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Severe outbreaks of black gill (BG), heavily melanized gills of crustaceans, have been reported in white ( Litopenaeus setiferus) and brown shrimp ( Farfantepenaeus aztecus) from coastal Georgia and South Carolina during late summer and fall since the mid-1990s. The cause of this condition is an apostome ciliate that elicits the innate immune response of the shrimp, resulting in the formation of melanized nodules in shrimp gill tissue. In the absence of a definitive identification, the causative ciliate is referred to as the shrimp black gill (sBG) ciliate. During outbreaks, necrosis of gill tissue was often seen in microscopic sections; in some cases, there appeared to be penetration of the ciliate into gill tissue. Shrimp with BG exhibited reduced physical endurance and escape responses compared with shrimp without symptomatic BG. Physical impairment due to BG may contribute to higher predation rates and increased vulnerability to environmental conditions. The infection transmission rate of the sBG ciliate appears to be atypically low for apostome ciliates, raising the question of how epidemic levels of BG reoccur annually. Asymptomatic shrimp placed in direct contact with carcasses (heads) from BG symptomatic shrimp exhibited a significant increase in the development of BG symptoms after 7 days ( P = 0.028), but waterborne transmission was not detected. A preliminary survey of sympatric crustacean species, including syntopic species of grass shrimp ( Palaemonetes spp.), indicated the possible presence of the sBG ciliate, suggesting that other crustacean species may serve as infection reservoirs. These studies support the conclusion that BG is negatively impacting the penaeid shrimp fishery and highlight the challenges that remain in understanding and managing the ongoing sBG epidemic in the southeastern United States. [ABSTRACT FROM AUTHOR]

Penaeid shrimp including Litopenaeus setiferus (white shrimp), Farfantepenaeus aztecus (brown shrimp), and Farfantepenaeus duorarum (pink shrimp) support one of the most valuable commercial fisheries in the U.S. Southeast Atlantic. Since the late 1990s, the fishery, especially in coastal Georgia and South Carolina, has experienced a significant decline. A contributing factor to this decline has been hypothesized to be a severe outbreak of shrimp black gill caused by a ciliate parasite. DNAsequence-based analysis of the gill parasite small subunit rRNA gene identifies the proposed causative agent as being closely related to the apostome ciliate Hyalophysa chattoni; however, morphological characteristics of the ciliate observed by electron microscopy are inconsistent with this identification. Although studies are ongoing to identify this ciliate, it was possible to develop a diagnostic polymerase chain reaction-based assay targeting the small subunit rRNA gene and use it to investigate the seasonal and geographic distribution of the parasite in wild shrimp populations. Next-generation sequencing of the gill microbiome confirmed that when black gill is at its peak, microeukaryotic communities were dominated by apostome-related ciliates, but over the year highly diverse communities of gill associates, including other potential ciliate, fungal, euglenozoid, and amoeboid parasites are commonly detected. Improved molecular diagnostics and the ability to explore the diversity of potential parasites in shrimp provide important new insights into the relationship between the shrimp fishery and black gill. [ABSTRACT FROM AUTHOR]

The tropically associated black mangrove ( Avicennia germinans) is experiencing a climate-induced range shift and expanding into salt marshes of northern Florida, southern Louisiana and most recently, Horn Island, MS. To date, little is known about how black mangroves function as nursery habitat for important fishery species such as shrimps or how their increase may affect survival of such species. The main objective of our study was to determine habitat preference and survival rates of common, economically important penaeid shrimps in the presence and absence of the increasingly abundant tropical predator, the gray snapper ( Lutjanus griseus). We also examined the effects of habitat identity and structure on juvenile white shrimp ( Litopenaeus setiferus) and brown shrimp ( Farfantepenaeus aztecus) behavior, using preference experiments in indoor mesocosms both with and without the predatory gray snapper. Results showed that shrimp prefer Spartina over Avicennia with or without predation risk. Survival of shrimp was lowest in sand and highest in medium-density Spartina. Thus, a marsh-to-mangrove habitat conversion could ultimately result in decreased shrimp survival. [ABSTRACT FROM AUTHOR]

In penaeid shrimp species, vitellogenin (VTG) synthesis in the ovary and hepatopancreas is under the inhibitory regulation of a neuroendocrine system, the X-organ/sinus gland complex in the paired eyestalks, and eyestalk ablation (removal of the X-organ/sinus gland complex) is widely used for inducing ovarian development. However, the difference in effects of bilateral and unilateral ablation on VTG gene expression has not been clarified so far. In the present study, VTG synthesis was monitored over a 16-day period after ablation and compared between replicates of immature female kuruma prawns, Marsupenaeus (Penaeus) japonicus, that had been bilaterally or unilaterally ablated and control specimens. After bilateral ablation, ovarian development was induced, and the ovarian weight, hemolymph VTG levels, and VTG mRNA levels in the ovary increased significantly. Significant VTG mRNA increase was detected 12 h after bilateral ablation. In contrast, after unilateral ablation, ovarian development was not induced, and the ovarian weight, hemolymph VTG levels, and VTG mRNA levels in the ovary did not change significantly from the control. These results indicate that in immature female prawns, unilateral ablation does not induce VTG gene expression, whereas bilateral ablation induces rapid VTG gene expression (<12 h). The ineffectiveness of unilateral ablation suggests that the remaining X-organ/sinus gland complex in the unilaterally ablated female prawns may secrete sufficient VIH to suppress VTG synthesis. [ABSTRACT FROM AUTHOR]