The involvement of Aeromonas salmonicida virulence factors in bacterial translocation across the rainbow trout, Oncorhynchus mykiss (Walbaum), intestine

The pathogenic bacterium Aeromonas salmonicida is the causative agent of furunculosis, a lethal disease in salmonids. The mode of lateral transmission has not been conclusively defined, but A. salmonicida is able to translocate across the intestinal epithelium of salmonids, making the intestinal route a probable candidate. This study investigated some of the virulence mechanisms used by the bacteria to promote translocation. Intestinal segments were placed in modified Ussing chambers to investigate epithelial functions during exposure to bacterial factors. The factors were: extracellular products (ECP), lipopolysaccharide (LPS) or live or heat-inactivated A. salmonicida. Fluorescein isothiocynate (FITC)-labelling enabled detection of translocated bacteria by fluorometry. Live A. salmonicida translocated to a greater degree than heat-inactivated bacteria, suggesting that the bacteria utilize a heat sensitive surface-bound virulence factor which promotes translocation. The epithelium was negatively affected by ECP, manifested as decreased net ion transport, indicating a disturbance in ion channels or cell metabolism. LPS did not affect the epithelium in vitro when administered on the luminal side of the intestinal segment, but significantly increased epithelial translocation of fluorescent bacterial-sized microspheres when administered on the serosal side. This is suggested to be caused by increased transcellular transport, as the paracellular permeability was unaffected indicating maintained epithelial integrity.     

Can the mudskipper,Periophthalmus chrysospilos,tolerate acute environmental hypoxic exposure?

The mudskipper P. chrysospilos became inert at 0.76 μl O₂.ml⁻¹ when it was allowed to respire in a ‘closed respiratory chamber’. No ethanol was detected although it excreted three times more total carbon dioxide into the surrounding sea water than the amount of oxygen consumed. However, P. chrysospilos could survive environmental hypoxic exposure (0.8 μl O₂.ml⁻¹) for at least 6 h. Upon normoxic recovery, the oxygen debt repayment was only a small fraction of the oxygen deficit incurred during the 6 h of hypoxic exposure. It would therefore appear that P. chrysospilos was able to cope with environmental hypoxia by suppressing its metabolic rate.     

Cytochemical characterization of peripheral blood cell populations of two Cyprinidae,Carassius auratus and Ctenopharyngodon idellus

Fish are the most diverse species of all vertebrate groups, and their blood cells have shown variable characteristics in terms of morphology. Cytochemical staining for enzyme activity in blood leukocytes will help assess the immune function of fish. We characterize blood cells from crucian carp (Carassius auratus) and grass carp (Ctenopharyngodon idellus) by using a Diff‐Quick stain as well as different cytochemical methods. Blood specimens obtained from crucian carp and grass carp were evaluated after cytochemical staining for acid phosphatase (ACP), alkaline phosphatase (ALP), naphthol AS chloroacetate esterase (AS‐DNCE), naphthyl acetate esterase (NAE), α‐naphthyl butyrate esterase (NBE), peroxidase (MPO) and periodic acid–Schiff's reaction (PAS) using commercial kits. Blood cell types were evaluated based on their morphological characteristics and the presence or absence of specific chromogen. The expression pattern of enzymes was similar between the two Cyprinidae and was also broadly consistent with other fish species. However, there were some interesting differences detected between crucian carp and grass carp, including naphthol AS chloroacetate esterase activity in monocytes, peroxidase activity and location in thrombocytes. The ACP, ALP and MPO expressions of different leukocytes of the two Cyprinidae were evaluated by Image Pro Plus and were analysed for statistical significant differences. This investigation provides basic haematology and enzyme activity analyses for crucian carp and grass carp and serves as an approach to evaluating the immune response of fish.     

Multiple passage of infectious salmon anaemia virus in rainbow trout,Oncorhynchus mykiss (Walbaum), did not induce increased virus load

The infectious salmon anaemia virus (ISAV) has not been observed to cause natural disease in farmed rainbow trout, Onchorhynchus mykiss (Walbaum), but may cause high mortality in farmed Atlantic salmon, Salmo salar L. In this study, ISAV was passaged 10 times in succession by intraperitoneal injections of serum from previous passage into naïve rainbow trout. The serum viraemia was monitored by real‐time qPCR. The rainbow trout in this study became infected but did not develop ISA. No clinical signs were observed in the rainbow trout in any passage, but replication of ISAV was detected from Day 4 post‐infection (p.i.). Neither increased relative virus loads nor histopathological and immunohistochemical findings consistent with ISA were observed. However, the expression of interferon type I and Mx genes were slightly up‐regulated in the hearts of some individual fish at day 17 p.i. Sequencing of all open reading frames in the ISAV genome of the 10th passage revealed two nucleotide mutations, one in segment 6 coding for the haemagglutinin–esterase (HE) and one in segment 1 coding for the basic polymerase 2 (PB2). The mutation in HE resulted in an amino acid substitution T/K₃₁₂.     

Vascular actions of neurohypophysial peptides in the flounder

Free swimming, chronically cannulated flounder have been used to study the blood pressure effects of arginine vasotocin (AVT) and isotocin. The initial fall in dorsal aortic blood pressure following AVT injection coincided with an increase in ventral aortic blood pressure, suggesting AVT caused constriction of the arterio-arterial pathway. Ventral aortic blood pressure increased in a dose dependent manner with increasing AVT dose. Dorsal aortic blood pressure also increased following the initial fall but not in a dose dependent manner, the effect at higher doses being off set by branchial vasoconstriction. Isotocin also caused dorsal aortic blood pressure to fall due to branchial vasoconstriction, but no subsequent pressor effect was seen. Branchial vasoconstriction caused by both teleost neurohypophysial peptides suggests the presence of neurohypophysial peptide receptor(s) in the gill, although it is unclear as to whether this is a single common receptor or different populations for each peptide. The dorsal aortic pressor effect of AVT and its absence following isotocin injection suggests there may be other types of neurohypophysial receptors in post-branchial vascular beds. The vascular actions of AVT and isotocin suggest that these peptides may play some role in the regulation of blood pressure or regional blood flow distribution.     

黑脊倒刺鲃性腺早期分化的研究

对黑脊倒刺鲃(Spinibarbus caldwelli)早期性腺分化的过程进行了显微和亚显微研究。结果显示:在5日龄仔鱼中,观察到生殖嵴出现;在28日龄稚鱼中,观察到精巢的早期分化;在32日幼鱼中,观察到明显分化;而直到42日龄幼鱼中,才观察到早期卵巢的早期分化;在90日龄幼鱼中,观察到明显分化。结果表明,黑脊倒刺鲃的精巢分化要明显早于卵巢的分化。     

First account of the metazoan parasite fauna of oilfish Ruvettus pretiosus Cocco, 1829 (Perciformes: Gempylidae) in South African waters

Parasites are an important but neglected component of ecosystems that can be used as indicators of host biology and ecology. In the present study, the metazoan parasite assemblage of Ruvettus pretiosus, an understudied but widely distributed predatory gempylid, caught off South Africa was surveyed. A total of seven parasite taxa, including four new infection records (Bolbosoma capitatum, Rhadinorhynchus sp., Hepatoxylon trichiuri and Anisakis sp.), two new locality records (B. capitatum and Rhipidocotyle sp.) as well as the ectoparasitic copepod Sagum foliaceus and the cestode Tentacularia coryphaenae were recovered from the eight specimens examined.     

Accumulation of waterborne selenium by rainbow trout (Salmo gairdneri), eggs,fry and juveniles

The effect of waterborne selenite levels on selenium accumulated by different developmental stages of rainbow trout (Salmo gairdneri) was studied using⁷⁵SeO ₃ ⁼ as a tracer. All stages readily accumulated selenium at both high and low concentrations, but the rate of accumulation increased as the trout developed from the egg to the juvenile feeding stage. The low rate of selenium accumulation by embryos seemed to be related more to a lack of gills than to the presence of a chorion. The bioconcentration factor (the ratio of tissue-to-water concentrations) declined in all groups with increased waterborne selenium levels; accumulation rates appeared limited by cell permeability. At low levels of waterborne selenium (0.4μg/l), the total accumulated was small relative to existing body burdens and unlikely to contribute significantly to the nutritional requirement for selenium. High levels (45.6μg/l), however, caused considerable selenium accumulation and may be sufficient to overcome the effects of low dietary selenium.     

Thyroid hormone concentrations in the gonads of wild chum salmon during maturation

Changes in gonadal and plasma concentrations of thyroid hormones were examined at various stages of maturation in chum salmon (Oncorhynchus keta) caught in the Bering Sea and the Bay of Alaska. Plasma concentrations of thyroxine (T₄) were less than 5 ng ml⁻¹, and those of 3,5,3′-triiodo-L-thyroxine (T₃) were less than 2 ng ml⁻¹ I in both males and females, regardless of the degree of sexual maturity or the gonadosomatic index (GSI). There was no clear relationships between circulating thyroid hormone levels and tissue levels. The ovarian T₄ concentrations were undetectable (less than 0.2 ng g⁻¹) or less than 2 ng g⁻¹ when GSI was lower than 1%, but increased thereafter and reached a plateau of 8–10 ng g⁻¹ when GSI became 2%. The ovarian T₃ concentrations were about 5 ng g⁻¹ when GSI was 1%, increased to a maximum level (20 ng g⁻¹) when GSI was about 2%, and decreased to a constant level of 10 ng g⁻¹ thereafter. The T₄ and T₃ content in single oocyte increased proportionally to the oocyte volume, indicating a constant incorporation of the hormones into the oocyte. The T₄ concentrations in the testis were 1 ng g⁻¹ or less regardless of the GS1. On the other hand, the T₃ concentrations were highest (15 ng g⁻¹) when the GSI was less than 1%, decreased thereafter when spermatocytes appeared in the testis, and became about 5 ng g⁻¹ I in testes containing spermatozoa, raising the possibility of a role for T₃ during early gamete and/or gonad maturation of testes.     

Regulation of the interrenal of fishes: non-classical control mechanisms

The regulation of the interrenal of teleostean fishes is reviewed from the perspective of non-classical control mechanisms and new evidence is presented suggesting gonadotropic control of the interrenal. Cortisol secretion by the interrenal, in addition to regulation by ACTH, appears to be mediated by other hormones. Physiologically relevant, direct control of interrenal function by hydromineral factors is unclear.In vitro experiments with interrenals of coho salmon (Oncorhynchus kisutch) indicate that salmon gonadotropin is extremely corticotropic and both ACTH and gonadotropin stimulate the secretion of large quantities of androstenedione from the interrenal.