Cause Of Mass Mortality Research Articles

Natural Bacterial Co-Infection in Farmed European Sea Bass Intended for Experimental Research in Sicily, Southern Italy: Pathological Findings

In mariculture facilities, bacterial infections pose significant production challenges, with potentially catastrophic impacts on fish species. Bacterial co-infections are a widespread phenomenon in the natural marine environment, although their impact on aquatic organisms remains poorly investigated. This study aimed to detail the pathological findings associated with a natural bacterial co-infection caused by three different pathogens, namely Photobacterium damselae subsp. piscicida, Tenacibaculum maritimum and Vibrio sp., as the cause of mass mortality in European sea bass. The fish had been reared in open-net cages in Sicily and later transferred for experimental research purposes to a user establishment after immunization with an inactivated vaccine. Macroscopic, cytological and histopathological examinations were performed on 109 animals, and bacterial species were identified by the 16S rRNA gene. Overall, ulcerative skin lesions, necrotizing myositis and tail rot with occasional tail loss were associated with tenacibaculosis and vibriosis, while P. damselae subsp. piscicida mainly caused granulomatous inflammation in the spleen and head kidney. Finally, an injection site reaction due to the oil-adjuvanted vaccine administered intraperitoneally was observed in the abdominal fat. Understanding the impact of bacterial pathogens is essential to manage the health and welfare of farmed fish, and the importance of a good health monitoring program cannot be overstated to avoid outbreaks and the possible emergence of new pathogens due to the intensification of the production systems, antibiotic resistance and climate changes. The study would also highlight the importance of the quarantine period when animals supplied for research come from aquaculture farms and how the main goal in the near future should be to better define the procedures to provide completely pathogen-free animals.

Volcanism-driven lacustrine redox fluctuations were responsible for the formation of the Jehol Lagerstätte: Evidence from a high-resolution Aptian sedimentary core, Northeast China

While a “volcanic Pompeii” model is well accepted as the cause of mass mortality and exceptional preservation of the Jehol Biota, no consensus has been reached thus far regarding the cause of mass mortality of fossils found in interbedded finely laminated sediments. We propose that volcanically driven, lacustrine redox fluctuations were responsible for the formation of the Jehol Lagerstätte, based on data obtained from a new drill core of Lower Cretaceous sedimentary rocks in the Chaoyang Basin, Northeast China. We found manganese-rich carbonates are interbedded with molybdenum-rich black mudstones and tuffs, and phosphatized fossils in the drill core. The elemental enrichment factors for molybdenum are much higher than for uranium in the black mudstones, suggesting the role of the manganese particulate-shuttle in deposition of this element. The manganese-rich carbonates are formed by the reaction of manganese oxides with organic matter, indicating an oxidized water column. This process accelerates the enrichment of molybdenum under anoxic non-sulfidic conditions. The interbedded manganese carbonates and molybdenum-rich mudstones thus record redox fluctuations in the lacustrine depositional environment. Given the numerous tephra in the black mudstones and soft-sediment deformation structures ostensibly associated with seismicity, we propose that the redox fluctuations were caused by lake eutrophication and turnover driven by volcanism that was ultimately related to the destruction of the North China Craton. These volcanically induced redox fluctuations, along with the toxicity of the volcanic gases, may have caused the simultaneous mass mortality of aquatic, terrestrial, and avian fauna. Micro-X-ray fluorescence, energy dispersive X-ray spectroscopy, and Raman mapping show that the preservation of fossils was mainly due to phosphatization. Fluctuating redox conditions facilitated phosphate enrichment in sediments. Both the oxic and anoxic non-sulfidic conditions were conducive to the preservation of organisms by phosphatization, and oxidation was favorable for phosphate mineralization, both contributing to the exceptional preservation of the Jehol Biota fossils.

Eucera bees (Hymenoptera, Apidae, Eucerini) preserved in their brood cells from late Holocene (middle Neoglacial) palaeosols of southwest Portugal

AbstractThe c. 100 myr extensive fossil record of bee brood nests and cells (calichnia) in siliciclastic sedimentary deposits, or palaeosols, is virtually devoid of the presence of their producers. The absence of a more specific assignment to a producer of the different ichnogenera of the ichnofamily Celliformidae precludes their use in phylogenetic and palaeobiogeographic studies. Omission surfaces developed in incipient carbonate palaeosols during the late Holocene (middle Neoglacial), c. 2975 yr cal BP, on the southwest coast of mainland Portugal show insect calichnia in dense ichnofabrics dominated by shallow discrete cells (Palmiraichnus castellanosi) and cells at the terminus of vertical shafts. At Carreira Brava, one of the studied sites, bees ready to abandon their cells were found in an exceptional state of preservation inside the sealed brood chambers. The chambers also preserve the inner cell hydrophobic polymerized membrane and remains of the monospecific Brassicaceae‐type pollen provision. Although the cause of mass mortality remains a mystery, oxygen depletion due to sudden flooding of the nesting substrate and consequent or overnight temperature drop, just before emergence, are plausible causes. The anaerobic conditions and later rapid carbonate diagenetic lithification are the likely causes of the preservation of the bees and the inner cell organic membrane. The favourable climate conditions for the development of successive, dense ichnofabrics from an omission suite dominated by bee brood cells may be the result of slightly colder and higher‐precipitation winters during the Neoglacial interval.

Dietary analysis of three important mariculture species in South Korea using DNA metabarcoding in fecal samples

Knowledge of dietary composition is crucial for understanding the trophic ecology of a mariculture species and the available food in aquafarms, which is fundamental for assessing ecosystem health status and determining ecological response to ecosystem variation to develop a better management plan for marine farming. For suspension-feeding invertebrates, the growth and development rely heavily on the availability and quality of phytoplankton. However, their growth rate can be severely impacted by food deficiency or exposure to harmful algae blooms (HABs) and pathogenic parasites, which are major causes of mass mortality in mariculture. This study aimed to conduct a dietary analysis of three important mariculture species — Magallana gigas, Halocynthia roretzi, and Mizuhopecten yessoensis — on three farms in South Korea using DNA metabarcoding. Sequence processing and filtering generated 304 validated amplicon sequence variants from six fecal samples, taxonomically identifying 15 phyla, 18 classes, 32 orders, 39 families, 43 genera, and 46 species. The DNA recovery of Dinoflagellata was predominantly detected in all fecal samples, followed by Apicomplexa, Bacillariophyta, and Ciliophora. Of the three mariculture species, the fecal assemblage of M. gigas exhibited the highest richness and diversity, with a high read proportion of phytoplankton (specifically Dinoflagellata), while such proportions were relatively low in the M. yessoensis samples. Excessive read proportions of parasites (Apicomplexa) were detected in the fecal samples of two H. roretzi, indicating a possible link to as substantial decrease in H. roretzi production observed in South Korea. A total of 27 key species were detected in six fecal samples, including a high read proportion of Prorocentrum triestinum, which is responsible for HABs in Korean coastal waters. These results emphasize the potential of fecal DNA metabarcoding in the genetic monitoring of aquaculture farms/ecosystems and could be a useful reference for develop effective management plans to guarantee sustainable mariculture production.

Complete Genome Sequences of Two Pasteurella multocida Isolates from Seabirds.

Pasteurella multocida is one of the major causes of mass mortalities in wild birds. Here, we report the complete genome sequences of two P. multocida isolates from wild populations of two endangered seabird species, the Indian yellow-nosed albatrosses (Thalassarche carteri) and the northern rockhopper penguins (Eudyptes moseleyi).

Transcriptome analysis of high mortality phenomena in polyploid fish embryos: An allotriploid embryo case study in hybrid grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂)

Triploidization of diploid fish is an ideal means for achieving polyploid breeding. During the preparation of allotriploid grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂), the allotriploid embryos (T) had a much higher morality from the high blastula to middle gastrula stage compared to the normal hybrid diploids (D). Therefore, the internal regulation of gene expression in allotriploid fertilized grouper eggs was explored by comparing the transcriptional profiles of T and D mapped at the high blastula (1), middle gastrula (2), and crystal (3) stages using the Illumina RNA-seq technology. There were 2357 differentially expressed genes (DEGs) found only in T1_vs_T2 and 1585 DEGs found only in T2_vs_T3. According to the GO functional enrichment analysis, when T developed from the high blastula to middle gastrula stage (i.e., pre-embryonic development; T1_vs_T2), the DEGs showed significant enrichment in terms associated with the cell cycle and cytoskeleton, indicating that cell proliferation was inhibited. KEGG pathway analysis of DEGs showed significant enrichment in mRNA processing and translation and in pathways associated with programmed cell death (PCD). Cell differentiation can trigger PCD and the combined effects of up-regulated ripk1, dnm1l, pgam5, Slc25a5, and vdac1 expression and down-regulated fadd expression during pre-embryonic development may have been the main cause of mass mortality in embryos up until the middle gastrula stage. A two-by-two comparison of D2_vs_T2 DEGs at the middle gastrula stage to the aforementioned DEGs expressed only in T revealed that the Parp4 and pole were down-regulated in the pre-development of T, which might lead to decreased DNA repair efficiency. These results could have reflected either (1) the altered physiological state of the cells due to cold-shock treatment or (2) the sensitivity of pre-embryonic development to an elevated number of chromosomes, which induced disrupted gene expression and abnormal cell division. In conclusion, the above study helps explain why allotriploid grouper exhibit high mortality at the middle gastrula stage, improves our understanding of the regulation of triploid embryo development, and provides basic information for reducing mortality at the middle gastrula stage.

Occurrence and Characterization of Enterococcus Faecalis from Infected Farmed African Catfish in Ogun State, Nigeria

Background: The opportunistic fish pathogen are the main cause of mass mortality in several fish species and severe economic losses in different countries. This study was conducted to determine occurrence and characterization of Enterococcus faecalis from infected farmed African catfish in Ogun State, Nigeria. Methodology: The bacteria was isolated from infected farmed African catfish (Clarias gariepinus, n=128) with clinical signs of atrophied or reduced barbels, desquamation or abrasion of the skin, and ascites were purposively sampled in Ogun State. The isolates were identified based on morphological, biochemical tests, and 16S rRNA molecular characterization. The 16S rRNA gene sequence was analyzed using BLAST, submitted to the NCBI database, and an accession number was generated. Results: The percentage occurrence of Enterococcus faecalis isolates in infected Clarias gariepinus from Ogun State were; Ogun East 30.00% (18/60); Ogun Central 17.86% (5/28); Ogun West 12.50% (5/40). The highest incidence (p < 0.05) in Ogun State recorded was in Ijebu Ode local government compared to other local governments area. All Enterococcus faecalis isolates in this study were non-motile, gram-positive cocci, showed negative reaction for catalase, negative for oxidase, negative for methyl-red, and negative for indole. 16S rRNA gene of Enterococcus faecalis isolates in infected Clarias gariepinus from Ogun State, Nigeria (OP595802.1) was closely related to 16S rRNA gene of other Enterococcus faecalis isolates Conclusions: The bacteria isolated from infected farmed Clarias gariepinus in Ogun State, Nigeria was Enterococcus faecalis, and showed an evolutionary relationship with NCBI reference global strains from different countries.

Use of Sonneratia alba leaf extract solution for White Spot Syndrome Virus prevention in tiger shrimp postlarvae

White Spot Syndrome Virus (WSSV) is one of the leading causes of mass mortality in tiger shrimp culture. The objective of this study was to determine the impact of different immersion times in 1% Sonneratia alba extract on the ability of WSSV infected tiger shrimp to survive as post-larvae. Eight treatments were used in this study, with three replications for each. The treatments were as follows: A) 12 hours of immersion; B) 24; C) 36; D) 48; E) 60; F) 72; G) Positive control (infected with WSSV but without mangrove extract); and H) Negative control (without WSSV infection and mangrove extract). with three replications in each treatment. Tiger prawn post-larvae were stocked at a density of 20 squares per jar. At a rate of 20% of the daily biomass, they were being fed three times per day. Tiger shrimp post-larvae mortality was examined every day for eight days. At the beginning and conclusion of the study, analyses of water quality such as Total Organic Matter, NH3-N, and NO2-N, were made. The findings revealed that treatment F seemed to have the best survival rate (85.0%) and positive control had the lowest survival rate (0%). (treatment G). The shrimp were more resistant to WSSV due to the longer immersion in the herbal extracts.

Physiological and gene expression responses of diploid and triploid Pacific oyster ( Crassostrea gigas ) to heat acclimation

High temperature is considered to be one of the important causes of mass mortality of diploid and triploid oysters in summer. In order to compare the tolerance adaptability of diploid and triploid oysters to heat stress, the activities of superoxide dismutase activity (SOD), catalase activity (CAT) and contents of malondialdehyde (MDA) and the expression of Hsp70 and metallothionein (MT) genes in diploid and triploid oysters under acute and chronic heat stress were studied. The results showed that the survival rate of diploid oysters was significantly higher than that of triploid oysters under acute and chronic heat stress (p < 0.05). Under acute heat stress, the SOD levels in gills of both diploid and triploid oysters increased significantly from hour 3 (p < 0.05), but there was no significant difference in SOD levels between diploid and triploid oysters at all time points. The SOD level in hepatopancreas of triploid oysters was significantly higher than that of diploid oysters at all time points except 48 h (p < 0.05). The CAT level of diploid and triploid oysters decreased sharply at 48 h and that of diploid oysters was significantly higher than that of triploid oysters (p < 0.05). Under acute heat stress, the increase in MDA content in triploid oysters was significantly higher than that in diploid oysters (p < 0.05). Under acute heat stress, the expression levels of Hsp70 in the gills and hepatopancreas were significantly increased in diploid and triploid oysters (p < 0.05), but increased varies between gills and hepatopancreas. The expression levels of MT in the gills and hepatopancreas were significantly decreased in diploid and triploid oysters (p < 0.05). The results obtained in this study provide physiological and immunological evidence to explain differences in high-temperature tolerance between diploid and triploid oysters and help us better understand the mass mortality of oysters that occurs during high temperatures in summer.

Molecular characterization and phylogenetic analysis of parasitic copepoda; Ergasilus sieboldiisolated from cultured gilthead sea bream (Sparus aurata) in Egypt, associated with analysis of oxidative stress biomarkers.

Parasitic copepods are common damaging ectoparasites of cultured marine fish that induce high mortalities in fish farms. The present study aimed to identify the cause of mass mortalities of cultured gilthead sea bream (Sparus aurata) as one of the highly valuable cultured marine fish species in Egypt. Parasitological examination demonstrated Ergasilus sieboldin (E. sieboldi) adult females of (1.3 ± 0.01mm, n = 55) mean body length and (0.53 ± 0.04mm) body width, lodged in the gill filaments of the forty examined fish with a pair of strong clawed antennae. The detected parasite has six segmented antennules and consists of cephalosome followed by four divided thoracic segments that narrow posteriorly, five pairs of swimming legs, genital segment, abdominal segments followed by furcal rami with unequal caudal setae and two egg sacs at the end of the body. The collected E. sieboldi were confirmed by molecular characterization and phylogenetic analysis based on 28S rDNA sequencing. The obtained sequence in this study was registered in the GenBank with (OM812074) accession number as a first sequence of E. sieboldi from Egypt. Oxidative stress biomarkers in the gills of the parasitized fish were evaluated to describe the host defense mechanisms against E. sieboldi infestation. The current study demonstrated decreasing in reduced glutathione (GSH) content and activity of the anti-oxidant enzyme catalase (CAT), as well as elevation in the level of malondialdehyde (MDA) due to exposure to oxidative damage that might have a role in the tissue damage and dysfunction.

A case report of interspecies transmission of nervous necrosis virus (NNV) between red seabream brood (Pagrus major) and juvenile Pacific cod (Gadus macrocephalus)

The viral infectious disease called viral nervous necrosis (VNN) or viral encephalopathy and retinopathy (VER) is a particularly lethal virus for larvae and juvenile fish, and seven genotypes have been reported thus far. These viruses are capable of both vertical and horizontal transmission. In this study, molecular biological and histopathological analyses were performed to determine the cause of mass mortality in juvenile Pacific cod (Gadus macrocephalus), which began to feed on red seabream (Pagrus major) eggs. Vacuolization, one of the characteristic symptoms of VNN, was confirmed in the brain and eyes of brood red seabream (P. major) and juvenile Pacific cod (G. macrocephalus). In addition, the inclusion body-like structure was confirmed in the electron microscopic analysis of the gonads and eggs of brood red seabream (P. major). In molecular biological analysis, the target bands were also found in the brain, kidney, liver, spleen, gonad (P. major brood only), and egg (P. major brood only). This vertical/horizontal interspecies transmission needs to be controlled with particular care when producing seedlings, considering that seedlings can be produced for release for the creation or recovery of aquatic resources in addition to aquaculture.

Rabies as a Potential Cause of Mass Mortality Events in North American Bat Species.

Rabies-association bat mortality events are rarely reported, suggesting that rabies is not a significant cause of bat mass mortality. Three bat die-offs in National Park Service units were attributed to rabies, highlighting the value of including rabies, and rabies virus strain spillover events, as a differential in mass mortality events.

CRISPR/Cas9-mediated generation of auxotrophic Edwardsiella piscicida mutants and immunization in olive flounder (Paralichthys olivaceus)

Edwardsiella piscicida has been a cause of mass mortality in cultured fish. In this study, to produce auxotrophic E. piscicida mutants, a CRISPR/Cas9 system was used instead of the traditional sacB-based allelic exchange method. Under the optimal CRISPR engineering condition, we could efficiently produce either alr or asd gene knockout E. piscicida auxotrophic mutants, and this genome editing process was much simpler and faster than the allelic exchange method. The simultaneous knockout of double auxotrophic genes (alr and asd) and the insertion of a foreign gene expression cassette in E. piscicida chromosome were also successfully performed using the established CRISPR/Cas9 system. Furthermore, to enhance the possibility to get permission as a commercial vaccine, we produced an auxotrophic E. piscicida mutant having only one nucleotide-deleted alr gene (E. piscicida △alr-1). Olive flounder (Paralichthys olivaceus) fingerlings immunized with 1 × 106 and 1 × 105 CFU/fish of E. piscicida △alr-1 showed the superior ability in the induction of serum agglutination activity and in the protection against E. piscicida compared to killed E. piscicida. However, olive flounder immunized with 1 × 107 CFU/fish of E. piscicida △alr-1 showed high mortality far before the challenge, and the isolated E. piscicida from moribund and dead fish had the wild type alr gene, suggesting the reversion of one base-deleted alr gene to original form by a second mutation in olive flounder. Therefore, investigation on the minimum number of edited nucleotide for stable maintenance of E. piscicida mutants should be further conducted.

A Novel Gonadotropic Microsporidian Parasite (Microsporidium clinchi n. sp.) Infecting a Declining Population of Pheasantshell Mussels (Actinonaias pectorosa) (Unioinidae) from the Clinch River, USA

Freshwater mussels of the order Unionida are among the most endangered animal groups globally, but the causes of their population decline are often enigmatic, with little known about the role of disease. In 2018, we collected wild adult pheasantshell (Actinonaias pectorosa) and mucket (Actinonaias ligamentina) during an epidemiologic survey investigating an ongoing mussel mass mortality event in the Clinch River, Virginia and Tennessee, USA. Histopathology and transmission electron microscopy showed a novel microsporidian parasite primarily infecting the ovary of pheasantshell. Sequencing of the small subunit rRNA gene produced a 1333 bp sequence with the greatest similarity to Pseudonosema cristatellae (AF484694.1; 86.36%; e-value = 0), a microsporidium infecting the freshwater bryozoan (Cristatella mucedo). Microsporidia were observed in 65% (17/26) of the examined female pheasantshell (A. pectorosa) and in no (0/2) female muckets (A. ligamentina) and occurred at mortality and non-mortality sites. Our findings indicate that a novel parasite, Microsporidium clinchi n. sp., is present in pheasantshell in the Clinch River, and while likely not a cause of mass mortality, could reduce fecundity and recruitment in this declining population and threaten the success of reintroductions. Surveillance of M. clinchi n. sp. and evaluation of broodstock and their progeny for microsporidia would therefore be prudent.

The antibiotic use by pregnant mice was a reason of lung pathology of their offspring

The inappropriate antibiotic usage in human and animal treating is a main reason of the antibiotic resistance, spreading wider and wider all over the world. It was proved that the use of antibiotic induces the changes in microbiota profile as well as the protective properties of the intestinal mucosal barrier, determining the level of the bacterial translocation to the distant loci of the body. Pneumonia in newborns is one of the severe pathologies that cause increased neonatal morbidity and mortality. During the newborn period, pneumonia develops much more often than in other age periods. It is considered that main reason of respiratory adaptation disorders and newborns’ pneumonia is the intrauterine infection and the development of the inflammatory process. In animal husbandry we can see that a non- specific bronchopneumonia is one of the main causes of mass mortality of young cattle. There is no any confirmed reason of the growing level of the mortality of cattle. Here we present the results of our investigation which allow suggesting a role of antibiotic use by pregnant females as a basis for the following bacterial translocation to the fetus and a non- specific bronchopneumonia.

MULTIPLE EPIDEMICS IN AUSTRIAN FRINGILLIDAE CAUSED BY A SINGLE VARIANT OF SALMONELLA TYPHIMURIUM.

In Austria, numerous deaths of wild birds of the order Passeriformes, family Fringillidae, occurred during the winter months of 2010 and 2012. The Eurasian Siskin (Carduelis spinus) was the species most often affected. The dead birds were mainly found in the immediate vicinity of feeding places. Vigilant citizens sent birds (n=34) for pathologic examination to the Institute of Pathology in Vienna, Austria. All birds were cachectic or in a very poor nutritional condition. At gross examination, the most striking findings were multifocal to confluent, yellow-white nodules in the crop or esophageal mucosa. In histologically examined birds (n=24), severe transmural fibrino-purulent to necrotizing ingluviitis or esophagitis with large amounts of intralesional bacteria was observed. Bacteriologic examination of crop, liver, or other organs from 14 birds revealed abundant growth of Salmonella serovar Typhimurium (antigenic formula 1,4,5,12:i:1,2; phage type U277) in all individuals. By means of immunohistochemistry, these bacteria were detected not only in crop mucosa but also in lung tissue. In 17 birds (71%), structures morphologically resembling Macrorhabdus ornithogaster were detected histologically on the surface of the proventricular epithelium. Thus, the cause of mass mortality of the passerine birds was identified as infection with Salmonella Typhimurium, which was associated with growth of presumed M. ornithogaster in many cases.

Controlled Infection Experiment With Aphanomyces astaci Provides Additional Evidence for Latent Infections and Resistance in Freshwater Crayfish

For 150 years the crayfish plague disease agentAphanomyces astacihas been the cause of mass mortalities among native European crayfish populations. However, recently several studies have highlighted the great variability ofA. astacivirulence and crayfish resistance toward the disease. The main aim of this study was to compare the response of two crayfish species, the European native noble crayfish (Astacus astacus) and the invasive alien marbled crayfish (Procambarus virginalis), to anA. astacichallenge with a highly virulent strain from haplogroup B and a lowly virulent strain from haplogroup A. In a controlled infection experiment we showed a high resistance of marbled crayfish against anA. astaciinfection, with zoospores from the highly virulent haplogroup B strain being able to infect the crayfish, but unable to cause signs of disease. Furthermore, we demonstrated a reduced virulence in theA. astacistrain belonging to haplogroup A, as shown by the light symptoms and the lack of mortality in the generally susceptible noble crayfish. Interestingly, in both marbled crayfish and noble crayfish challenged with this strain, we observed a significant decrease of the detected amount of pathogen’s DNA during the experiment, suggesting that thisA. astacihaplogroup A strain has a decreased ability of penetrating into the cuticle of the crayfish. Our results provide additional evidence of how drastically strains belonging toA. astacihaplogroup B and haplogroup A differ in their virulence. This study confirmed the adaptation of one specificA. astacihaplogroup A strain to their novel European hosts, supposedly due to reduced virulence. This feature might be the consequence ofA. astaci’s reduced ability to penetrate into the crayfish. Finally, we experimentally showed that marbled crayfish are remarkably resistant against the crayfish plague disease and could potentially be latently infected, acting as carriers of highly virulentA. astacistrains.

Influence of intensive net cage farming on hydrodynamic and geochemical environmental conditions and the mass mortality of abalone in South Korea

The abalone aquaculture industry in South Korea has grown rapidly since the 2000s. In this study, we investigated the sedimentary pollution at four major abalone farms responsible for ~60% of all South Korean abalone produced. We also surveyed the current statuses of cage facilities, abalone mass mortality, and current velocities within and outside farm cages. The concentrations of total organic carbon in the study area were 7.92 ± 2.09 mg g−1, indicating a mild level of sedimentary pollution. We observed higher mortality rates in rectangular-shaped shelter cages than in triangular shelters. With increases in the number and size of abalone farming facilities, current velocities inside the cages declined by an average of 45% relative to those outside the cages, leading to poor habitat conditions for farmed abalone. Our results provide insights into the current status of the benthic environments and major causes of mass mortality in the abalone farms of South Korea.

Histopathology and oxidative stress responses of Nile tilapia Oreochromis niloticus exposed to temperature shocks

Temperature shock is a major natural cause of mass mortality of global fish. Nile tilapia Oreochromis niloticus, one of the most widely cultured species, with high resistance against severe environmental conditions, is also affected by rapid temperature changes. This research was conducted to investigate histopathological changes and oxidative stress in O. niloticus in response to temperature shock. The malondialdehyde levels in the serum, gills and brain, the histopathology of the gills and brain, and the histochemical characterization of the gills’ mucosubstances were measured in the fish exposed to heat shock and cold shock conditions. The results showed that the fish could not survive under 37 °C for 24 hours. Malondialdehyde levels in the gills, brain and serum increased significantly when compared to those of the controls. Moreover, histopathological changes and a decrease in the number of neutral and acidic mucous cells was observed in the gills of fish in both the heat shock and cold shock groups. Histopathological alteration, vacuolated neuropil in the brain, was observed only in the fish in the cold shock groups. The results from this study indicate that rapid 4 °C changes in water temperature (25–21 and 25–29 °C) evoked oxidative stress and histological damage to O. niloticus, whereas extreme 12 °C changes (25–13 and 25–37 °C) severely affected their oxidative stress and histopathological condition.

FROM DARK TO LIGHT AND BACK AGAIN: IS PINNA NOBILIS, THE LARGEST MEDITERRANEAN BIVALVE, ON THE BRINK OF EXTINCTION?

Pinna nobilis&nbsp;is the largest bivalve of the Mediterranean Sea, where it represents&nbsp;a flagship species. As a possible consequence of several human disturbing activities, at the beginning of ‘80s, populations of fan mussel started a severe demographic decline. To reverse this trend, P. nobilis&nbsp;was included in a regime of full protection which led to a significant recovery of the species at the beginning of the millennium. Unfortunately, P. nobilis&nbsp;is presently facing a dramatic epidemic, which is bringing this species to the brink of extinction. This phenomenon started in early autumn 2016, from the Mediterranean coasts of Spain. Since then, the mass mortality spread quickly eastward reaching almost all Mediterranean areas. First epidemiological surveys ascribed the mass mortality of P. nobilis&nbsp;to the protozoan Haplosporidium pinnae,&nbsp;but recent studies indicated some species of bacteria belonging to the genera Mycobacterium&nbsp;and Vibrio as further or alternative etiological agents. Presently, a multifactorial disease mediated by the combined action of several pathogens seems to be the most probable responsible factor which is favouring the phenomenon. Despite the conservational prominence of P. nobilis, a low number of studies investigated the genetic structure of this species before its mass mortality and all were consistent in evidencing a very good health for populations throughout the whole Mediterranean, pointing out high levels of genetic variability and good genetic connectivity among areas. Now it would be useful to provide an extended molecular survey post-epidemic, for a deeper understanding of the causes of mass mortality of fan mussels.