Efficacy of Netminder® silicone release coating for biofouling reduction in bay scallop grow‐out and comparative effects on scallop survival,growth and reproduction

Netminder^®, a water‐based silicone barrier release coating, was highly effective in reducing biofouling of lantern nets during grow‐out/overwintering of bay scallops, Argopecten irradians irradians, in a large‐scale restoration programme in New York, USA. Compared with untreated nets, scallops held in Netminder^®‐coated nets experienced reduced survival after 8 months, probably due to higher loads of epibionts on their shells. However, this was countered by higher reproductive and overall condition of scallops in treated vs. untreated nets; there were no consistent differences in shell growth in different net treatments. Although further testing is recommended under a wider range of conditions, we conclude that for the purposes of our scallop restoration work, coating nets with Netminder^® would eliminate the need for a gear change in spring, thus reducing labour costs; the coating process should be refined so that Velcro closures of nets do not become sealed shut.     

Protection conferred against viral nervous necrosis by simultaneous inoculation of aquabirnavirus and inactivated betanodavirus in the sevenband grouper, Epinephelus septemfasciatus (Thunberg)

An aquabirnavirus (ABV) and a formalin-inactivated betanodavirus [redspotted grouper nervous necrosis virus (RGNNV)] were investigated for their potential to prevent RGNNV-induced viral nervous necrosis (VNN) in the sevenband grouper, Epinephelus septemfasciatus (Thunberg). Three groups of fish were injected intramuscularly with ABV, intraperitoneally with inactivated RGNNV (iRGNNV) or with both ABV and iRGNNV. At 3, 7, 14, 21 and 28 days post-injection (p.i.), fish were challenged by intramuscular injection of RGNNV. Control fish, which received neither ABV nor iRGNNV, showed high mortalities in all RGNNV challenges. Fish that received only ABV exhibited relative percent survival (RPS) of >60 against RGNNV challenges at 3, 7, 14 and 21 days p.i., but not at 28 days p.i., while fish that received only iRGNNV showed significantly higher protection against RGNNV challenges only at 21 and 28 days p.i. In contrast, fish that received both ABV and iRGNNV showed 60 or higher RPS against all RGNNV challenges. Fish inoculated with iRGNNV with or without ABV exhibited similar high titres of neutralizing antibodies to RGNNV at 14, 21 and 28 days p.i. These results indicate that combined inoculation with iRGNNV and ABV conferred both rapid non-specific and delayed specific protection against VNN.     

A new viral epizootic of Anguilla japonica Temminck and Schlegel

Abstract. In 1969, a new kind of epizootic occurred among eels in Japan and virological investigation was initiated. A new virus designated eel virus european (EVE) was isolated and biological, cytological, serological tests and infectivity trials were carried out. In its CPE on RTG-2 cells and additionally in its biological properties and particle size, EVE was found to be similar to infectious pancreatic necrosis virus (IPNV). Serologically, EVE was similar to the ď Honnincthun, France, strain of IPNV. However, infectivity trials showed that EVE and IPNV differed; EVE killed Japanese eels Anguilla japonica but not rainbow trout fry Salmo gairdneri , while IPN virus killed rainbow trout fry but not eels. We consider EVE to be the primary agent causing the new epizootic and propose the name viral kidney disease for the resulting clinical condition.     

Food consumption and digestive enzyme activity of Clarias batrachus exposed to various temperatures

The effect of temperature on the food consumption rate and the digestive enzyme activities of Clarias batrachus (80.60 ± 5.34 g) were evaluated. Fish were exposed to six different temperatures of 10, 15, 20, 25, 30 and 35 °C following an acclimation temperature of 25 °C. The rate of temperature change was 2 °C day^?1. Highest food consumption was recorded at 25 °C. It gradually reduced with decreasing water temperature. Food consumption rate was significantly (P < 0.05) lower at 10 °C compared with other treatments. Hence, 46.67, 8.20–23.58 and 1.02–6.15% reduced food consumptions were recorded in groups exposed at 10, 15 and 20 °C temperatures, respectively, compared with the 25 °C. The consumption rate was not affected in fish exposed at 30 and 35 °C. Total protease, trypsin and chymotrypsin activities were significantly (P < 0.05) higher in fish exposed at 25 °C compared with others. Lipase activity was significantly (P < 0.05) higher in fish exposed at 30 °C compared with others. Lowest enzyme activities were recorded at 10 °C. Water temperature below 25 °C affected the food consumption and digestive enzyme activities in fish that served as indicators of stress in fish.     

Dietary phosphorus requirement of juvenile Atlantic salmon, Salmo salar L.

The objective of this study was to determine the dietary phosphorus (P) requirement of juvenile Atlantic salmon, Salmon salar L. Triplicate groups of fish (mean initial weight 1.4 g) were fed semipurified, casein-gelatine-based diets containing one of five levels of P (4, 8, 10, 15 and 25 g kg⁻¹) from Ca(H₂PO₄)₂·H₂O, or a commercial feed (17 g kg⁻¹ P) for 9 weeks. Weight gains did not differ significantly among treatment groups fed the experimental diets but were slightly less than gains in fish fed the commercial feed. Feed efficiency (wet weight gain/dry feed consumed) was similar in all groups, averaging 1.45. Availability of dietary P, estimated from apparent retention and apparent digestibility, was 86%. Whole-body P concentrations declined in fish fed diets containing less than 10 g kg⁻¹ P. Fitting a logistic curve to dietary P vs. whole-body P concentrations indicated that a minimum of 11 g kg⁻¹ dietary P (9 g kg⁻¹ digestible P) was required by juvenile Atlantic salmon to maintain whole-body P concentrations at initial levels. Calculation of a dietary requirement using a simple factorial model which incorporated measurements of P availability, feed efficiency and normal whole-body P concentration indicated that the dietary requirement was approximately 10 g kg⁻¹. The dietary requirement established in this study (10–11 g kg⁻¹) is higher than previously reported for Atlantic salmon or other fishes. Possible reasons for the wide range of reported dietary P requirements in fishes are discussed.     

Are cell redox or lactate dehydrogenase kinetics responsible for the absence of gluconeogenesis from lactate in sea raven,hepatocytes?

Previous studies have reported very low rates of gluconeogenesis from lactate in sea raven (Hemitripterus americanus) hepatocytes compared to other teleosts studied. This study examines whether hepatic cell redox or lactate dehydrogenase (LDH) characteristics may explain this observation. Sea raven hepatic optimal LDH activities (pyruvate reductase direction) were more than 40 times less compared with rainbow trout liver values (40 vs 1914 μmol·min⁻¹·g⁻¹ protein). The Km(lactate) was 9.24 and 0.86 mM for sea raven and trout hepatic LDH, but the Km(pyruvate) was similar between the two species (0.11 and 0.21 mM, respectively). These results suggested that sea raven liver LDH did not favour lactate use and was more indicative of the mammalian M-isozyme. Gel electrophoresis showed a predominant intermediate isozyme, with a small amount of the M-type LDH. Phosphoenolpyruvate carboxykinase (PEPCK) was localized to the mitochondrial compartment, while there was no apparent mitochondrial glutamate-oxaloacetate transaminase (GOT) activity. No in vitro lactate flux to glucose was found in untreated, 10 mM ethanol-treated, or 3 mM NH₄Cl-treated sea raven hepatocytes, although CO₂ production from lactate was decreased by ethanol and increased by NH₄Cl. These results provide evidence that cell redox does not limit gluconeogenesis from lactate, while low activities and the kinetic characteristics of LDH may partially explain the low lactate gluconeogenesis reported in sea raven hepatocytes. To whom correspondence should be addressed at University of Ottawa.     

Molecular evidence for the lack of transmission of the monogenean Sparicotyle chrysophrii (Monogenea, Polyopisthocotylea) and isopod Ceratothoa oestroides (Crustacea, Cymothoidae) between wild bogue (Boops boops) and cage-reared sea bream (Sparus aurata) and sea bass (Dicentrarchus labrax)

In the Mediterranean area, wild fish have often been suggested as either the reservoirs of the causative agents or at least the carriers of the pathogens responsible for disease outbreaks in cultured fish. However, no epidemiological investigations on actual pathogen/disease interactions between farmed and wild fish have been conducted even for the most important fish pathogens. Only sporadic isolations and identifications of various pathogens in wild fish have been done and real associations with the pathological conditions that exist within the farm environment and vice versa have not been established. Monogenean ectoparasite Sparicotyle chrysophrii and isopod Ceratothoa oestroides are commonly found in the Mediterranean cage-reared sea bream and sea bass and in the surrounding wild fish population. Both species were recognized as pathogens that seasonally inflict serious losses in fingerlings and juveniles of sea bream and sea bass, being potentially propagated and exchanged during wild and caged fish interaction. In order to evaluate the degree of pathogens transfer between wild and farmed fish, we investigated genetic population structures of these two important parasitic pathogens inferred by mtDNA cytochrome oxidase I locus. Parasites isolated from wild and farmed fish on the two most productive Adriatic fish farms showed genetic heterogeneity, contradicting widely accepted hypothesis of cross-contamination, at least in case of S. chrysophrii and C. oestroides. As far as we know, this is the first report that in a study of pathogen transfer molecular evidence was employed to asses the genetic population structure of shared parasites.     

Cloning and expression of a surface immunogenic protein in Streptococcus dysgalactiae isolated from fish and its application in enzyme‐linked immunosorbent assays to diagnose S. dysgalactiae infections in fish

Lancefield group C Streptococcus dysgalactiae (GCSD) causes severe necrotic lesions in the caudal peduncle in the genus Seriola farmed in Japan. To develop a sero‐diagnostic method for GCSD infection in farmed fish, we attempted to identify a surface immunogenic protein that induces an antibody after infection with GCSD by immunoblot analysis using sera collected from infected fish. A protein obtained from sodium dodecyl sulfate (SDS) extracts of GCSD was identified as S. dysgalactiae surface immunogenic protein (Sd‐Sip). Sd‐Sip exhibited more than 94% homology with a surface antigen or a hypothetical protein from S. dysgalactiae mammalian isolates at the nucleotide sequence level. Expression of the recombinant Sd‐Sip (rSd‐Sip) was confirmed by immunoblot analysis, that is, its reactivity to GCSD‐infected sera. Antibody detection ELISA using rSd‐Sip and their usefulness for diagnosis of GCSD infection were examined. GCSD‐infected sera collected from farmed amberjack, Seriola dumerili (Risso), showed strong reaction with immobilized rSd‐Sip. Meanwhile, sera immunized by other pathogenic bacteria of fish were showed ELISA values similar to those of non‐infected sera. These results of this study suggest that the antibody detection ELISA using rSd‐Sip is an effective diagnostic method for GCSD infection in fish.