Differences in susceptibility to Mycobacterium chelonae in zebrafish (Danio rerio) lines commonly used in scientific research.

Mycobacteriosis is one of the most common diseases encountered in laboratory zebrafish. These infections can present a problem to researchers using zebrafish because they may introduce unknown experimental variables. Whilst differences in severity of infections between species of Mycobacterium infecting zebrafish have been well documented, little is known about differences in susceptibility between zebrafish lines. Previous surveys have found higher prevalence in the TU zebrafish line relative to other lines, suggesting that there may be underlying genetic differences in susceptibility. This study investigates Mycobacterium chelonae H1E2-GFP infections in four different zebrafish lines commonly used in research (AB, 5D, casper and TU). Fish were exposed to a labelled (green-fluorescent protein (GFP)) strain of M. chelonae by intraperitoneal injection, and infection status was evaluated after 10 weeks. Visualization of GFP in euthanized fish and histology were used as endpoints. In GFP images, severity was assessed by image analysis, and in histological sections, counts of granulomas containing acid-fast bacteria were used. Results indicated differences in severity of infections between lines, but no significant differences in prevalence.

Histopathology and external examination of heavily parasitized Lost River Sucker Deltistes luxatus (Cope 1879) and Shortnose Sucker Chasmistes brevirostris (Cope 1879) from Upper Klamath Lake, Oregon.

Shortnose Sucker (Chasimistes brevirostris) and Lost River Sucker (Deltistes luxatus) are endemic to the Upper Klamath Basin of Southern Oregon and Northern California, and their populations are in decline. We used histopathology and external examination of 140 and external examination only of 310 underyearling suckers collected in 2013, 2015 and 2016 to document pathological changes, particularly those relating to parasites. The most severe infection was caused by a Contracaecum sp., infecting the atrium of 8%-33% of Shortnose Suckers. The most prevalent infections were caused by Bolbophorus sp. metacercariae in the muscle of Shortnose Suckers (21%-63%) and Lernaea cyprinacea in the skin and muscle of Lost River Suckers (30%-81%). Histology detected Bolbophorus in only 5% of cases where it was not seen externally. Three myxozoans were observed; a Parvicapsula sp. in the renal tubules (10%), a Myxobolus sp. in the intestinal mucosa (2%) and an unusual multicellular, presporogonic myxozoan in the intestinal lumen of one sucker. Severe gill epithelial hyperplasia was observed in several fish collected in 2016. Trichodinids and Ichthyobodo sp. were observed on some of the gills, but absent in many of the fish with severe lesions. A histiocytic sarcoma was observed in sucker.

Hematology and condition factor of tui chub and fathead minnow parasitized by nematode from Upper Klamath Lake, Oregon, USA.

This study evaluated the hematological profile and condition factor (Kn) of tui chub Siphateles bicolor and fathead minnow Pimephales promelas and their associations with larvae of Contracaecum sp. infection of the heart. A total of 30 tui chub and 17 fathead minnow were collected from Upper Klamath Lake, Oregon, USA, measured, and weighed and blood was drawn for hematological analysis. Nematode larvae parasitized tui chub with a prevalence of 50% and mean intensity of 1.40, while 11.8% of fathead minnow were parasitized at a mean intensity of 1.0. Non-parasitized tui chub were significantly larger than the parasitized fish, indicating that small fish could be easily predated by the definitive host, a piscivorous bird. Although the relatively large worm occupied a large portion of the atrium, the presence of the larvae did not affect tui chub Kn, possibly associated with low parasite intensity and a harmonic co-evolution. Only parasitized fathead minnow showed significant differences in red blood cell measurements (greater cell width and larger nuclei) compared to non-parasitized fish. Lymphocytes were the most common white blood cells found in tui chub, followed by neutrophils, monocytes, and periodic acid-Schiff positive granular leukocytes; in fathead minnow lymphocytes were followed by heterophils, monocytes, neutrophils and eosinophils. This study is the first report of Kn and description of blood cells and hematological parameters in these fish species.