Reo-Like Virus in White Shrimp Penaeus vannamei (Crustacea: Decapoda): Co-occurrence with Baculovirus penaei in Experimental Infections

A virus, tentatively identified as reo-like, occurred concurrently with experimentally-induced Baculovirus penaei (BP) infection in cultured white shrimp larvae Penaeus vannamei. Each shrimp with a reo-like viral infection also had a BP infection, but not all BP-infected shrimp had a reo-like infection. Both viruses occurred in the same tissues and occasionally withln the same cell. The reolike virus developed in epithelial cells of the anterior midgut and in reserve- and fibrillar-cells of the hepatopancreas. The paraspherical and non-enveloped reo-like virions (ca. 50 nm diam.) occurred as unordered aggregates in the cell cytoplasm. Their etiology has not been determined. Reo-like virions may have been introduced along with the BP virus, or, were latent and only manifested due to stress induced by the more pathogenic BP virus.

Paraophioidina scolecoides n. sp., a New Aseptate Gregarine from Cultured Pacific White Shrimp Penaeus vannamei

The aseptate gregarine Paraophloidina scolecoides n. sp. (Eugregarinorida: Lecudinidae) heavily infected the midgut of cultured larval and postlarval specimens of Penaeus vannamei from a commercial 'seed-production' facility in Texas, USA. It is morphologically similar to P. korotneffi and P. vibiliae, but it can be distinguished from them and from other members of the genus by having gamonts associated exclusively by lateral syzygy. Shrimp acquired the infection at the facility; nauplii did not show any evidence of infection, but protozoea, mysis, and postlarval shrimp had a prevalence and intensity of infection ranging from 56 to 80 % and 10 to >50 parasites, respectively. Infected shrimp removed from the facility to aquaria at another location lost their gamont infection within 7 days When voided from the gut, the gregarine disintegrated in seawater. Results suggest that P. vannamei is an accidental host, although a survey of representative members of the invertebrate fauna from the environment associated with the facility failed to discover other hosts. No link was established between infection and either the broodstock or the water or detritus from the nursery or broodstock tanks.

Relationship Between BP (Baculovirus penaei) Energy Reserves in Larval and Postlarval Pacific White Shrimp Penaeus vannamei

The relationship between energy reserves of the penaeid shrimp Penaeus vannamei and Baculovirus penaei, or BP, were investigated in a series of experiments using mysis stage or early postlarval shrimp. Pre-exposure and post-exposure levels of protein and triacylgycerol (TAG) were determined. The effect of pre-exposure protein and TAG levels on susceptibility to BP infections was also investigated by starving a group of shrimp immediately prior to BP exposure. There was no consistent relationship between either pre-exposure or post-exposure protein levels and the percent of shrimp developing patent BP infections. There was, however, a significant positive correlation between TAG levels immediately prior to viral exposure and prevalence of infection 72 h later. Experimental reduction of TAG reserves prior to BP exposure delayed the development of a patent infection. In some, but not all, experiments there was a significant reduction in TAG levels of infected compared with uninfected shrimp 72 h post-exposure. The effect of patent BP infections on host TAG levels was subordinate to fluctuations in TAG content associated with the ontogeny of the hepatopancreas. Results of this study support histological observations that shrimp lipid levels can be altered by baculovirus infections. Furthermore, high levels of energy reserves in the form of TAG are associated with increased susceptibility to BP infection in larval and postlarval shrimp.

Diatoms in the Gills of the Commercial White Shrimp

A white shrimp from Galveston, Texas, is the first reported case of a crustacean internally infected by a diatom. Even though more than one species occurred in debris on and between gill filaments, only individuals of Amphora sp. occurred within gills. To determine if a related diatom would easily reproduce within the shrimp and cause. a host response similar to that observed, we injected cultured specimens of A. coffaeformis into white shrimp. Under the experimental conditions, individuals of that species did not divide, but they elicited an extensive melanistic host-response.

A Filamentous Bacterium on the Brine Shrimp and Its Control

A strain of a colorless, filamentous bacterium (tentatively identified as Leucothrix mucor) heavily infests the brine shrimp, Artemia salina. Its ultrastructure, unlike that of some other strains, does not reveal a distinct middle layer between its outer cell wall layer and cytoplasmic membrane, irregular blebs extending from the cell layers, or an external sheath. An entire infestation, represented as a mat of the bacterium with associated debris and microorganisms, sloughs from the shrimp when exposed to a variety of treatments. Primarily because most effective treatments are toxic to the shrimp, 100 ppm terramycin provides the treatment of choice.

Radiocarbon Dating, Chronologic Framework, and Changes in Accumulation Rates of Holocene Estuarine Sediments from Chesapeake Bay

Rapidly accumulating Holocene sediments in estuaries commonly are difficult to sample and date. In Chesapeake Bay, we obtained sediment cores as much as 20min length and used numerous radiocarbon ages measured by accelerator mass spectrometry methods to provide the first detailed chronologies of Holocene sediment accumulation in the bay. Carbon in these sediments is a complex mixture of materials from a variety of sources. Analyses of different components of the sediments show that total organic carbon ages are largely unreliable, because much of the carbon (including coal) has been transported to the bay from upstream sources and is older than sediments in which it was deposited. Mollusk shells (clams, oysters) and foraminifera appear to give reliable results, although reworking and burrowing are potential problems. Analyses of museum specimens collected alive before atmospheric nuclear testing suggest that the standard reservoir correction for marine samples is appropriate for middle to lower Chesapeake Bay. The biogenic carbonate radiocarbon ages are compatible with 210Pb and 137Cs data and pollen stratigraphy from the same sites. Post-settlement changes in sediment transport and accumulation is an important environmental issue in many estuaries, including the Chesapeake. Our data show that large variations in sediment mass accumulation rates occur among sites. At shallow water sites, local factors seem to control changes in accumulation rates with time. Our two relatively deep-water sites in the axial channel of the bay have different long-term average accumulation rates, but the history of sediment accumulation at these sites appears to reflect overall conditions in the bay. Mass accumulation rates at the two deep-water sites rapidly increased by about fourfold coincident with widespread land clearance for agriculture in the Chesapeake watershed.