Influence of environmental temperature on the immune response in fish

Mediterranean Aquaculture in a Changing Climate: Temperature Effects on Pathogens and Diseases of Three Farmed Fish Species

Climate change is expected to have a drastic effect on aquaculture worldwide. As we move forward with the agenda to increase and diversify aquaculture production, rising temperatures will have a progressively relevant impact on fish farming, linked to a multitude of issues associated with fish welfare. Temperature affects the physiology of both fish and pathogens, and has the potential to lead to significant increases in disease outbreaks within aquaculture systems, resulting in severe financial impacts. Significant shifts in future temperature regimes are projected for the Mediterranean Sea. We therefore aim to review and discuss the existing knowledge relating to disease outbreaks in the context of climate change in Mediterranean finfish aquaculture. The objective is to describe the effects of temperature on the physiology of both fish and pathogens, and moreover to list and discuss the principal diseases of the three main fish species farmed in the Mediterranean, namely gilthead seabream (Sparus aurata), European seabass (Dicentrarchus labrax), and meagre (Argyrosomus regius). We will attempt to link the pathology of each disease to a specific temperature range, while discussing potential future disease threats associated with the available climate change trends for the Mediterranean Sea.

Seroconversion and Skin Mucosal Parameters during Koi Herpesvirus Shedding in Common Carp, Cyprinus carpio

Seroconversion and the mucosal lysozyme G (lysG), complement 3 (c3), and immunoglobulins M (IgMsec) and Z2 (IgZ2) were measured for up to 900 degree days (DD) in skin swabs from common carp exposed to koi herpesvirus (KHV or CyHV-3) at either a non-permissive temperature (12 °C) or permissive temperatures (17 and 22 °C), and in survivors subjected to temperature increase to 22 °C 500 DD after the initial exposure. The survival rate at 22 °C varied from 100% in fish initially exposed at 12 °C, to 20% at 17 °C and 0% at 22 °C. Viral shedding episodes lasted for up to 29 days (493 DD) for fish clinically infected at 17 °C, and up to 57 days (684 DD) for asymptomatic fish held at 12 °C. Up-regulation of lysG transcripts was measured at 17 and 22 °C. Down-regulation of c3 and IgMsec transcripts was measured independent of the water temperature, followed by up-regulation after the temperature increase coinciding with seroconversion and clearance of KHV from the skin mucus. IgZ2 mRNA showed a negative correlation with IgM transcripts. KHV subversion of the complement system at the mucosal site coupled with poor immunoglobulin secretion during the viral replication might contribute to the long window of viral shedding, thus facilitating viral transmission.

Intramuscular DNA Vaccination of Juvenile Carp against Spring Viremia of Carp Virus Induces Full Protection and Establishes a Virus-Specific B and T Cell Response

Although spring viremia of carp virus (SVCV) can cause high mortalities in common carp, a commercial vaccine is not available for worldwide use. Here, we report a DNA vaccine based on the expression of the SVCV glycoprotein (G) which, when injected in the muscle even at a single low dose of 0.1 µg DNA/g of fish, confers up to 100% protection against a subsequent bath challenge with SVCV. Importantly, to best validate vaccine efficacy, we also optimized a reliable bath challenge model closely mimicking a natural infection, based on a prolonged exposure of carp to SVCV at 15°C. Using this optimized bath challenge, we showed a strong age-dependent susceptibility of carp to SVCV, with high susceptibility at young age (3 months) and a full resistance at 9 months. We visualized local expression of the G protein and associated early inflammatory response by immunohistochemistry and described changes in the gene expression of pro-inflammatory cytokines, chemokines, and antiviral genes in the muscle of vaccinated fish. Adaptive immune responses were investigated by analyzing neutralizing titers against SVCV in the serum of vaccinated fish and the in vitro proliferation capacity of peripheral SVCV-specific T cells. We show significantly higher serum neutralizing titers and the presence of SVCV-specific T cells in the blood of vaccinated fish, which proliferated upon stimulation with SVCV. Altogether, this is the first study reporting on a protective DNA vaccine against SVCV in carp and the first to provide a detailed characterization of local innate as well as systemic adaptive immune responses elicited upon DNA vaccination that suggest a role not only of B cells but also of T cells in the protection conferred by the SVCV-G DNA vaccine.

Spectral imaging of red blood cells in experimental anemia of Cyprinus carpio

In the present work we have studied the effect of experimental anemia induced at both low and optimal temperatures on erythropoiesis in Cyprinus carpio. The results showed that hemoglobin concentration per cell was similar in both temperature conditions, however, red blood cell (RBC) concentration was higher at the optimal temperature. Induced anemia caused an abrupt decrease in RBC concentration, while the hemoglobin concentration per cell remained unchanged. Recovery, as shown by electron microscopy, was characterized by the release of differentiating young and intermediate cells to the peripheral blood. It was revealed that with the progression of differentiation the nucleus/cytoplasm ratio decreases, the chromatin condenses and the shape of the nucleus changes from round to elliptical. Spectral imaging revealed an increase in the optical density of chromatin with the maturation of the cells. The chromatin that was dispersed over the nuclear volume in the young cells becomes highly ordered in the mature cells. Spectral similarity mapping revealed the formation of a novel structure of high symmetry, representing chromatin rearrangement during the process of cellular differentiation.

Possible mechanisms responsible for the reduced intestinal flora in hibernating leopard frogs (Rana pipiens)

Mechanisms and factors that normally control the large intestinal flora were investigated to determine whether changes in these parameters could account for the decreased bacterial concentration and facultative nature of the flora found in hibernating frogs. It appeared that low temperatures and limited nutrients were the main factors responsible for the decrease in the bacterial concentration and may also have been responsible for the increase in the proportions of facultative organisms, since no change in the redox potential was seen. The hibernating frogs were extremely sluggish in the removal of India ink particles from the circulatory system by the Kupffer cells of the liver compared with nonhibernating frogs. They were unable to mount an antibody response to bovine serum albumin, but their serum did exhibit killing of Pseudomonas paucimobilis, suggesting opsonization by preformed antibody and complement. The role of these host factors in protecting the hibernating frog against this indigenous flora is discussed.