ambient Antarctic seawater temperature of – 1.8° C, and at low shear rate (22.5 s^?1), the viscosity of channichthyid blood was relatively low (3.99 ± 0.40 cP) compared with blood taken from unstressed P. bernacchii, which was about 25% more viscous (4.91 ± 0.59 cP). The viscosity of channichthyid blood was almost independent of shear rate, approximating an ideal Newtonian fluid, while the viscosity of nototheniid blood was much more dependent upon both shear rate and temperature, increasing sharply at low shear rates and low temperatures. Viscosity of nototheniid blood varied with haematocrit, which was in turn strongly influenced by stress. Blood samples taken from P. bernacchii under moderate stress induced by handling during acute caudal venepuncture had haematocrit values in the range 15–20% and viscosities of 8-l0cP, while undisturbed specimens sampled through a venous cannula yielded haematocrits of 8–10%. The viscosity of nototheniid plasma did not differ significantly from that of channichthyid whole blood or channichthyid plasma. The higher viscosity of nototheniid blood is attributable to cell content, and in stressed specimens possibly also to adrenergic swelling of erythrocytes. The absence of erythrocytes in channichthyid blood avoids the great increases in viscosity which are induced in corpusculate blood by sub-zero seawater temperatures.     

Carbohydrase activity in the digestive system of some teleost fishes.

The activity of carbohydrases in Puntius sophore (Ham.), Channa gachua (Ham.) and Cirrhinus mrigala (Ham.) has been studied. The carbohydrases have been found in the stomach, intestinal bulb, intestine, pyloric caeca and the hepato-pancreas. The hepatopancreas is the main site of production of these enzymes and it is in this organ and the intestine that their activity is highest. Their pH optimum lies between 5.4 and 6.4. The enzyme equipment in the teleost is adapted to their respective food and feeding habits both qualitatively and quantitatively. In Puntius (omnivorous) and Cirrhinus (herbivorous) all three carbohydrases, namely amylase (EC 3.2.1.1.), sucrase (EC 3.2.1.26.) and raffinase, while in Channa (carnivorous) only amylase and sucrase have been found to be active. In Cirrhinus mrigala, which is predominantly a herbivorous species, the concentration of carbohydrases is higher than those in the other two fishes.     

Morphology of the digestive system in carnivorous freshwater dourado Salminus brasiliensis

The digestive system of teleost shows remarkable functional and morphological diversity. In this study, the digestive tract and accessory organs of dourado Salminus brasiliensis are characterized using anatomical, histological, histochemical and immunohistochemical analyses. The existence of taste buds bordered by microridges in the oesophagus of dourado was recorded for the first time, thus showing that the species drives food intake by either swallowing or rejecting the food item. The Y-shaped stomach of dourado consisted of cardiac, cecal and pyloric regions with tubular gastric glands registered solely in the cardiac and cecal segments. The intestine is a short N-shaped tube with two loops, an intestinal coefficient of 0.73. The structure of pyloric caeca is similar to that of the intestine wall, comprising tunica mucosa, tela submucosa, tunica muscularis and tunica serosa layers. Histochemical analyses revealed an increased incidence of goblet cells from the midgut to the hindgut segment. A well-developed enteric plexus of scattered nerve cell and fibres are found along the digestive tract, and the calcitonin gene-related peptide (CGRP) immunoreactive neurons and fibres were identified in the myenteric plexus from the oesophagus to the hindgut. The exocrine pancreas appears diffuse in the mesentery around the stomach, intestine and also reaches the liver, and the endocrine pancreas is organized as a few islets of Langerhans. The liver comprises three distinct, asymmetric lobes, and the portal triad arrangement was registered in this tissue.     

马拉硫磷对东亚飞蝗消化道影响的形态学观察

为探讨农药马拉硫磷对东亚飞蝗Locusta migratioria manilensis(Meyen)消化系统的影响,文中以喂食形式给药,不同喂食时间点蝗虫处死后固定、石蜡包埋、连续切片、HE染色并观察蝗虫消化系统不同部位形态学的病理变化。结果表明马拉硫磷对东亚飞蝗嗉囊、前胃、胃盲囊、中肠、回肠、结肠、直肠等各消化道部位均能造成明显的形态学改变,包括内膜完整性被破坏、上皮细胞死亡、纵肌、环肌、结缔组织等病变和坏死等,且呈时间依赖性。故马拉硫磷的作用可以影响到东亚飞蝗对食物贮存、研磨、消化、养分吸收的每一个环节,最终导致蝗虫的死亡。本文研究结果对蝗虫防治研究具有重要意义。     

粉尘螨消化系统的形态学观察

光镜下观察了粉尘螨Dermatophagoides farinae消化系统结构,其组成包括：口前腔、前肠、中肠、后肠、肛门和唾液腺。口前腔由颚体围绕而成;前肠包括一个肌肉的咽和食道,食道从脑中穿过;中肠分为前中肠（包括一对盲肠）和后中肠,中肠的上皮细胞呈现多种形态; 后肠包括相对大的结肠和狭窄的直肠;消化腺为不规则形,位于脑前方。本文阐述了消化道的分支情况、显微结构及细胞形态。     

Microscopic anatomy and ultrastructure of the digestive system of three Antarctic shrimps (Crustacea: Decapoda: Caridea)

Mandibles and stomachs of three Antarctic shrimp species (Nematocarcinus lanceopes, Notocrangon antarcticus, and Chorismus antarcticus) were investigated by means of scanning electron microscopy. Transmission electron microscopy of the midgut glands was applied to find out the nutritional status of the animals, which contained a broad variety of food items in their stomachs. In contrast to the Antarctic krill, the three carideans possess a dual filter system; primary filters in the cardia and secondary filters in the pyloric chamber. Morphologically, the mandibles and stomachs of the three species vary considerably; however, their food items are similar. We conclude that stomach contents do not really reflect the different modes of life or habitat preferences of the investigated species.     

Phenotypic plasticity in the Antarctic nototheniid fish Trematomus newnesi: a guide to the identification of typical, large mouth and intermediate morphs

Trematomus newnesi is a common inshore species with a circum-Antarctic distribution. It provides the only known example of phenotypic plasticity in Antarctic notothenioid fish, existing as populations of typical, large mouth and intermediate morphs that can be difficult to identify. Using specimens from both Potter Cove, King George/25 de Mayo Island, and from McMurdo Sound, we found that the morphometric measurements gape width/head length (HL), upper jaw length/HL and, to a lesser extent, orbit diameter/HL reliably separated the morphs. For use in a key, we converted the ratios into the qualitative characters head shape, head width and upper jaw length relative to middle of the eye. To increase the reliability of the key, we also assessed intra-morph variability in these characters. The key is supplemented with colour photographs illustrating the distinctive features for separation of the morphs. We discovered that, in the case of the specimens from Potter Cove, each morph had a distinct pattern of colouration: typical—trunk blotched, with yellow or orange-brown predominating especially on pectoral and caudal fins; large mouth—trunk blotched, with green predominating especially in pectoral and opercular regions; and intermediate—trunk less blotched, with homogeneous dark brown-grey on trunk, pectoral and caudal fins. We also discuss the ecological implications of colour in the morphs.     

Aminotripeptidase (EC E.4.1.3) activity in the digestive system of some teleost fishes.

Aminotripeptidase (EC 3.4.1.3) has been found to be present in the intestinal mucosa, hepatopancreas and the pyloric caeca of the three fished examined. The pH optimum of the enzyme ranges from 6.6 to 7.6. The pH optimum varies from species to species and also from section to section of the gut in the same species. The enzyme is most active in the carnivorous Channa gachua in comparison to the other fishes studied.     

A difference in optomotor behaviour of two Antarctic nototheniid fishes is correlated with the presence of a choroid<Emphasis Type="Italic"> rete mirabile</Emphasis> and Root effect

The hypothesis that fish vision is influenced by the presence of a choroid rete mirabile (an oxygen-concentrating apparatus in the eye) and the Root effect was tested using the optomotor response in two nototheniid species from Antarctica. Pagothenia borchgrevinki, an active cryopelagic zooplanktivore, does not exhibit a major Root effect and the rete is absent. In contrast, the sluggish, benthic nototheniid, Trematomus bernacchii, possesses both a rete and a significant Root effect. Whole-eye ocular PO2 was higher in T. bernacchii (18.6 kPa) than in P. borchgrevinki (18.1 kPa) and the optomotor response of T. bernacchii was positively influenced by subtended angle on a moving background whereas P. borchgrevinki did not respond to any subtended angle (0–600 min of arc). The optomotor response of T. bernacchii may therefore have been facilitated by elevated ocular PO2 due to the presence of the choroid rete and the Root effect.     

Morphology of the anterior digestive system of tonnoideans (Gastropoda: Caenogastropoda) with an emphasis on the foregut glands

ABSTRACT

Tonnoideans are marine carnivorous caenogastropods that prey on different invertebrates, namely polychaetes, sipunculids, bivalve and gastropod molluscs, and echinoderms. The morphology of the digestive system of 20 species from five families of the Tonnoidea was examined (for most of these species for the first time), and the salivary glands of six of them were studied using serial histological sections. Most of the studied families are rather similar anatomically, except Personidae (Distorsio), which differs both in proboscis morphology and the structure of the salivary glands. In most tonnoideans the salivary glands are split morphologically and functionally into anterior and posterior lobes, the latter synthesising strong sulfuric acid. The ducts of the posterior lobes are lined with non-ciliated epithelium and receive usually paired ciliated ducts from the anterior lobes to form a non-ciliated common duct, opening into the buccal cavity. In Personidae, the salivary glands are not separated into lobes, but are instead composed of ramifying tubules that are histologically different in the proximal and distal parts. Radulae of Tonnoidea are rather variable, with different patterns of interlocking teeth, both in the transverse and longitudinal rows, which may be related to particular feeding mechanisms. Due to the peculiarities of Personidae, the close relationship between that family and the rest of the Tonnoidea is questioned.     

A falsification of the thermal specialization paradigm: compensation for elevated temperatures in Antarctic fishes

Specialization to a particular environment is one of the main factors used to explain species distributions. Antarctic fishes are often cited as a classic example to illustrate the specialization process and are regarded as the archetypal stenotherms. Here we show that the Antarctic fish Pagothenia borchgrevinki has retained the capacity to compensate for chronic temperature change. By displaying astounding plasticity in cardiovascular response and metabolic control, the fishes maintained locomotory performance at elevated temperatures. Our falsification of the specialization paradigm indicates that the effect of climate change on species distribution and extinction may be overestimated by current models of global warming.     

Storage and absorption in the digestive system of carnivorous and herbivorous prickleback fishes (Teleostei: Stichaeidae): ontogenetic, dietary, and phylogenetic effects

The effects of ontogeny, diet, and phylogeny on glycogen storage levels and esterase and alkaline phosphatase activities in four related prickleback fishes were determined in situ using quantitative histochemistry. Of these species, Cebidichthys violaceus and Xiphister mucosus shift from carnivory to herbivory at approximately 45 mm standard length (SL), whereas Xiphister atropurpureus and Anoplarchus purpurescens remain carnivores. Comparisons between small (30-40 mm SL) and larger (60-75 mm SL) wild-caught juveniles showed that glycogen storage levels and alkaline phosphatase activity were unchanged with ontogeny. Comparisons between the larger wild-caught juveniles and juveniles of the same size that had been raised on a high-protein animal diet revealed that glycogen storage level and alkaline phosphatase activity increased in all species in response to this diet. Esterase activity also increased in response to the high-protein animal diet in all four species but increased with ontogeny only in C. violaceus, X. mucosus, and X. atropurpureus, in the xiphisterine clade, and not in A. purpurescens, in the adjacent alectriine clade. Xiphister mucosus and X. atropurpureus showed indistinguishable responses in esterase activity to ontogeny and diet despite their divergent natural diets. Overall, glycogen storage level and alkaline phosphatase activity responded primarily to diet, whereas esterase activity was also influenced by ontogeny and phylogeny and differed between intestinal regions among the species.     

Contribution of sea ice organic matter in the diet of Antarctic fishes: a diatom-specific highly branched isoprenoid approach

New sets of diatom-specific biomarkers, highly branched isoprenoids (HBIs), have been recently proposed to trace carbon flow from ice algae and pelagic phytoplankton to higher trophic level organisms. In the Antarctic, diene, a HBI of sea ice origin was more abundant in ice-associated species, while triene, a HBI of phytoplanktonic origin, was more abundant in pelagic species. However, this HBI approach has never been applied on Antarctic benthic species. Here, we analyzed diene and triene in the liver and the muscle of eight Antarctic coastal fish species (108 specimens). HBI lipids were detected in all specimens, confirming the contribution of sea ice and pelagic organic matter in coastal benthic fish species. Moreover, HBI markers were much more concentrated in the liver than in white muscle, and the relative concentrations of diene and triene strongly varied among species, as a probable result of species differences in feeding habits and trophic ecology. Seasonal variations in HBI concentrations were detected during the whole year in white muscle, but not in the liver. These findings are consistent with the well-known spring bloom in November–December, just before the annual ice break up, and the second proliferation of ice algae during the land-fast ice formation, in April–May. Therefore, investigation of HBI lipids in white muscle will likely shed new light on seasonal changes in the contribution of ice algal-derived organic matter in higher trophic level organisms.     

Projecting mechanics into morphospace: disparity in the feeding system of labrid fishes

In no group of organisms has the link between species richness, morphological disparity, disparity in mechanics and functional or ecological diversification been made explicit. As a step towards integrating these measures of diversity, we examine how the mechanics of the anterior-jaw four-bar linkages of 104 species of Great Barrier Reef (GBR) labrid fishes maps into a scale-independent morphospace. As predicted from theory, no relationship exists between overall size and the mechanics of velocity and force transmission in labrid anterior-jaw linkages. Nonetheless, mechanics associated with the anterior jaw appear to have constrained diversification of labrid anterior-jaw morphology. Furthermore, simulations depict a generally nonlinear relationship between the length of individual links and transmission of motion. In addition, no relationship was found between morphological disparity and mechanical disparity among the most species-rich labrid groups from the GBR. It is also established that regions of morphospace equivalent in morphological disparity differ over nearly an order of magnitude in mechanical disparity. These results illustrate that without an explicit interpretation of the consequences of per unit change in morphology, conclusions about diversification drawn only from morphological disparity may be misleading.