Gill morphometry of the facultative air-breathing loricariid fish,Hypostomus plecostomus (Walbaum) with,special emphasis on aquatic respiration

Gill respiratory surface area and oxygen consumption during aquatic respiration were measured in the facultative air-breathing loricariid fish,Hypostomus plecostomus. The fish did not surface to breathe atmospheric air in normoxic water; air-breathing was evoked by environmental hypoxia (water oxygen tension=35±2, mmHg) and did not show size-related threshold differences for air breathing.During gradual hypoxia, without access to atmospheric, air,H. plecostomus was found to be an oxyregulator and showed a reduced range of water oxygen tension in which the oxygen consumption remained constant in smaller fish. The critical oxygen tensions were 55 and 33 mmHg at 25°C for fish of 14–30 g and 31–80g body weight, respectively.The gill respiratory surface area (total lamellae area) is reduced, however, the lamellar frequency per mm of gill filament is high which facilitates the gas exchange. Moreover, the increase of gill respiratory surface area (b=0.666) is higher than the increase in routine VO₂ (b=0.338) showing a positive relationship between the gill respiratory surface area /VO₂ ratio and body mass (b=0.328); this indicates that the fish have greater gill respiratory surface area per unit of routine VO₂ as they grow.     

Gill disease of marine fish caused by infection with Neoparamoeba pemaquidensis

Amoebic gill disease (AGD) of maricultured salmonids, turbot, Scophthalmus maximus (L.), European seabass, Dicentrarchus labrax (L.), and sharpsnout seabream, Diplodus puntazzo (Cetti), caused by Neoparamoeba pemaquidensis has been reported from Australia (Tasmania), Ireland, France, Chile, North America (Washington State and California) and Spain. Of the salmonids, Atlantic salmon, Salmo salar L., appears to be the most susceptible with rainbow trout, Oncorhynchus mykiss (Walbaum), also suffering significant disease. Only minor outbreaks have been reported in coho, O. kisutch (Walbaum), and chinook salmon, O. tshawytscha (Walbaum). The disease now accounts for 10–20% of production costs of Atlantic salmon in Tasmania and has lead to temporary abandonment of culture of this species in parts of Spain. It is of lesser, but still significant, importance in other countries. Much is known about the pathology of AGD but the pathophysiology of the disease is poorly understood. There is evidence that non-specific immunity is involved in fish acquiring resistance to AGD, but no unequivocal evidence exists for protection as a result of specific immune responses. To date, for salmonids, the only effective treatment for AGD is a freshwater bath. Control procedures based on modification of management strategies have been minimal and virtually unresearched.     

塘堰轮捕轮放网具及其轮捕技术的研究

对塘堰鲢、鳙、草鱼的体形系数研究得出:鲢、鳙、草鱼的体长系数K_1分别为0.166,0.168和0.145;肥瘦系数K_2分别为6.36,6.40和5.50。直接采用体重公式α=K_2·G~(1/3)的计算结果来设计网具的网目大小。对所研究的三层拖刺网和革新地曳网经1984、1985两年的8个不同塘堰面积,近100网次的试验,证明它们是塘堰轮捕轮放的新型网具。     

栉孔扇贝鳃和唇瓣过氧化物酶活性

采用组织化学、电镜细胞化学和分光光度技术对栉孔扇贝(Chlamys farreri)鳃和唇瓣内的过氧化物酶(EC1.11.1.7;POD)进行研究,以探讨扇贝的鳃和唇瓣在免疫防御中的作用。组织化学显示,鳃轴、鳃丝和唇瓣上皮细胞均呈POD强阳性,结缔组织呈弱阳性;病毒感染后酶活力逐步增强。电镜细胞化学定位表明,鳃和唇瓣上皮细胞内有数量和大小不等的POD强阳性颗粒,阳性颗粒多为圆形,直径为150-220 nm;次级溶酶体也呈POD强阳性;内质网和空泡膜等细胞内膜系统以及细胞表面的微绒毛和纤毛呈POD弱阳性。结缔组织中部分血细胞呈POD强阳性。鳃轴上皮细胞内POD高电子密度阳性颗粒较少,而低电子密度阳性颗粒较多;主鳃丝上皮细胞内POD阳性颗粒较少,普通鳃丝上皮细胞内POD高电子致密阳性颗粒和呈POD强阳性的次级溶酶体均较多;唇瓣上皮细胞内POD阳性颗粒较鳃的略少。生化测定显示,鳃轴的POD酶活力最高,鳃丝次之,唇瓣最低;病毒感染24 h后,各部分的酶活力均显著增强。栉孔扇贝鳃和唇瓣内大量的POD可在抵抗病原微生物感染方面发挥重要的作用。     

Gill morphometry of the red drum,Sciaenops ocellatus

The structure and morphometry of the gills of the marine teleost, red drum, have been studied. The present analysis of gas exchange area of fish gills is one of the most intensive and the results are compared to less intense averaging methods. Based on the gill area estimates, red drum falls into the category of a fish of intermediate activity. Its gill clearly has an exchange area less than that of the tunas, but is slightly greater than that of trout or bass. The three components that contribute to total exchange area (filament length, lamellar density, and area of individual lamellae) are not all greater in species with a greater total exchange area. The best correlate is total filament length.     

The carbonic anhydrase inhibitor in trout plasma: purification and its effect on carbonic anhydrase activity and the Root effect

The plasma inhibitor of carbonic anhydrase (CA) from rainbow trout was purified using ion exchange chromatography. The inhibitor has a high isoelectric point value (pI>10). SDS-PAGE electrophoresis and gel filtration demonstrated that the inhibitor is a low molecular weight compound of about 6,000 daltons. The plasma inhibitor was more effective against gill CA than against blood CA in vitro, probably reflecting the presence of various CA-isoenzymes in red blood cells and gill tissue. The apparent Root effect, i.e., the impairment of the oxygen binding capacity of hemoglobin in red blood associated with increased blood P_{CO 2}was counteracted by the plasma inhibitor, probably by acting on membrane-bound and/or cytosolic blood CA. This interaction may be of importance in adaptive mechanisms, e.g., during the acidemic phase, when the fish is being acclimated to hypercapnic conditions.     

Effect of androgens on seawater adaptation in Arctic char,Salvelinus alpinus

Sexually immature two-year old Arctic char (Salvelinus alpinus) were implanted with Silastic capsules containing testosterone or 11-ketoandrostenedione in early spring. Seawater adaptability of the hormone-treated and sham-operated fish was tested periodically from May to August using a 48h seawater challenge test with 25‰ seawater. The sham-operated control fish displayed a seasonal pattern in seawater adaptation, showing a good hypoosmoregulatory ability until mid June followed by a marked increase in plasma sodium and magnesium levels in July and August. Gill Na⁺-K⁺-ATPase activity decreased concurrently with the observed decrease in seawater adaptability. Over the same period the androgen-treated fish displayed a similar pattern in seawater adaptability, however, in May and June the plasma sodium levels were significantly higher in both androgen-treated groups compared to the control group. Plasma magnesium regulation was impaired in both androgen-treated groups in August. Gill Na⁺-K⁺-ATPase activity in the testosterone-treated fish was lower in June compared to the control fish, whereas the activity was not affected by 11-ketoandrostenedione treatment. The results show that while androgens impair the hypoosmoregulatory capacity in Arctic char, the seasonal pattern of seawater adaptability is not affected.     

Interrelationships between gill chloride cell morphology and calcium uptake in freshwater teleosts

The involvement of the freshwater fish gill chloride cells (CCs) in trans-branchial calcium uptake (JinCa²⁺) was investigated. This was accomplished by assessing the interspecific relationships between the apical surface area of CCs exposed to the external environment and JinCa²⁺. Three species of freshwater teleosts, the rainbow trout (Oncorhynchus mykiss), the American eel (Anguilla rostrata) and the brown bullhead catfish (Ictalurus nebulosus), were used. Chronic (ten-day) treatment with cortisol in each species was used as a tool to evoke variations in both JinCa²⁺ and gill CC morphology in order to assess intraspecific relationships between CC surface area and JinCa²⁺. The results of quantitative morphometry, based on analysis of scanning electron micrographs, demonstrated that catfish possessed the lowest fractional area of exposed CC (CCFA) on the gill filament epithelium (12,744 ± 2248 m²/mm²) and was followed, in increasing order, by American eel (21,355 ± 981 m²/mm²) and rainbow trout (149,928 ± 26,545 m²/mm²). With the exception of catfish, chronic treatment with cortisol caused significant increases in CCFA owing to proliferation of CCs and/or enlargement of individual CCs (eel only). The rates of JinCa²⁺ closely reflected the CC fractional area in each species. The results of correlation analysis revealed significant correlations between CC fractional area and JinCa²⁺ in trout and eel. Owing to the absence of an effect of cortisol treatment, there was no significant correlation in catfish because of insufficient variation in CC fractional area in this species. CC fractional area was significantly correlated with JinCa²⁺ among the three species examined. These results suggest that CC is involved in calcium uptake in freshwater teleosts and that both intra- and interspecific differences in the rates of calcium uptake can be accounted for by variability in the surface area of exposed CCs on the gill epithelia.     

Studies on the effect of air exposure on gill Na+/K+-ATPase of the marble goby,Oxyeleotris marmorata,a facultative air-breathing fish

Gill and liver microsomal Na⁺/K⁺-adenosine triphosphatase (ATPase) activities, body weight, and several blood parameters were measured in marble gobies held in freshwater, in air on wet filter paper for 7 days and three days after return to freshwater following 7 days in air. During the 7 days in air, body weight, and blood Na⁺ and K⁺ concentrations remained unchanged. During the same period, however, mean specific activity of the gill ATPase fell 79% while liver ATPase specific activity was unchanged. When these fish were returned to water the specific activity of the gill ATPase returned to values seen in freshwater gobies within 3 days. Several changes were also noted in the characteristics of the ATPase in the fish held in air.     

Gross pathology and its relationship with histopathology of amoebic gill disease (AGD) in farmed Atlantic salmon, Salmo salar L

Gross pathological assessment of amoebic gill disease (AGD) is the only non-destructive, financially viable method for rapid and broad-scale disease management of farmed Atlantic salmon, Salmo salar L., in Tasmania. However, given the presumptive nature of this diagnosis, the technique has been considered questionable. This study investigated the degree of conformity between clinical signs and histological lesions observed in a commercial setting. Three groups of Atlantic salmon (n = 42, 100 and 100, respectively) were collected from various farm sites in southern Tasmania between December 2001 and April 2003. Micro-stereoscopic analysis showed that grossly affected tissue regions correspond to areas of hyperplastic lamellar fusion, generally in association with attached Neoparamoeba sp. Agreement between gross signs of AGD and histopathological diagnosis was compared. Kappa analysis indicated moderate to good agreement between methods (kappa = 0.52-0.74). Individual cases of disagreement were further scrutinized and several factors were found to influence the level of agreement between the two methods. Stage of disease development, lesions derived from other pathogens, assessor interpretation/experience, sampling methods, histological technique and/or experience were potential confounding factors. It was concluded that clinical diagnosis is acceptable as a farm-monitoring tool only. Removal of grossly affected tissue and subsequent histological examination is recommended to improve diagnostic accuracy.