Determination of feeding mode in fishes: the importance of using structural and functional feeding studies in conjunction with gut analysis in a selective zooplanktivore Chirostoma estor estor Jordan 1880

Anatomical and histological studies of the endangered atherinid Chirostoma estor estor reveal that the species is ideally adapted to feeding on zooplankton. It has a superior protractile mouth with short unicuspid mandibular teeth. The buccal cavity is a highly adapted branchial sieve with branchial spines which develop in complexity with age to form a continuous flexible interdigitated mat. The filter bed has many of the characteristics of a cross-flow filter, which is ideal for a continuously feeding and filtering animal as the filter bed will not readily become occluded. The aggregates from the cross-flow filter pass to the rear of the buccal cavity where they are triturated by well-developed pharyngeal teeth. The species has a short intestine (<0·3 × body length) with no histological evidence of stomach-like structures, no pyloric caecae and with trypsin-like enzymes operating at high pH. Feeding trials with natural plankton showed a sequence of particle size selection as the animals grow, with older animals taking cladocerans up to 700 μm in diameter. Although some adults occasionally take small fish prey, cumulatively, the present studies indicate that the fish is a zooplankton feeder throughout all its life stages.     

Trophic polymorphism, habitat and diet segregation in Percichthys trucha (Pisces: Percichthyidae) in the Andes

Divergent natural selection affecting specific trait combinations that lead to greater efficiency in resource exploitation is believed to be a major mechanism leading to trophic polymorphism and adaptive radiation. We present evidence of trophic polymorphism involving two benthic morphs within Percichthys trucha , a fish endemic to temperate South America. In a series of lakes located in the southern Andes, we found two morphs of P. trucha that could be distinguished on the basis of gill raker length and five other morphological measures, most of which are likely associated with the use of food resources. The differences were consistent across all lakes examined, and were correlated with habitat use and diet. Individuals with longer gill rakers were more abundant in the littoral zone (littoral morph) while the short gill-raker morph was more abundant at 10 m depth and deeper (deep benthic morph). Both morphs fed primarily on benthic invertebrates, but the littoral morph fed more on larval Anisoptera than did the deep benthic morph. Phenotypic correlations among traits were high for the littoral morph, but low and non-significant for the deep-benthic morph. We suggest that gill raker length may influence the relative efficiency of suction feeding for the two morphs. This is the first evidence of trophic polymorphism in fishes from temperate South America.     

Active NaCl absorption across split lamellae of posterior gills of Chinese crabs (Eriocheir sinensis) adapted to different salinities

Split lamellae of posterior gills of Eriocheir sinensis adapted to fresh water, brackish waters (9 or 18‰) or seawater (36‰) were mounted in Ussing chambers, and transepithelial short-circuit currents and conductances were measured with salines, containing approximately in vivo-like NaCl concentrations. Active sodium and chloride absorption (I_Na and I_Cl), the transcellular conductances and the leak conductance were identified with external amiloride and/or DIDS. Split gill lamellae of crabs adapted to fresh water displayed similar magnitudes of I_Na and I_Cl with 10 mmol l⁻¹ NaCl in the external medium (internally haemolymph-like NaCl saline). Augmenting external NaCl (50 mmol l⁻¹) resulted in an increase of I_Cl, whereas I_Na decreased. Split gill lamellae of crabs adapted to brackish waters (external NaCl of 125 and 225 mmol l⁻¹, respectively) showed lower currents than preparations of freshwater crabs (50 mmol l⁻¹ external NaCl). With split gill lamellae of seawater crabs no currents were detected (450 mmol l⁻¹ NaCl on both sides). The transcellular conductances showed similar changes as the currents. The leak conductance of split gill lamellae of crabs adapted to fresh or brackish waters was low (0.3–0.8 mS cm⁻²), whereas it was much higher (7 mS cm⁻²) with preparations of seawater crabs.     

官亭水库黄尾鲴食性的初步研究

黄尾鲴仔幼鱼阶段的食性是随着鳃耙和肠管形态的变化而变化。体长11.8—12.3mm,鳃耙形状开始分化,肠呈1—2弯曲,仔鱼吞食小型枝角类,主要是裸腹溞;体长15.8—17.4mm,口端位,鳃耙成筛网,肠呈4—8弯曲,前肠膨大,主要食物是腐屑,摇蚊幼虫,“水华”型的裸藻与蓝绿藻。体长18mm的幼鱼,口下位,鳃耙与肠管进一步发育,幼鱼转入底栖,其前肠内含物主要为泥沙、腐屑、摇蚊幼虫,浮游动物与浮游植物。黄尾鲴成鱼的主要食物为大量的腐屑和极少数的着生硅藻、颤藻。成鱼食物营养价值很差,其总N含量为0.372%,有机质为4.8%,每克湿重的热值为146.35卡,成鱼周年摄食,摄食量大,这是黄尾鲴摄食的特点。       

Cortisol stress response and histopathological alteration index in Clarias gariepinus exposed to sublethal concentrations of Qua Iboe crude oil and rig wash

The histological effect on and stress response of post juvenile Clarias gariepinus exposed to Qua Iboe crude oil and rig wash were investigated. Fish weighing 60–90 g and measuring 16–18 cm were exposed for 7–28 days to 8.00 ml^?1 Qua Iboe crude oil and 0.0018 ml^–1 rig wash, both being 0.1 of the 96 hr LC₅₀. Blood samples of C. gariepinus were collected every seven days and evaluated for stress by measuring cortisol concentration. The gills and liver were studied and scored for Gill Alteration Index (GAI) and Hepatic Alteration Index (HAI), respectively. There was an increase in cortisol level up to the 7th and 14th day among the group exposed to Qua Iboe crude oil, with a decrease on the 21st and 28th day. The rig wash group increased in cortisol level up to the 7th day and decreased slightly on the 14th day, after which the trend became irregular. The toxic effects of the Qua Iboe crude oil and rig wash were time dependent, as shown by the histopathological alteration index (HAI) of gill and liver. After 28 days of exposure, the gills had irreparable damage due to high frequency of cellular necrosis and degeneration, whereas the liver had from moderate to severe damage due to the high frequency of cellular degeneration and inflammation. Qua Iboe crude oil and rig wash are both toxic to C. gariepinus, therefore their indiscriminate discharge to the environment must be discouraged.     

Neoparamoeba pemaquidensis引起的海水鱼阿米巴鳃病

海水养殖的鲑鱼及鲽鱼(Scophthalmusmaximus)的阿米巴鳃病是由Neoparamoebapemaquidensis引起的。在西班牙,该病对鲑鱼的海水养殖造成巨大损失,同时也正威胁着鲽鱼的养殖。组织病理损伤主要是鱼鳃上皮细胞的增生和肥大。该虫仅寄生在鱼鳃表面。现已有证据证明,非特异免疫参与鱼类抵御该病,但还没有证明特异性免疫在此过程中发挥作用的相似证据。对鲑鱼来说,治疗该病惟一有效的方法就是用淡水浸泡     

Light and Electron Microscopy of the Spore of Myxobolus heckelii n. sp. (Myxozoa), Parasite from the Brazilian Fish Centromochlus heckelii (Teleostei, Auchenipteridae)

ABSTRACT. A myxosporean parasitizing the gill filaments of the freshwater teleost fish Centromochlus heckelii collected in the Tocantins River (Lower Amazonian Region, Brazil) is described using light and electron microscopy. This parasite produces spherical to ellipsoidal cyst-like plasmodia up to 250 μm in diameter, with a thick wall strengthened by several stratified juxtaposed crossed collagen layers, whose thickness varies according to the number of the layers. Several compressed fibroblasts are observed among the collagen fibrils. Deposits of spherical dense material are scattered at the internal periphery of the cysts. Plasmodia and different developmental stages, including immature and mature spores, filled the central region of the cysts. The spore body is ellipsoidal in valvar view and biconvex in sutural view. It is formed by two equal-sized and symmetric valves measuring 12.7 μm long (12.2–13.1) ( n =50), 6.6 μm wide (6.3–6.9) ( n =25), and 4.0 μm (3.7–4.4) ( n =20) thick. A thin layer formed by fine and anastomosed microfibrils is observed at the spore surface. Two equal, elongated pyriform polar capsules measure 2.9 μm (2.7–3.3) × 1.7 μm (1.4–2.0) ( n =25), each containing four or five oblique polar filament coils. The binucleated sporoplasm contains numerous spherical sporoplasmosomes, glycogen particles, and a large vacuole with fine granular matrix. Based on the morphological and ultrastructural differences and specificity of the host, we describe this isolate as a new myxosporidian, Myxobolus heckelii n. sp. (Myxozoa, Myxosporea).     

Testing the stages model in the adaptive radiation of cichlid fishes in East African Lake Tanganyika

Adaptive radiation (AR) is a key process in the origin of organismal diversity. However, the evolution of trait disparity in connection with ecological specialization is still poorly understood. Available models for vertebrate ARs predict that diversification occurs in the form of temporal stages driven by different selective forces. Here, we investigate the AR of cichlid fishes in East African Lake Tanganyika and use macroevolutionary model fitting to evaluate whether diversification happened in temporal stages. Six trait complexes, for which we also provide evidence of their adaptiveness, are analysed with comparative methods: body shape, pharyngeal jaw shape, gill raker traits, gut length, brain weight and body coloration. Overall, we do not find strong evidence for the ‘stages model’ of AR. However, our results suggest that trophic traits diversify earlier than traits implicated in macrohabitat adaptation and that sexual communication traits (i.e. coloration) diversify late in the radiation.     

New records of fish parasitic isopods of the gill-attaching genus Mothocya Costa,in Hope, 1851 from the Virgin Islands,Caribbean, with description of a new species

Two species of Mothocya Costa, in Hope, 1851 are reported from the Virgin Islands. Mothocya xenobranchia Bruce, 1986 was collected from St. John Island from the gills of the Atlantic needlefish, Strongylura marina, which is a new locality record and also confirms a previously uncertain host identity. Mothocya bertlucy sp. n. is described from St. Thomas, St John and Guana Islands, from the gills of the redlip blenny, Ophioblennius macclurei, the first record of a blenny as host for any Mothocya. The distinguishing characters of Mothocya bertlucy sp. n. include its small size (< 9 mm) and eyes, the slender pleotelson with a narrowly rounded caudomedial point, extended uropod peduncle and uropods which do not extend past the pleotelson posterior margin, and the narrow pleon which is only slightly overlapped by pereonite 7.