Myxobolus spp. (Cnidaria: Myxozoa) in introduced yellow perch Perca flavescens (Mitchill, 1814).

We surveyed introduced yellow perch Perca flavescens (Mitchill, 1814) from the Willamette River, OR, USA, to determine if these fish have co-introduced myxosporean parasites. Mature parasite myxospores were observed in brains of 3/19 fish, and were morphologically and molecularly consistent with Myxobolus neurophilus (Guilford 1963), a parasite known from yellow perch in their native range. We identified another Myxobolus species from the gill filaments of 1/22 fish. The spores from the gill filaments were oval-shaped, 11.7 (10.7-12.3) µm long × 8.6 (7.7-9.0) µm wide × 5.2 (4.6-5.6) µm thick, with two oval-shaped polar capsules 5.7 (5.1-6.5) µm × 2.7 (2.4-3.2) µm, each containing a polar tubule with 8-9 turns. Small-subunit ribosomal DNA sequences from each of four plasmodia were identical, and 4.0% different (over 1800 nucleotides) from the closest known myxosporeans. Interestingly, these sequences had overlapping peaks in their chromatograms, which suggested that DNA from multiple species was present. Hence, we isolated and sequenced three individual myxospores and found that they too had mixed chromatograms, which indicated presence of at least two sequence types of small-subunit ribosomal DNA in each spore (GenBank accession MK592012, MK592013), a rare character among described myxosporeans. The spore morphology, morphometry, tissue tropism, and DNA sequence supported a diagnosis of a novel species, Myxobolus doubleae n. sp. This parasite is unknown from yellow perch in its native range, despite extensive historical surveys, which suggests that introduced yellow perch might have acquired an endemic Myxobolus species via spillback from another fish host.

Comparing the expected refractive status from immersion biometry and the achieved refractive status post-cataract surgery

Objective: To investigate the accuracy of Immersion A-Scan Biometry by comparing the relationship between the predicted refractive status from the biometric data with the achieved refractive status determined from objective/subjective refraction. Design and Methodology: Sixty patients were recruited from the Trinidad Eye Hospital (TEH) who was scheduled to undergo cataract surgery. The method of ocular biometry measurement used in this study was Immersion A-scan Biometry using the Aviso: The Ultrasound Platform. The biometric data was then recorded along with the expected refractive status based on the SRK-T formula used to calculate the power of the intra-occular lens (IOL) to be implanted. Results: Out of the 60 patients used, phacoemulsification surgery was performed on 33 right eyes and 27 left eyes. The goal of emmetropia after surgery was achieved in 32 patients among the 60 patients. The 28 patients that were unable to achieve emmetropia brought awareness to the assumptions of errors within the biometric data. The visual acuity was improved significantly in all patients after the phacoemulsification surgery. Conclusion: The study confirmed that there is no significant difference between the refractive status predicted from Immersion A-scan biometry with the refractive status achieved post cataract surgery.

Experimental vertical transmission of Piscirickettsia salmonis and in vitro study of attachment and mode of entrance into the fish ovum.

Piscirickettsia salmonis is a pathogenic bacterial agent causing septicaemic disease in salmon. Since its isolation in Chile in 1989, P. salmonis has continually produced high mortality rates in salmon farms. Little information exists regarding the mechanisms of vertical transmission of this pathogen. Experimental vertical transmission was established in the present study by inoculation of male and female rainbow trout broodstock with P. salmonis. The bacterium was subsequently detected using indirect immunofluorescence in milt and coelomic fluid of the majority of inoculated broodstock (14/15). Bacteria were detected in the fry when 1 or both parents were inoculated, although none of the infected fry presented signs of the disease. P. salmonis was also detected in progeny obtained through fertilisation ova from non-inoculated females incubated in a medium containing a bacterial suspension, demonstrating transmission during the process of fertilisation. Ova infected in vitro were examined at sample periods from 30 s to 60 min using scanning electron microscopy. This demonstrated that the bacterium attaches to the ova by means of membrane extensions, structures which we have called 'piscirickettsial attachment complex' (PAC) and which would allow later penetration into the ovum.

Relative virulence of three isolates of Piscirickettsia salmonis for coho salmon Oncorhynchus kisutch.

Piscirickettsia salmonis was first recognized as the cause of mortality among pen-reared coho salmon Oncorhynchus kisutch in Chile. Since the initial isolation of this intracellular Gram-negative bacterium in 1989, similar organisms have been described from several areas of the world, but the associated outbreaks were not reported to be as serious as those that occurred in Chile. To determine if this was due to differences in virulence among isolates of P. salmonis, we conducted an experiment comparing isolates from Chile, British Columbia, Canada, and Norway (LF-89, ATL-4-91 and NOR-92, respectively). For each of the isolates, 3 replicates of 30 coho salmon were injected intraperitoneally with each of 3 concentrations of the bacterium. Negative control fish were injected with MEM-10. Mortalities were collected daily for 41 d post-injection. Piscirickettsiosis was observed in fish injected with each of the 3 isolates, and for each isolate, cumulative mortality was directly related to the concentration of bacterial cells administered. The LF-89 isolate was the most virulent, with losses reaching 97% in the 3 replicates injected with 10(5.0) TCID50, 91% in the replicates injected with 10(4.0) TCID50, and 57% in the fish injected with 10(3.0) TCID50. The ATL-4-91 isolate caused losses of 92% in the 3 replicates injected with 10(5.0) TCID50, 76% in the fish injected with 10(4.0) TCID50, and 32% in those injected with 10(3.0) TCID50. The NOR-92 isolate was the least virulent, causing 41% mortality in the replicates injected with 10(4.6) TCID50. At 41 d post-injection, 6% of the fish injected with 10(3.6) TCID50 NOR-92 had died. Mortality was only 2% in the fish injected with 10(2.6) TCID50 NOR-92, which was the same as the negative control group. Because the group injected with the highest concentration (10(4.6) TCID50) of NOR-92 was still experiencing mortality at 41 d, it was held for an additional 46 d. At 87 d post-injection, the cumulative mortality in this group had reached 70%. These differences in virulence among the isolates were statistically significant (p < 0.0001), and are important for the management of affected stocks of fish.