Denman Island disease (causative agent Mikrocytos mackini) in a new host, Kumamoto oysters Crassostrea sikamea

Abstract

Mikrocytos mackini, causative agent of Denman Island disease in Pacific oystersCrassostrea gigas and other oyster species, was found in 2011 in a previously unreported host, the Kumamoto oyster C. sikamea, in Humboldt Bay, California, USA. The detection was also the first reported finding of M. mackini in California. Prevalence was estimated as high as approximately 27% from pooled samples analyzed by PCR. Higher prevalence appeared related to longer residence time in the bay and somewhat colder than typical winter seawater temperatures. No M. mackini was detected in Humboldt Bay juvenile Kumamoto oysters or Pacific oyster brood or seed stock in 2011 or 2012. KEY WORDS: Mikrocytos mackini · Denman Island disease · Kumamoto oyster · Crassostrea sikamea Resale or republication not permitted without written consent of the publisherDis Aquat Org 102: [65][66][67][68][69][70][71] 2012 shellfish farms, consisting of independent sampling conducted by US Department of Agriculture accredited veterinarians. As a result of such routine surveillance in 2011, Mikrocytos mackini infections were discovered in a previously unrecognized host species, Kumamoto oysters Crassostrea sikamea in Hum boldt Bay, California, a location previously unknown to harbor the disease agent. MATERIALS AND METHODS Sample collectionKumamoto and Pacific brood and seed stock oysters were initially sampled (n = 600) from the northern arm of Humboldt Bay, in February 2011 as part of annual routine brood stock disease sur veillance (Table 1). Samples are collected by an independent veterinarian accredited by the US Department of Agriculture, Animal and Plant Health In spection Service. Following the detection of Mikrocytos mackini from the February sampled group, additional Kumamoto and Pacific oyster brood and seed stock were sampled from March to May 2011 by producer collections from Humboldt Bay (n = 600, Table 1). Except as noted in Table 1, brood stock was held on long lines and seed stock was held in floating up weller systems (FLUPSY). In addition to results of testing on samples collected in 2011, we also report results from samples collected by an accredited veterinarian for disease surveillance in 2012 (n = 600, see Table 1). Histological testingAll oysters were processed for histological examination using routine methods. A transverse section of oysters was made in the dorsal region through the digestive gland, gills and connective tissue, including the labial palps in some cases. This was placed in a histological cassette and fixed in seawater formalin (10% v/v). Histological preparations were processed routinely for paraffin embedment and sections were stained with hematoxylin and eosin. In addition to the examination of tissue for hemocytosis and infectious agents, the height of the epithelium of the digestive gland tubules was rated on a basis of 1 to 4 (low to high), with ratings of 3 and 4 considered to be in the normal active feeding range and ratings of 1 or 2 indicating low height of digestive gland epithelium resulting ...

Recurrent Water Level Fluctuation Alleviates the Effects of Submergence Stress on the Invasive Riparian Plant Alternanthera philoxeroides

“…Although it is known that submergence (increasing water levels) can inhibit plant growth [4, 12, 15, 27, 32], our study shows that the effects of water level are dependent on fluctuation frequency. Plants that are able to escape levels of submergence that are disadvantageous to their growth can continue to accumulate biomass.…”

“…While rising water levels submerge plants, falling water levels indicate water scarcity, creating water stress for plants. Many experiments have been performed to study the effects of submergence on riparian plants, reporting various morphological and physiological adjustments to submergence [12–18]. Other studies have addressed the response of plants to submergence and de-submergence [9, 19], as well as the effects of the amplitude of water level fluctuation [5, 20–23].…”

Descriptions of Mikrocytos veneroïdes n. sp. and Mikrocytos donaxi n. sp. (Ascetosporea: Mikrocytida: Mikrocytiidae), detected during important mortality events of the wedge clam Donax trunculus Linnaeus (Veneroida: Donacidae), in France between 2008 and 2011

“…This parasite was responsible for Denman Island disease in the wild and cultured Pacific oyster Crassostrea gigas Thunberg, 1793 in British Columbia, Canada, where it induced severe oyster mortalities [ 8 ]. It could naturally affect other oysters, such as the Olympia oyster Ostrea lurida Carpenter, 1864 [ 10 ] or the Kumamoto oyster Crassostrea sikamea Amemiya, 1928 [ 11 ]. Since its detection, the range extension of this parasite has been limited to the west coast of North America, in Canada and the USA [ 9 , 11 – 13 ]; it has never been detected in Europe.…”

“…It could naturally affect other oysters, such as the Olympia oyster Ostrea lurida Carpenter, 1864 [ 10 ] or the Kumamoto oyster Crassostrea sikamea Amemiya, 1928 [ 11 ]. Since its detection, the range extension of this parasite has been limited to the west coast of North America, in Canada and the USA [ 9 , 11 – 13 ]; it has never been detected in Europe. Because of its potential impact on oyster farming, this parasite is regulated in Europe and surveillance is implemented in different European countries in order to prevent its introduction.…”

Infection of Manila clams Ruditapes philippinarum from Galicia (NW Spain) with a Mikrocytos-like parasite

“…Re cently, it has also been detected in Washington State (USA) (Bower 2010, Abbott et al 2011) and has been found to infect C. sikamea from California (USA) (Elston et al 2012). M. mackini is included in the group of microcell parasites of molluscs due to its small size (2−4 µm), together with haplosporidian parasites of the genus Bonamia.…”