The influence of high oral doses of mercuric chloride on organ toxicant concentrations and histopathology in rainbow trout,Oncorhynchus mykiss

1. Trout were fed a pellet diet for 42 d contaminated with mercuric chloride to provide a mercury concentration of 10 g metal/kg dry weight of food.2. Sloughing of the gut epithelium and food regurgitation occurred in the last 3 weeks of the study, but no mortalities were observed.3. The kidney showed increased numbers of melano-macrophages, but gill pathology was notably absent.4. Mercury accumulated in the gill, liver, kidney, muscle and mucus. The highest toxicant concentrations were recorded in the gill and liver, while contamination in the muscle was lower than most tissues examined.5. Fish excreted mercury via the body surface mucus, a previously unknown route of mercury clearance. Mucus mercury content correlated positively with whole body burdens, suggesting mucus toxicant levels may be used to identify mercury contamination in live fish.     

Histochemical observations on the salmonids Salmo salar L. and Salmo trutta L. and the ephemeropterans Baetis rhodani (Pict.) and Ecdyonurus venosus (Fabr.) following a simulated episode of acidity in an upland stream

Salmonids (Salmo salar, Salmo trutta) and mayflies (Baetis rhodani, Ecdyonurus venosus) which had been exposed to simulated episodes of low pH, and low pH with elevated aluminium, were examined histochemically for the presence of aluminium and mucus. The control fish and mayflies and those exposed to low pH did not stain for aluminium, although increased mucus production was demonstrated in fish gills. Trout and salmon exposed to aluminium at low pH exhibited extensive aluminium and mucus coating of the secondary gill lamellae. No mucus was produced by mayflies but aluminium was apparent on all parts of the body. Mean aluminium concentrations of digested fish gills were 2950 and 3050 g g^–1 dry wt. for trout and salmon respectively, whilst for whole specimens of B. rhodani and E. venosus values were 1 200 and 3 175 g g^–1 dry wt.     

Haematological and histological changes in fish Heteropneustes fossilis exposed to pesticides from industrial waste water

The present study investigated the potential changes in hematologic parameters and histology of fish Heteropneustes fossilis when exposed to industrial waste water of different concentrations. The toxicant enter into the fish body from different rout, inhalation, dermal oral, and other several rout for entering in the fish body. The blood parameters of fish H. fossilis control group and treatment were investigated on 1st, 5th, 10th, and 20th days of experiment, hematologic variation was observed in RBC, WBC, MCV, MCH, and MCHC count. Histopathologic changes in liver, intestine, gill, muscle, and heart showed increasing degrees of damage in the tissues in correlation with the accumulation pattern of pesticides, while liver, intestine, gill, muscle, and heart of control group exhibited a normal architecture. Toxic effects of pesticides vary in different organs of the fish H. fossilis significant. The fish exposed to higher concentration showed uncoordinated alterations in behavioral responses, especially erratic and jerky swimming, physiologic, malformation, histologic, hematologic and biochemical changes, frequent surfacing and in gulping, mucus secretion, an increase in opercular movement, and copious secretion of mucus of all over the body.     

In vitro evidence for the ionoregulatory role of rainbow trout mucus in acid, acid/aluminium and zinc toxicity

Rainbow trout body mucus dialysed with acidified distilled water at pH 7,5 and 3 experienced ion depletion which was greatest at pH 3 and minimal between pH 7 and 5. Mucus Na⁺ loss is exacerbated in the presence of 1 mg I⁻¹ aluminium as A1₂(SO₄), at pH 5 and 7. Al₂(SO₄), causes greater depletion of Na⁺ from mucus than A1C1₃. A lethal level of zinc (2 mg 1⁻¹) does not deplete mucus Na⁻ or K⁺, unlike a lethal level of aluminium (1 mg 1⁻¹) at pH 7. The results are discussed in terms of the ionoregulatory role of mucus in heavy metal and acid toxicity.     

Oral L-cysteine ethyl ester (LCEE) reduces amoebic gill disease (AGD) in Atlantic salmon Salmo salar

There is a need for the development of alternative therapeutic treatments for amoebic gill disease (AGD) in Atlantic salmon Salmo salar L. to maintain the sustainability of the Tasmanian Atlantic salmon aquaculture industry. This study aimed to assess the effects of the mucolytic drug L-cysteine ethyl ester (LCEE) on marine Atlantic salmon mucus and whether or not it may have a therapeutic advantage for the alleviation of AGD when administered orally. We also aimed to document any physiological consequences of LCEE. Results showed that LCEE significantly decreased the viscosity of marine Atlantic salmon mucus both in vitro, where LCEE concentration showed a negative relationship to mucus viscosity (R2 = 0.95 at 11.5 s(-1)), and in vivo. Oral administration of LCEE at 52.7 mg LCEE kg(-1) fish d(-1) over 2 wk significantly delayed the progression of AGD-associated pathology during an aggressive, cohabitation induced, laboratory infection. Medicated fish had approximately 50% less gill filaments affected by AGD than control fed fish at 3 d post-infection when assessed using histology. Palatability of medicated feed was shown to be approximately 65% of control feed. No osmoregulatory disturbance was seen in medicated fish, although blood and whole body flux data indicated a slight acidosis coinciding with an increased plasma total ammonia concentration. However, both variables were within a tolerable physiological range and returned to control levels 3 d post-cessation of medicated feed. LCEE holds potential as an in-feed additive when administered over 2 wk prior to infection to delay the progression of AGD associated pathology. From the parameters measured, LCEE seems to have minimal physiological consequences after 2 wk of administration.     

Biochemical responses of fish exposed to a harmful dinoflagellate Cochlodinium polykrikoides

To elucidate the ichthyotoxic mechanisms of a harmful dinoflagellate Cochlodinium polykrikoides, biochemical responses of fish exposed to blooms were investigated. Particularly, based on our finding that oxidative damages of gill were associated with fish mortality (J. Plankton Res. 21 (1999) 2105-2115), dysfunction of ion-transporting enzymes and secretion of gill mucus of fish exposed to this bloom species were examined. The susceptibilities of several fishes to C. polykrikoides were different; the active pelagic fishes such as black scraper Thamnaconus septentrionalis, red sea bream Pagrus major, beakperch Oplegnathus fasciatus and seaperch Malakichthys wakiyae, were more vulnerable than the benthic fishes, flounder Paralichthys olivaceus and rockfish Sebastes inermis. In addition, the higher the algal cell density, the higher the fish mortality. When the test fishes were exposed to C. polykrikoides of 5000 cells ml(-1), the transport-related enzymes, carbonic anhydrase and Na(+)/K(+)-ATPase activities were significantly decreased. The activity of carbonic anhydrase was decreased with increasing algal cell density and exposure time. The quantity of total polysaccharide in gill mucus is higher in the fish exposed to C. polykrikoides than in the control fish; the magnitudes were higher in the pelagic fishes than that of benthic fishes. Moreover, a drop of blood pH and oxygen partial pressure (pO(2)) was also observed in red sea bream and flounder subjected to C. polykrikoides. These results suggest that the inactivation of gill transport-related enzymes activities, the fall in blood pO(2) and abnormal secretion of gill mucus by the C. polykrikoides may be one of the principal causes of fish kill.     

Free radical production by the red tide alga, Chattonella antiqua.

Summary The red tide alga,Chattonella antiqua, was found to show a strong chemiluminescence, using luminol as the reagent, when exposed to ultraviolet irradiation. This luminescence was completely inhibited by ascorbate or catalase, suggesting that hydrogen peroxide was generated by the plankton. Red tide cells exposed to fish gill mucus from young yellowtail resulted in the release of a large number of mucocysts and a weak luminosity, and showed a strong reduction of cytochromec in the medium. Therefore, the discharge of mucocysts from the red tide, induced by the presence of gill mucus, may be accompanied by the release of active oxygen species. The active oxygen may be involved in depolymerization of mucus glycoproteins from the gill lamellae.     

金鱼(Carassius auratus)鳃对颗粒吸附态铅的吸收

研究了金鱼（Ｃａｒａｓｓｉｕｓ ａｕｒａｔｕｓ）鳃在悬浮水铝矿吸附态Ｐｂ暴露实验中对Ｐｂ吸收过程,结果表明,在保持水中游离态Ｐｂ浓度不变（０．１ｍｇ．Ｌ＾－１）、吸附态Ｐｂ浓度增加的条件下,鳃中Ｐｂ,Ａｌ浓度均随暴露浓度增加而增加,血液中Ｐｂ浓度随鳃中Ｐｂ浓度的增加率（直线斜率０．１７１）低于溶解态Ｐｂ、暴露实验的增加率（直线斜率０．３４３）,附着鳃上的部分Ｐｂ未移转至血液中,鳃中Ｐｂ／Ａｌ比较水     

Morphological, histochemical and immunohistochemical study of the gill epithelium in the abyssal teleost fish Coelorhynchus coelorhynchus

Histochemical and immunohistochemical study was carried out on nitrinergic innervation and neuroendocrine system in the gill epithelium of the abyssal fish Coelorhynchus coelorhynchus. The results showed that nNOS-positive nerve fibers, originating from the branchial arch were present in the subepithelial tissue of branchial primary filament. nNOS-positive neuroendocrine cells were also present in the primary filaments and secondary lamellae. Numerous mucous cells in the gill epithelium were AB/PAS-positive, while sialic acid was absent as confirmed by neuraminidase reaction and WGA lectin histochemistry. The mucus compounds in abyssal teleost fish are different from those found in pelagic species, being related to their living conditions. In abyssal species, greater numbers of chloride and neuroendocrine cells are involved in the movement of water and electrolytes. Neuroendocrine cells possess oxygen receptors which mediate the cardiovascular and ventilatory response to oxygen deficiency, as reported in teleost species. Besides, NO contributes through nervous stimulation to the regulation of vascular tone and blood circulation in the gill.     

Studies on the fish-gill microclimate: interactions between gill tissue,mucus and water-quality

Synopsis Single gill filaments, isolated from carp and exposed to flowing water, produced mucous layers that filled the spaces between secondary lamellae. Filaments, removed from fish acclimated to either tap water or to ion-poor water, were exposed either to acclimation water or to acidified acclimation water with added aluminium. Ion-selective microelectrodes and 3 M KCl electrodes were used to measure conditions at the filament surface and within the filament's efferent filament artery. Isolated filaments maintained a constant transepithelial potential difference but internal pH and sodium concentration were less stable in some water qualities. Surface accessibility for microciimate analysis, however, was excellent. Small gradients of Na⁺ and more substantial gradients of pH were found in ion-poor water and in acidified water qualities, respectively. Mucus is thought to contribute to these gradients by providing an unstirred layer between gill tissue and external water. The filament microclimate was only slightly dependent on the ion-exchange properties of mucus and these were only marginally and unpredictably influenced by water quality.     

The relationship between nitrogen output and changes in mucous cell function in the amphibious teleost Blennius pholis L. during aerial exposure

The numbers of mucous cells in the epidermis of the head and body and in the surface of the gill arch of the amphibious blenny, Blennius pholis L., were estimated on fish immersed in sea water and after 4 h aerial exposure. During emersion there appeared to be a considerable reduction in the frequency of epithelial mucous cells in the areas studied, although counts for the head epidermis were somewhat variable. A concomitant decline in the number of cells thought to be actively secreting was also recorded in tissue samples from both the head and gills, while in the body epidermis the potential for mucus-secretion was maintained close to the levels observed in immersed fish.
Histochemical studies revealed epidermal mucous cells containing either sialylated acid mucopolysaccharides or neutral mucins, or a mixture of these, in both the head and the body, whereas in the gill arch epithelia there were, in addition, cells containing sulphated acid mucopolysaccharides. After emersion, a disproportionate loss of cells containing neutral and sialylated mucus from the gill epithelia resulted in an increase in the proportion of secreting cells staining positively for sulphated acid mucopolysaccharides.
The results of this study are discussed in relation to nitrogenous excretion during aerial exposure.     

Changes in the electrophoretic profiles of gill mucus proteases of the eastern oyster Crassostrea virginica in response to infection by the turbellarian Urastoma cyprinae

Urastoma cyprinae occurs on the gills of various bivalves species, including the eastern oyster Crassostrea virginica. While the worm is known to cause severe gill disruption in mussels, no evidence of this nature has been described for oysters. Nonetheless, high levels of U. cyprinae have been reported in oysters, which may, in turn, reduce the oyster's overall condition. U. cyprinae is strongly attracted to oyster gill mucus, which is suggested to play an active role in the worm's feeding activities. Furthermore, host mucus contains many active components, including proteases, which have been suggested to play a defensive role against invading organisms. It follows, therefore, that some of the interactions between U. cyprinae and oysters take place in host gill mucus. Studies were undertaken to determine whether the presence of U. cyprinae altered the electrophoretic profiles of oyster gill mucus, using proteases as indicators. Findings reveal that oyster gill mucus contains three proteases, a putative acid protease at 96 kDa, a zinc metalloprotease at 64 kDa, and a serine protease at 33 kDa. Results based on experiments using mucus preparations extracted from infected and noninfected oysters, along with those using lyophilized mucus incubated with live U. cyprinae, confirm that the presence of U. cyprinae alters the protease composition of gill mucus. The present data demonstrate that both U. cyprinae and host gill mucus actively secrete proteases. While the precise roles of these enzymes still need to be defined, one of their functions may be associated with digestion-related activities induced by the worm.     

Cleaner fish, Labroides dimidiatus, diet preferences for different types of mucus and parasitic gnathiid isopods

Cleaner fish, Labroides dimidiatus, prefer the mucus of the parrotfish, Chlorurus sordidus, to parasitic gnathiid isopods, the main items in their diet, indicating a major conflict between clients and cleaners over what the latter should eat during interactions. We tested whether the conflict varied with client species (and the quality of its mucus) and with the presence of blood in the gnathiids. First, we offered cleaners the choice between mucus of the parrotfish and that of the snapper, Lutjanus fulviflamma. When offered equal amounts of mucus on Plexiglas plates, cleaners readily developed a significant preference for the parrotfish mucus. Reducing the amount of parrotfish mucus by 75% made the preference disappear. In a second test, we offered the cleaners gnathiids that were or were not engorged with client fish blood. Cleaners showed no significant preference for either food item. Our results suggest that the degree of conflict between cleaners and clients may vary between species, depending on whether the latter have a preferred mucus. In contrast, the cleaners' lack of preference for engorged gnathiids benefits clients because it means that cleaners do not hesitate to eat unengorged gnathiids before the gnathiids harm the fish by removing blood or by transmitting blood parasites.     

Epidemic trichodinosis associated with severe epidermal hyperplasia in largemouth bass, Micropterus salmoides, from North Carolina, USA

An epidemic of trichodinosis associated with severe epidermal hyperplasia occurred in adult largemouth bass (Micropterus salmoides) from the Chowan River drainage, North Carolina (USA) in late winter to early spring 2002. Initial reports by anglers of fish with a "jelly-like slime coat" on the skin prompted an electrofishing survey in which about 10% of sampled largemouth bass had a very thick, bluish-white "mucoid layer" on the body and fins. Moderate to heavy infestations of the ciliate Trichodina were detected in wet mounts of skin from five of five fish having the mucoid layer; these fish also had significant gill infestations. An additional two fish with only mild reddening and four asymptomatic fish (no skin lesions) had mild skin infestations but no gill infestations. Two asymptomatic fish had no skin parasites. Four fish with the mucoid layer were necropsied and had extremely severe epidermal hyperplasia on the body and fins. The hyperplasic epidermis had relatively few mucus cells and typically was about 5-10 times thicker than healthy epidermis. The upper four fifths of the epidermis consisted of finely vacuolated, highly flattened, somewhat disorganized epithelial cells. No other significant clinical or histopathologic abnormalities were detected. No systemic infection by pathogenic bacteria was noted. The environmental cause of the epidemic is uncertain but the lesions suggest that some chronic stressor was involved.     

Non-lethal detection of DNA from Cichlidogyrus spp. (Monogenea, Ancyrocephalinae) in gill mucus of the Nile tilapia Oreochromis niloticus

Infection of Nile tilapia Oreochromis niloticus by monogeneans of the genus Cichlidogyrus is harmful. Currently, diagnosis of this infection is based on invasive techniques and the identification of isolated parasites by their morphology. To facilitate diagnosis, we have developed a non-lethal polymerase chain reaction (PCR) test for detection of Cichlidogyrus spp. DNA in the gill mucus of O. niloticus, using 5 pairs of specific primers based on Cichlidogyrus sclerosus 28S rRNA (Cicly 1 to Cicly 5) which generate fragments of approximately 188, 180, 150, 159 and 189 bp, respectively. PCR specificity was tested using genomic DNA extracted individually from 175 isolated Cichlidogyrus spp., 75 Gyrodactylus cichlidarum and 75 endopararasitic Enterogyrus spp., as well as from 75 protozoans Trichodina spp. The Cicly primers were used to detect Cichlidogyrus spp. DNA in mucus from the gills of 23 Nile tilapia confirmed to be infected with the parasite. Negative controls consisted of 45 uninfected Nile tilapia. The limit of sensitivity of the assay was 1.2 ng of purified parasite DNA. The Cicly primers did not amplify DNA from the mucus of non-infected Nile tilapia, G. cichlidarum, Trichodina spp. or Enterogyrus spp. In all cases, the sensitivity and specificity of the test were 100%. The sequences of all the amplified fragments showed a high similarity to that of the 28S rRNA region of C. sclerosus (93 to 100% identical to GenBank Accession No. DQ157660.1). We provide evidence for a safe and non-invasive DNA-based diagnostic method for the presence of Cichlidogyrus in the gill mucus of O. niloticus.     

The viscosity and glycoprotein biochemistry of salmonid mucus varies with species,salinity and the presence of amoebic gill disease

Fish mucus has previously been reported to change in appearance and composition among species and in response to changes in salinity and disease status. This study reports on the mucus viscosity and glycoprotein biochemistry of Atlantic salmon (Salmo salar L.), brown trout (Salmo trutta L.) and rainbow trout (Oncorhynchus mykiss Walbaum) in freshwater and seawater, both naïve to and affected by amoebic gill disease (AGD). Cutaneous mucus viscosity was measured over a range of shear rates (11.5, 23, 46 and 115 s^–1), and non-Newtonian behaviour was demonstrated for all three species. Mucus viscosity was significantly greater in seawater than in freshwater for all species, and significantly lower in AGD-affected Atlantic salmon and brown trout. Mucus glucose, total protein and osmolality data indicated that differences in viscosity due to salinity were mostly attributed to changes in mucus hydration, while differences due to disease were mostly attributed to changes in mucus composition. Trends in gill mucus cell histochemistry included shifts in glycoproteins from neutral mucins in freshwater to acidic mucins in seawater, and shifts towards neutral mucins, with an increase in mucus cell numbers, in response to AGD. Results suggested that Atlantic salmon and brown trout are more similar to one another in their mucus profile than to rainbow trout. Atlantic salmon and brown trout both exhibited a whole-body mucus response to AGD, whereas rainbow trout exhibited only a local gill response. Findings hold implications for fish physiology and pathology, and indicate that future fish-disease management strategies should be species and condition specific.Communicated by I.D. HumeThe word mucus has been used in its noun form throughout the paper for clarity

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An erratum to this article can be found at .     

The occurrence, distribution and pathology associated with gnathiid isopod larvae infecting the epaulette shark, Hemiscyllium ocellatum

Gnathiid isopod praniza larvae were found to infect the epaulette shark Hemiscyllium ocellatum. All sharks carried larvae on their external body surface, with the preferred attachment site in both sexes around the cloaca (P<0.05). The claspers were the second site of preference in male sharks. Within the buccal and branchial cavities, about 16% of larvae were attached to the roof and floor of the mouth and 84% attached to the gills. A significant positive correlation existed between larval number and fish size. Histological examination showed that larval attachment in the buccal cavity elicited variable responses, the most severe being a loss of epithelium and compression of underlying tissue. No host cellular response or tissue proliferation was observed. Praniza attached preferentially to the efferent side of gill filaments (relative to blood flow), and caused loss of epithelium, compression of tissue, and a small amount of connective tissue proliferation. Attachment to the gill septum or to the afferent side of the gill filament caused lamellar disruption, a cellular inflammatory response, and connective tissue proliferation. Scanning electron microscopy showed little obvious praniza-induced gill damage, other than localised tissue distortion to form "pockets" around larvae attached between filaments. The results suggest that praniza larvae do not cause sufficient tissue damage to adversely affect the health of this shark species.     

Water balance trumps ion balance for early marine survival of juvenile pink salmon (Oncorhynchus gorbuscha)

Smolting salmonids typically require weeks to months of physiological preparation in freshwater (FW) before entering seawater (SW). Remarkably, pink salmon (Oncorhynchus gorbuscha) enter SW directly following yolk absorption and gravel emergence at a size of 0.2 g. To survive this exceptional SW migration, pink salmon were hypothesized to develop hypo-osmoregulatory abilities prior to yolk absorption and emergence. To test this, alevins (pre-yolk absorption) and fry (post-yolk absorption) were transferred from FW in darkness to SW under simulated natural photoperiod (SNP). Ionoregulatory status was assessed at 0, 1 and 5 days post-transfer. SW alevins showed no evidence of hypo-osmoregulation, marked by significant water loss and no increase in gill Na?/K?-ATPase (NKA) activity or Na?:K?:2Cl? cotransporter (NKCC) immunoreactive (IR) cell frequency. Conversely, fry maintained water balance, upregulated gill NKA activity by 50 %, increased the NKA α1b/α1a mRNA expression ratio by sixfold and increased NKCC IR cell frequency. We also provide the first evidence of photoperiod-triggered smoltification in pink salmon, as fry exposed to SNP in FW exhibited preparatory changes in gill NKA activity and α1 subunit expression similar to fry exposed to SNP in SW. Interestingly, fry incurred larger increases in whole body Na? than alevins following both SW and FW + SNP exposure (40 and 20 % in fry vs. 0 % in alevins). The ability to incur and tolerate large ion loads may underlie a novel mechanism for maintaining water balance in SW prior to completing hypo-osmoregulatory development. We propose that pink salmon represent a new form of anadromy termed "precocious anadromy".     

鱼体(去鳃)和鱼鳃对不同形态铜的积累特征

在实验室条件下研究实验鱼Ｐａｒａｃｈｅｉｒｏｄｏｎ对人工河水中不同形态的积累特征,对比了鱼体（去鳃）和鱼鳃对铜吸收量的差异,并探讨了鱼对铜的吸收机理。研究结果表明,实验鱼鳃部和体内铜积累量均随水相游离铜浓度增高,暴露时间增长而增加,但鳃部积累浓度较鱼体其余部分高一个数量级,其从水相富集铜的速率显著高于鱼体。     

Estimation of conditional stability constant for copper binding to fish gill surface with consideration of chemistry of the fish gill microenvironment

Binding-site concentration and conditional stability constants for copper and fish gill surface interactions were calculated based on the data from the literature. Six scenarios were modeled by including or excluding pH and alkalinity differences between the fish gill microenvironment and the bulk solution and the presence of free mucus in the calculation. We demonstrate that changes in pH or alkalinity, or both, for model input had only a slight influence on the calculated results because of the small difference in pH and alkalinity between the gill microenvironment and the bulk solution under the specific experimental conditions. Inclusion of free mucus in the model, however, led to a large change in the final results. For example, with consideration of free mucus and changes in pH and alkalinity in the model, the calculated site concentration and the stability constant were 0.022 micromol/g wet tissue and log K=8.77, respectively, compared to 0.026 micromol/g wet tissue with log K=7.78 without free mucus and pH/alkalinity change.