Respiratory Physiology of European Plaice (<i>Pleuronectes platessa</i>) Exposed to <i>Prymnesium parvum</i>

During the last century, the blooms of the toxic haptophyte Prymnesium parvum have been responsible for massive fish kills in both aquaculture and wild populations. Despite decades of research, the ichthyotoxic properties of P. parvum, and how this alga affects fish, is still debated. Using a novel device to measure the respirometry, ventilation volume, ventilation frequency, oxygen extraction, and oxygen consumption of undisturbed European plaice (Pleuronectes platessa) were acquired during exposure to two algal species as well as hypoxia. Fourteen fish (258 &#177; 44 g) were initially exposed to severe hypoxia and left to recover for at least 48 h. Half of these fish were then exposed to known harmful concentrations of P. parvum (median &#177; standard deviation (SD); 2.6 &#215; 105 &#177; 0.6 &#215; 105 cells mL&#8722;1), while the remaining half were exposed to the non-toxic alga Rhodomonas salina (median &#177; SD; 3.2 &#215; 105 &#177; 0.7 &#215; 105 cells mL&#8722;1). During exposure to severe hypoxia, all of the fish were able to maintain oxygen consumption by increasing the ventilation volume. The results from fish that were exposed to P. parvum showed a significant decrease in oxygen extraction (median &#177; SD; 52.6 &#177; 6.9 percentage points) from pre-exposure to the end of the experiment, as opposed to fish exposed to R. salina, which were unaffected. These results indicate that suffocation affects the European plaice when exposed to P. parvum. The observed severe decrease in oxygen extraction can be ascribed to either damage of the gill epithelia or increased mucus secretion on the gills, as both would limit the transfer of oxygen, and both have been observed

Assessing the reproductive biology of the Greenland shark (Somniosus microcephalus)

The Greenland shark (Somniosus microcephalus, Squaliformes: Somniosidae) is a long-lived Arctic top predator, which in combination with the high historical and modern fishing pressures, has made it subject to increased scientific focus in recent years. Key aspects of reproduction are not well known as exemplified by sparse and contradictory information e.g. on birth size and number of pups per pregnancy. This study represents the first comprehensive work on Greenland shark reproductive biology based on data from 312 specimens collected over the past 60 years. We provide guidelines quantifying reproductive parameters to assess specific maturation stages, as well as calculate body length-at-maturity (TL50) which was 2.84±0.06 m for males and 4.19±0.04 m for females. From the available information on the ovarian fecundity of Greenland sharks as well as a meta-analysis of Squaliform reproductive parameters, we estimate up to 200–324 pups per pregnancy (depending on maternal size) with a body length-at-birth of 35–45 cm. These estimates remain to be verified by future observations from gravid Greenland sharks

Greenland Shark (<i>Somniosus microcephalus</i>) Stomach Contents and Stable Isotope Values Reveal an Ontogenetic Dietary Shift

Current knowledge on the feeding ecology of the Greenland shark (Somniosus microcephalus), a potential top predator in arctic marine ecosystems, is based on small sample sizes as well as narrow size ranges of sharks. Therefore, potential size-related feeding patterns remain poorly documented. Using stomach content data (N = 88) and stable isotope values of white muscle tissue (N = 40), this study evaluates the diet of sharks ranging in size from 81 to 474 cm (total length). The importance of prey categories (“Fish,” “Mammal,” “Squid,” “Crustacean,” and “Other”) was evaluated based on the reconstructed prey biomass of the stomach contents. Stable isotope values of δ13C and δ15N ranged between -14.4 to -19.9‰ and 11.8 to 17.2‰, respectively. The importance of each prey category was estimated by the Index of Relative Importance (IRI). Our findings suggest that the smallest Greenland sharks (200 cm) mainly feed on higher trophic level prey such as seals, epibenthic and benthic fishes including gadoids (Gadidae), skates (Rajidae), righteye flounders (Pleuronectidae), lumpfish (Cyclopteridae), wolffish (Anarhichadidae), and redfish (Sebastidae). Redfish were, however, only found to be important in the largest sharks sampled (>400 cm). In addition to demonstrating ontogenetic shifts in their feeding preferences, this study supports that Greenland sharks are capable of active predation on fast swimming seals and large fishes