The ontogeny of lymphoid organs and IgM+ B-cells in ballan wrasse (Labrus bergylta) reveals a potential site for extrarenal B-cell lymphopoiesis: The pancreas.

Vaccination of farmed fish is the most effective prophylactic measure against contagious diseases but requires specific knowledge on when the adaptive immune system is fully developed. The present work describes kidney and spleen morphogenesis as well as B-cell development in the ballan wrasse (Labrus bergylta). The kidney was present at hatching (0 days pot hatching, dph) but was not lymphoid before larvae was 50-60 dph (stage 5), containing abundant Igµ+ cells. The spleen anlage was first observed in larvae at 20-30 dph and was later populated with B-cells. Unexpectedly, we found strong RAG1 signal together with abundant Igµ+ and IgM + cells in the exocrine pancreas of larvae from when the kidney was lymphoid and onwards, suggesting that B-cell lymphopoiesis occurs not only in the head kidney (HK) but also in pancreatic tissue. In this agastric fish, the pancreas is diffused along the intestine and the early presence of IgM+ B-cells in pancreatic tissue might have a role in maintain immune homeostasis in the peritoneal cavity, making a substantial contribution to early protection. IgM-secreting cells in HK indicate the presence of systemic IgM at stage 5, before the first IgM+ cells were identified in mucosal sites. This work together with our previous study on T-cell development in this species indicates that although T- and B-cells start to develop around the same time, B-cells migrate to mucosal tissues ahead of T-cells. This early migration likely involves the production of natural antibodies, contributing significantly to early protection. Moreover, a diet composed of barnacle nauplii did not result in an earlier onset of B-cell lymphopoiesis, as seen in the previous study analysing T-cell development. Nevertheless, components for adaptive immunity indicating putative immunocompetence is likely achieved in early juveniles (>100 dph). Additionally, maternal transfer of IgM to the offspring is also described. These findings provide important insights into the development of the immune system in ballan wrasse and lay the foundation for optimizing prophylactic strategies in the future. Furthermore, this work adds valuable information to broaden the knowledge on the immune system in lower vertebrates.

The thymus and T-cell ontogeny in ballan wrasse (Labrus bergylta) is nutritionally modelled.

Marine fish larvae often experience high mortality unrelated to predation during early life stages, and farmed ballan wrasse (Labrus bergylta) is no exception. Knowing when the adaptive immune system is developed and fully functional, and how nutrition may modulate these processes is therefore of importance to establish effective prophylactic measures and will also extend the relatively limited knowledge on the immune system in lower vertebrates. The thymus anlage of ballan wrasse was found to be histologically visible for the first time at larval stage 3 (20-30 days post hatch, dph) and becomes lymphoid at stage 5 (50-60 dph) correlating with an increase of T-cell marker transcripts. At this stage, a clear zonation into a RAG1+ cortex and a RAG1- CD3ϵ+ medulla was distinguished, indicating that T-cell maturation processes in ballan wrasse are similar to other teleosts. The higher abundance of CD4-1+ compared to CD8ß+ cells in the thymus together with the apparent lack of CD8ß+ cells in gill, gut, and pharynx, where CD4-1+ cells were identified, indicates that helper T-cells have a more prominent role during larval development compared to cytotoxic T-cells. As ballan wrasse lacks a stomach but has an exceptionally high IgM expression in the hindgut, we hypothesize that helper T-cells are crucial for activation and recruitment of IgM+ B-cells and possibly other leukocytes to the gut during early development. Nutritional factors such as DHA/EPA, Zn and Se may lead to an earlier expression of certain T-cell markers as well as a larger size of the thymus, indicating an earlier onset of adaptive immunity. Including live feeds that supplies the larva with higher amounts of these nutrients can therefore be beneficial for ballan wrasse farming.

Movement patterns of temperate wrasses (Labridae) within a small marine protected area.

The movement patterns of three commercially important wrasse (Labridae) species inside a small marine protected area (~ 0.15 km2 ) on the west coast of Norway were analysed over a period of 21 months. The mean distance between capture and recapture locations varied between 10 and 187 m, and was species and season specific. The extent of movement was not related to body size or sex. These results imply that a network of small strategically located marine protected areas can be used as management tools to protect wrasses from size- and sex-selective fishing mortality.

The planktonic stages of the salmon louse (Lepeophtheirus salmonis) are tolerant of end-of-century pCO2 concentrations.

The copepod Lepeophtheirus salmonis is an obligate ectoparasite of salmonids. Salmon lice are major pests in salmon aquaculture and due to its economic impact Lepeophtheirus salmonis is one of the most well studied species of marine parasite. However, there is limited understanding of how increased concentration of pCO2 associated with ocean acidification will impact host-parasite relationships. We investigated the effects of increased pCO2 on growth and metabolic rates in the planktonic stages, rearing L. salmonis from eggs to 12 days post hatch copepodids under three treatment levels: Control (416 µatm), Mid (747 µatm), and High (942 µatm). The pCO2 treatment had a significant effect on oxygen consumption rate with the High treatment animals exhibiting the greatest respiration. The treatments did not have a significant effect on the other biological endpoints measured (carbon, nitrogen, lipid volume, and fatty acid content). The results indicate that L. salmonis have mechanisms to compensate for increased concentration of pCO2and that populations will be tolerant of projected future ocean acidification scenarios. The work reported here also describes catabolism during the lecithotrophic development of L. salmonis, information that is not currently available to parameterize models of dispersal and viability of the planktonic free-living stages.

Exposure to teflubenzuron negatively impacts exploratory behavior, learning and activity of juvenile European lobster (Homarus gammarus).

Infestations with salmon lice, a parasitic copepod, is a major problem in the salmon farming industry. Teflubenzuron is an in-feed pharmaceutical applied to control lice outbreaks; the standard medication is 10 mg per kg fish per day for seven days. Surveys reveal that teflubenzuron accumulates and persists in the sediment around fish farms and causes deformities and mortality in juvenile European lobster (Homarus gammarus), a species commonly found in the vicinity of salmon farms in Norway. To date, there is no information on sub-lethal effects of teflubenzuron on, for example, behavior. We conducted an experiment to assess possible difference in the shelter seeking behavior of teflubenzuron-exposed (N = 19) vs. not exposed (N = 19) H. gammarus juveniles. The teflubenzuron-exposed juveniles had been given very low concentrations, 1.7 µg per pellet twice per week for 113 days prior to this experiment. The concentration of teflubenzuron was estimated to be less than 1 ng/g lobster when they were tested in the behavior experiment. Animals were placed in a lane with a shelter at one end. Once a lobster had found and entered the shelter, they were repeatedly displaced back to the opposite end of the lane, for a total of 3 repeated runs per animal. Three of the exposed juveniles failed to settle in the shelter, and the remaining teflubenzuron-exposed animals took significantly more time to explore the environment and to find and recognize shelter. Furthermore, exposed lobsters also exhibited slower walking speed compared to the controls. These results demonstrate that teflubenzuron significantly reduces exploratory behavior, learning and activity of juvenile H. gammarus. Thus, exposure to teflubenzuron could increase predation mortality of juvenile lobsters in the wild.

Glass eels (Anguilla anguilla) have a magnetic compass linked to the tidal cycle.

The European eel (Anguilla anguilla) has one of the longest migrations in the animal kingdom. It crosses the Atlantic Ocean twice during its life history, migrating between the spawning area in the Sargasso Sea and Europe, where it is widely distributed. The leptocephalus larvae drift with the Gulf Stream and other currents for more than a year and metamorphose into glass eels when they arrive on the continental shelf and move toward coastal areas. The mechanisms underlying glass eel orientation toward the coast and into freshwater systems are poorly known. However, anguillid eels, including the glass eel life stage, have a geomagnetic sense, suggesting the possibility that they use Earth's magnetic field to orient toward the coast. To test this hypothesis, we used a unique combination of laboratory tests and in situ behavioral observations conducted in a drifting circular arena. Most (98%) of the glass eels tested in the sea exhibited a preferred orientation that was related to the tidal cycle. Seventy-one percent of the same eels showed the same orientation during ebb tide when tested in the laboratory under a manipulated simulated magnetic field in the absence of any other cue. These results demonstrate that glass eels use a magnetic compass for orientation and suggest that this magnetic orientation system is linked to a circatidal rhythm.

Effect of sub-lethal exposure to ultraviolet radiation on the escape performance of Atlantic cod larvae (Gadus morhua).

UNLABELLED: The amount of ultraviolet (UV) radiation reaching the earth's surface has increased due to depletion of the ozone layer. Several studies have reported that UV radiation reduces survival of fish larvae. However, indirect and sub-lethal impacts of UV radiation on fish behavior have been given little consideration. We observed the escape performance of larval cod (24 dph, SL: 7.6±0.2 mm; 29 dph, SL: 8.2±0.3 mm) that had been exposed to sub-lethal levels of UV radiation vs. unexposed controls. Two predators were used (in separate experiments): two-spotted goby (Gobiusculus flavescens; a suction predator) and lion's mane jellyfish (Cyanea capillata; a "passive" ambush predator). Ten cod larvae were observed in the presence of a predator for 20 minutes using a digital video camera. Trials were replicated 4 times for goby and 5 times for jellyfish. Escape rate (total number of escapes/total number of attacks ×100), escape distance and the number of larvae remaining at the end of the experiment were measured. In the experiment with gobies, in the UV-treated larvae, both escape rate and escape distance (36%, 38±7.5 mm respectively) were significantly lower than those of control larvae (75%, 69±4.7 mm respectively). There was a significant difference in survival as well (UV: 35%, CONTROL: 63%). No apparent escape response was observed, and survival rate was not significantly different, between treatments (UV: 66%, CONTROL: 74%) in the experiment with jellyfish. We conclude that the effect and impact of exposure to sub-lethal levels of UV radiation on the escape performance of cod larvae depends on the type of predator. Our results also suggest that prediction of UV impacts on fish larvae based only on direct effects are underestimations.

Grazing rates of Calanus finmarchicus on Thalassiosira weissflogii cultured under different levels of ultraviolet radiation.

UVB alters photosynthetic rate, fatty acid profiles and morphological characteristics of phytoplankton. Copepods, important grazers of primary production, select algal cells based upon their size, morphological traits, nutritional status, and motility. We investigated the grazing rates of the copepod Calanus finmarchicus on the diatom Thalassiosira weissflogii cultured under 3 levels of ultraviolet radiation (UVR): photosynthetically active radiation (PAR) only (4 kJ-m(-2)/day), and PAR supplemented with UVR radiation at two intensities (24 kJ-m(-2)/day and 48 kJ-m(-2)/day). There was no significant difference in grazing rates between the PAR only treatment and the lower UVR treatment. However, grazing rates were significantly (∼66%) higher for copepods feeding on cells treated with the higher level of UVR. These results suggest that a short-term increase in UVR exposure results in a significant increase in the grazing rate of copepods and, thereby, potentially alters the flow rate of organic matter through this component of the ecosystem.