Papers by Randolph Richards
Diseases in Asian aquaculture IV: Proceedings of the Fourth Symposium on Diseases in Asian Aquaculture, 22-26 November 1999, Cebu City, Philippines, 2002
Journal of Medical Microbiology, 2018
Mycobacteria are common causative agents of bacterial infections in many species of freshwater an... more Mycobacteria are common causative agents of bacterial infections in many species of freshwater and marine fish. Identification of mycobacteria to the species level based on phenotypic tests is inappropriate and time consuming. Molecular methods such as partial or entire gene sequence determination in mycobacteria have been employed to resolve these problems. The objective of this study was to assess the use of sequence analysis of the mycobacterial 16S-23S internal transcribed spacer (ITS) region for the identification of different aquatic mycobacteria species. Using published primers, ITS sequences of 64 field and reference strains were determined. The identity of all isolates previously identified as M. marinum by restriction fragment length polymorphism (RFLP) DNA profiling was confirmed as M. marinum by sequence analysis. With the exception of five rapidly growing mycobacteria isolates, all other mycobacteria were easily identified by sequencing of the ITS region. Using this spacer region, it was possible to differentiate between slowly growing and rapidly growing mycobacteria, even before sequence analysis, by the size of the PCR product, although species identification could not be made by size alone. Overall, direct sequencing of this genetic element following PCR has been shown to be useful in the identification of aquatic mycobacteria species.
Journal of Fish Diseases, 1994
Piscirickettsia salmonis is a major pathogen of farmed salmonids in Chile and infection with this... more Piscirickettsia salmonis is a major pathogen of farmed salmonids in Chile and infection with this organism can result in significant mortalities (Fryer, Lannan, Giovannoni & Wood 1992). Fanned salmonids exhibiting clinical pathology, histopathology and rickettsia-like organisms (RLOs) resembling that seen in Chile have also been observed in Canada (Brocklebank, Speare, Armstrong & Evelyn 1992) and Ireland (Rodger & Drinan 1993). The recommended methods for presumptive detection of P. salmonis include cell culture or detection in acridine orange (Lannan & Fryer 1991). After detection by these methods, confirmatory identification of the organism can be achieved using an indirect fluorescent antibody test (IFAT) (Lannan, Ewing & Fryer 1991). An alternative rapid confirmation using immunohistochemistry has been demonstrated and is described in this communication. Formalin fixed tissues obtained from farmed Atlantic salmon, Salmo salar L., in Ireland affected by RLOs were embedded in paraffin wax and specimens cut at 5jt/m for immunohistochemistry. Wax-embedded tissue samples of Atlantic salmon, which were experimentally infeeted with P. salmonis in Chile, were obtained from the Veterinary Sciences Faculty,
Journal of Fish Diseases, 2002
The efficacy of emamectin benzoate as an oral treatment of sea lice, Lepeophtheirus salmonis (KrÒ... more The efficacy of emamectin benzoate as an oral treatment of sea lice, Lepeophtheirus salmonis (KrÒyer), infestations in Atlantic salmon, Salmo salar L., was evaluated in a dose titration study and two dose confirmation studies. Replicated groups of salmon with induced infestations of sea lice were given emamectin benzoate on pelleted feed at doses of 0, 25, 50 and 100 μg kg−1 biomass day−1 for seven consecutive days. Sea lice were counted at 7, 14 and 21 days from the start of treatment, and comparisons made with control fish given the same diet without emamectin benzoate. Total numbers of sea lice were significantly reduced at all doses in all three studies when compared to control fish. There was no significant difference between doses of 50 and 100 μg kg−1, but the 50 μg kg−1 dose resulted in significantly fewer lice than the 25 μg kg−1 dose. Emamectin benzoate was highly effective in reducing numbers of preadult and adult lice and prevented the maturation of chalimus to motile st...
Journal of Fish Diseases, 1992
Journal of Fish Diseases, 1991
The minimum inhibitory concentrations (MlCs) of 29 antimicrobial agents were determined for some ... more The minimum inhibitory concentrations (MlCs) of 29 antimicrobial agents were determined for some representative Aeromonas salmonicida. Yersinia ruckeri and Vibrio isolates. Eleven of them, ineluding three widely used in elinieal praetiee, were further tested against 28-36 recent field isolates ot" A. salmonicida. The fluoroquinolones were inhibitor^' at very low concentrations with 50% of A. salmonicida isolates having a MIC of enrofloxaein ^002,t/g ml"'. The distribution of MICs to the fluoroquinolones and to oxohnie acid were similar indicating possible cross resistance. Amoxycillin, florfenicol, minocyeline, rifampicin and the potentiated sulphonamides had a single peak MIC distribution with values of ^1 25^g ml~'. Minimum inhibitory concentrations of the fluoroquinolones were four or more times greater at lO^C compared with 22X; this v/as not so with amoxyeilhn, fiorfenicol or the sulphachlorpyridazine-trimethoprim (S-TP) combination. A. salmonicida was rapidly killed at 22°C by the fluoroquinolones and S-TP whereas oxolinic acid and amoxycillin killed within 24 h. Florfenicol was bacteriostatic. The therapeutic potential of some of these antibiotics is eonsidered.
Journal of Fish Diseases, 1986
Journal of Fish Diseases, 1993
This review surveys the available literature on the effieaey and eeotoxieology of chemotherapeuti... more This review surveys the available literature on the effieaey and eeotoxieology of chemotherapeutic agents for the control of sea lice (Copepoda: Caligidae) infestations in marine aquaculture. To date, treatment for the disease has relied almost exclusively on the use of the organophosphorus pesticides, trichlorfon and dichlorvos. While use of dichlorvos and trichlorfon appears to have little, if any, environmental impact, protracted use in some areas has led to reduced efficacy. Compounds proposed for sea lice control currently under field evaluation include azamethiphos (organophosphate), ivermectin (avermectin), pyrethrum (pyrethrin) and hydrogen peroxide. Although all of these eompounds are effi cacious, at present published information on marine environmental toxicology is scarce and is limited to in vitro toxieity testing. Other compounds that have been considered for sea lice control include formalin, malathion (organophosphate), earbaryl (earbamate), diflubenzuron (insect growth regulator) and natural remedies (i.e. onions and garlic). In general, formaldehyde (aldehyde), malathion and natural compounds show either poor efficacy or unsuitable therapeutic margins. Although earbaryl and diflubenzuron are both efficacious and exhibit suitable therapeutic margins, available data suggests that the compounds, due to undesirable environmental toxieologieal characteristics, would be unsuitable for sea lice control. tf I. Geographic ;iiul laxonomic dislribution of parasitic copcpods and branchiurians recorded in marine fish larming (with iclcrcncc to the genera Argulus, Caligus, Ergasilus, Lepeophtheirus and Pseudocaligus
Journal of Fish Diseases, 1984
A detailed review of proliferative kidney disease (PKD) in salmonids is presented. The introducti... more A detailed review of proliferative kidney disease (PKD) in salmonids is presented. The introduction places the disease in a historical context. The various aspects of the disease are described from the existing literature, together with latest findings from current research. Particular emphasis is given to epidemiology, aetiology and pathology.
Journal of Fish Diseases, 1978
The histological features of the disease caused by infection of turhot by Herpesvirus scophthalmi... more The histological features of the disease caused by infection of turhot by Herpesvirus scophthalmi are described. Infection of epidermal cells of skin and gill resulted in the formation of giant cells showing a variety of nuclear and cytoplasmic changes associated with the replication of the virus. The effects of the condition together with possible control measures are discussed.
Journal of Fish Diseases, 1978
Fungal infection of sexually mature brown trout and char was associated with a particular type of... more Fungal infection of sexually mature brown trout and char was associated with a particular type of Saprolegnia exhibiting a low degree of homothallic sexuality. Hatchery-reared brown trout were more severely infected (in terms of the % area of the body covered with the fungus) than were wild fish. The fins of hatcheryreared fish were particularly prone to Saprolegnia infection regardless of sex. In wild brown trout, a sexual difference in the pattern of infection was demonstrated. The flanks of the male fish appeared to be more prone to infection when compared with the female and there was a greater susceptibility of the caudal and ventral fin of the female when compared with the male. Evidence is presented which suggests that the incidence of infection in mature male salmonid fish prior to spawning is significantly greater than in the females. This difference may not be apparent in spent fish after spawning. These findings are discussed in relation to the background concentration of fungal spores in the water, the behavioural characteristics of spawning fish and differences in epidermal structure.
Journal of Fish Diseases, 1996
The gross, histological and scanning electron microscopic appearance of dorsal fin rot in farmed ... more The gross, histological and scanning electron microscopic appearance of dorsal fin rot in farmed Atlantic salmon parr, Salmo salar L. is described. The lesions were grouped into seven categories: (1) peripheral erosion and ray splitting; (2) peripheral erosion with some nodularity; (3) severe nodularity with differing degrees of tissue loss; (4) extensive to total loss of the dorsal fin; (5) smooth thickening of the dorsal fin; (6) haemorrhagic dorsal fin lesions; and (7) healed dorsal fin rot lesions. The main sign of injury was clefts extending through the epithelium. These injuries were consistent with bites from other parr. During healing from such wounds, damaged cells sloughed from the surface, and there was swelling and hyperplasia in the remaining cells. The majority of the thickening in the fins was the result of epithelial hyperplasia with a variable cellular inflammatory response. The distal epithelium of fins with severe fin rot (i.e. nodular and eroded) was rough, irreg...
Journal of Fish Biology, 1988
The presence of immunoglobulin-containing cells in the epidermis of rainbow trout was traced, usi... more The presence of immunoglobulin-containing cells in the epidermis of rainbow trout was traced, using post-embedding immunocytochemical techniques, in resin-embedded fragments of skin. Light microscopy observations (for which the PAP method was used)revealed the presence of immunoglobulin-containing cells in the epidermis. although no accurate identification was possible. Electron microscopy observations (employing gold-labelling) showed that, in spite of the poor preservation thought unavoidable to protect the antigenicity of the immunoglobulins, the positive cells were either lymphocyte-like cells or mucous cells. Anti-Vibrio anguillarium antibody was detected in the epidermal mucous cells of rainbow trout juveniles vaccinated by immersion, using an immunoenzymatic sandwich technique, modified for resin-embedded tissue. The possibility of the existence of a local immune system is discussed, considering the involvement of the mucous cells.
Journal of Fish Biology, 1983
The kidneys of similar sized rainbow trout from freshwater and seawater environments were examine... more The kidneys of similar sized rainbow trout from freshwater and seawater environments were examined and several parameters of renal corpuscular morphology were measured, The glomeruli of the seawater trout were significantly smaller and contained significantly fewer red blood cells than those of the freshwater fish. There was also some evidence of a decreased number of renal corpuscles per unit area, and an increased proportion with no apparent capsular space in the seawater trout.
Journal of Aquatic Animal Health, 1997
Abstract Tissues from rainbow trout Oncorhynchus mykiss that had been exposed to proliferative ki... more Abstract Tissues from rainbow trout Oncorhynchus mykiss that had been exposed to proliferative kidney disease (PKD) infective waters were sampled from May through to August. These tissues were examined via immunohistochemistry with four monoclonal antibodies (MAbs) previously raised to the causative agent of PKD, a myxosporean termed PKX. The results showed the MAbs were specific for different phases in the parasite's life cycle. Immunogold electron microscopy revealed that three of the MAbs appeared to be specific for vacuoles within the extrasporogonic parasites, and the fourth MAb was specific for secondary cells within the extrasporogonic parasite and for sporogonic stages. Intensification of the staining properties of the parasite through its maturation in the kidney, as demonstrated by immunohistochemistry, indicates that the extrasporogonic parasite may undergo autophagy during the release of maturing secondary cells.
Journal of Aquatic Animal Health, 1996
ABSTRACT
Fish & Shellfish Immunology, 2013
Species within the genus Francisella are highly pathogenic in mammals. Recently an emerging fish ... more Species within the genus Francisella are highly pathogenic in mammals. Recently an emerging fish pathogen and novel species of Francisella has caused significant mortalities in farmed fish including tilapia and Atlantic cod. To learn more about virulence mechanisms utilized by this pathogen,
Aquaculture, 2000
levels of infectivity were still detectable after 30 min exposure to 100 ppm of either disinfecta... more levels of infectivity were still detectable after 30 min exposure to 100 ppm of either disinfectant. Treatment with an acid peroxygen disinfectant rapidly reduced virus infectivity in both distilled water and serum supplemented diluent within 5 min but infectious virus was not totally eliminated even after exposure for 30 min.
Aquaculture, 2000
Three field trials were conducted to evaluate the efficacy of emamectin benzoate as a treatment Ž... more Three field trials were conducted to evaluate the efficacy of emamectin benzoate as a treatment Ž. Ž. for sea lice, Lepeophtheirus salmonis Krøyer and Caligus elongatus Nordmann , infestations on Ž. Atlantic salmon Salmo salar L.. Trials were carried out at sea temperatures of 13.0-15.58C and 7.2-8.58C. Salmon naturally infested with sea lice, with mean weights of 438, 513 and 2662 g, respectively, were held in experimental pens on commercial sites. At day y1 or y2, 20 or 30 fish were sampled from each pen to determine pre-treatment numbers of lice. Emamectin benzoate was administered in-feed at a dose of 50 mg kg y1 biomass day y1 for 7 consecutive days. Sea lice were counted again on days 7, 14 and 21, and comparisons made with untreated control fish. Treatment with emamectin benzoate was effective against chalimus and motile stages of sea lice. In all three trials, treated groups were surrounded by pens of heavily infested fish and L. salmonis numbers increased over time on control fish by 87-284%, whereas over the same period, L. salmonis were reduced on treated fish by 68-98%. In the low temperature trial, reductions were slower but numbers were still 90% lower than on control fish at day 21. At the end of the
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Papers by Randolph Richards