Interspecific comparison of experimental and natural routes of Lepeophtheirus salmonis and Caligus elongatus challenge and consequences for distribution of chalimus on salmonids and therapeutant screening

Although the gills have been reported as a site for settlement by sea lice attached stages in experimental challenges, the prevalence and abundance of infection on gills have not been reported in farmed fish and have been reported only rarely in wild salmonids. Disproportionate attachment to the gills may be significant in evaluation of new therapeutants and this study asks whether the efficacy data from studies of therapeutants based on experimental challenge can be extrapolated to the fish farm arena. The distribution of chalimus on gills, body and fins of farmed first sea year Atlantic salmon were examined in two Scottish sea lochs, each on two occasions (30 fish on each sampling date), fish from one farm with infection with Lepeophtheirus salmonis only and the other farm with exclusively Caligus elongatus. The dorsal fin was the primary attachment site of L. salmonis (50% and 33% in two samples respectively) with 29% and 32% on other fins and 20% and 29% on the body and head. Only one of 56 chalimus (1.8%) and four of 75 chalimus (5.3%) were attached to the gills. In contrast, the chalimus distribution of C. elongatus was predominantly on fins other than the dorsal, including the tail, 74% and 71%, on two sampling occasions, respectively, with only 4.2% and 3.6% of chalimus located on the dorsal fin. The pectoral fins were the most common location with 32%, followed by the tail 23%, pelvic fins 14% and only 3% on the anal fin. None of 287 and 111 chalimus in two samples, respectively, of C. elongatus was attached to the gills. The low abundance of lice on the gills indicated that non‐destructive sampling methods adequately represented lice infection. In three experimental challenges with L. salmonis, the gills were a major attachment location with 19.9–36.3% of chalimus, 9.9–26.9% on the body, 22–27% on the dorsal fin and 19–23% on the other fins. These differences with natural challenge in L. salmonis reported here and also in the literature suggest that the importance of the gills for chalimus location in the experimental model is atypical and an artefact of reduced host swimming speed in tanks that permits copepodids to attach to the gills. In natural infection, the flow over the gills is high and reduced flow is required for copepodid settlement. Greatest reductions (96%) in chalimus bath treated with cypermethrin occurred on the gills with no significant reductions in those located on the dorsal and other fins. It is possible that the efficacy of therapeutants may be higher in chalimus attached to the gills because of the higher concentration encountered of bath therapeutant and extrapolation of efficacy to farms may be misleading and progression to field testing is essential.     

花鲈弧菌病病原菌（哈维氏弧菌）的分离与鉴定

1999年4－5月，山东省青岛市胶南海区网箱养殖场花鲈（Lateolabrax japonicus)幼鱼发生暴发性传染病，死亡率达50％。从具有明显症状的病鱼的病灶组织分离到1株优势菌SF－1，经人工感染和从人工感染发病的花鲈再分离的SF－3菌株的再感染试验结果表明，所分离的菌株为此次花钙烂层病的致病菌，经形态、生理生化等64项特征指标鉴定，SF－1和SF－3均为哈维氏弧菌（Vibrio harveyi)。药敏试验结果表明，头孢噻肟，头孢三嗪，头孢孟多，呋喃妥因，氯霉素,氧哌嗪青霉素，磺胺类，复方磺胺、三甲氧苄氨嘧啶，多粘菌素E等10种药物对该菌株有明显的抑制作用。     

Biodegradation potential of aquaculture chemotherapeutants in marine sediments

The commercial chemotherapeutant formulations SLICE^® and AlphaMax^® [active ingredients emamectin benzoate (EB) and deltamethrin respectively] are used in fin fish aquaculture to control parasitic sea lice. In some regions, the use of these substances has drawn concern from the commercial fishing industry regarding potential adverse effects on non‐target organisms. In the present work, biodegradation of EB and deltamethrin, and their commercial formulations, was investigated over 135 days at 4 and 10°C in fresh marine sediments collected from underneath an active open net‐pen salmon farm. EB incubated as either pure substance or commercial formulation was recalcitrant at both temperatures under abiotic and biotic conditions. Deltamethrin incubated alone or as its commercial formulation degraded slowly at 10°C (t_1/2 = 330 ± 107 and 201 ± 27.1 days respectively). At 4°C, deltamethrin degradation was only significant following incubation as commercial formulation (t_1/2 = 285 ±112 days). Degradation rates of EB and deltamethrin as pure substances versus their commercial formulations were not statistically different. Depletion of deltamethrin was observed in 10°C inactive sediments indicating that transformation occurred (at least in part) via an abiotic pathway. Overall, these data provide further insight into the fate and persistence of EB from the ongoing use of SLICE^® in British Columbia's salmon aquaculture industry. AlphaMax^® is not registered in Canada but is used in other salmon farming countries to control sea lice.     

Effects of sea louse chemotherapeutants on early life stages of the spot prawn (Pandalus platyceros)

The effects of five salmon aquaculture anti-sea louse chemotherapeutant active ingredients [azamethiphos (AZ), hydrogen peroxide (HP), emamectin benzoate (EB), cypermethrin (CP) and deltamethrin (DM)] were examined in five life stages (egg, Stage I, Stage III, Stage V and juvenile) of Pacific spot prawn (Pandalus platyceros) for two exposure durations (1-h and 3-h). Endpoints affected by exposures to chemotherapeutants included morbidity in all life stages, egg hatch success, hatchling fitness, latency to moult between successive stages and survival to the juvenile stage. Across life stages, 1-h and 3-h median lethal effect concentrations on morbidity ranged from 73 to 809 mg/L HP; 10–236 µg/L AZ; 321 to >1200 µg/L EB; 0.1 to >5 µg/L CP; and 12 to >1000 ng/L DM. Across endpoints, DM was the most toxic, followed by CP, AZ and EB, followed by HP, which was generally observed to be the least toxic regardless of endpoint examined. The embryo and juvenile life stages were generally more resilient to effects than any larval life stage. Longer duration (3-h) exposures were generally more potent than shorter (1-h) exposures, with up to a threefold greater magnitude of effect when these exposure time frames were compared. Considering predicted environmental concentrations, the estimated greatest risk to ELS spot prawns was observed to be posed by DM, followed by CP, AZ and then EB, with a variable relative risk of HP across different endpoints/life stages.