With the worldwide increase of fisheries, fish wastes have had a similar increase, alternatively they can be seen as a source of novel substances for the improvement of society’s wellbeing. Elasmobranchs are a subclass fished in high amounts, with some species being mainly bycatch. They possess an endoskeleton composed mainly by cartilage, from which chondroitin sulfate is currently obtained. Their use as a viable source for extraction of type II collagen has been hypothesized with the envisaging of a biomedical application, namely in biomaterials production. In the present work, raw cartilage from shark (Prionace glauca) and ray (Zeachara chilensis and Bathyraja brachyurops) was obtained from a fish processing company and submitted to acidic and enzymatic extractions, to produce acid-soluble collagen (ASC) and pepsin-soluble collagen (PSC). From all the extractions, P. glauca PSC had the highest yield (3.5%), followed by ray ASC (0.92%), ray PSC (0.50%), and P. glauca ASC (0.15%). All the extracts showed similar properties, with the SDS-PAGE profiles being compatible with the presence of both type I and type II collagens. Moreover, the collagen extracts exhibited the competence to maintain their conformation at human basal temperature, presenting a denaturation temperature higher than 37 °C. Hydrogels were produced using P. glauca PSC combined with shark chondroitin sulfate, with the objective of mimicking the human cartilage extracellular matrix. These hydrogels were cohesive and structurally-stable at 37 °C, with rheological measurements exhibiting a conformation of an elastic solid when submitted to shear strain with a frequency up to 4 Hz. This work revealed a sustainable strategy for the valorization of fisheries’ by-products, within the concept of a circular economy, consisting of the use of P. glauca, Z. chilensis, and B. brachyurops cartilage for the extraction of collagen, which would be further employed in the development of hydrogels as a proof of concept of its biotechnological potential, ultimately envisaging its use in marine biomaterials to regenerate damaged cartilaginous tissues.

Increasing temperature due to climate change may represent an important factor influencing the physiology of organisms, with potential impacts on the ecosystem, especially to ectotherms, which include most aquatic species that are highly sensitive to environmental temperature changes. However, in nature there is a multitude of factors influencing an organism at a given time with regard to fitness, while single stressor scenarios are far from ecologically relevant scenarios. The interaction of different stressors, biotic and/or abiotic, can have synergistic or antagonistic effects for the organism, which finally can lead to different states of overall fitness and eventually influence the whole population dynamics. Besides the common abiotic factors affecting organisms, biotic factors (such as inter- and intra-species interaction) ought to be considered when assessing organisms’ responses in a given situation, as they are key events affecting organisms’ dynamics. This study focused on the effects of water temperature increase and predation stress (octopus) on the metabolism of an intertidal rock pool fish, the rock goby (Gobius paganellus), while also addressing the potential interaction of these stressors. Groups of individuals were exposed to simulated predation stress, and temperature increase of 1 °C d-1 from 20 °C up to 29 °C, and also to both stressors combined. Treatment groups were compared with control (20 °C). To get a detailed insight on how both stressors affect these organisms, effects at both whole organismal level (growth and respiration) and cellular level (biochemical biomarkers) were estimated. Therefore, growth, energy available (Ea - total lipids, carbohydrates, and protein), energy consumed (Ec – measuring electron transfer system activity), cellular energy allocation (CEA), energy metabolism related enzyme activities (lactate dehydrogenase-LDH and isocitrate dehydrogenase-IDH), detoxification and oxidative stress responses and consequences (glutathione s-transferase-GST, superoxide dismutase-SOD, catalase-CAT, DNA damage, and lipid peroxidation-LPO) in muscle, gill, and liver tissue, considering both short-term exposure and long-term acclimation, were investigated. In addition, oxygen consumption rates of single fish were measured to establish standard and routine metabolic rates of G. paganellus, and the potential influence of simulated predation risk. Results show a growth decline as a result of all treatments compared to control, and also effects on the assessed biochemical parameters for both temperature and predation risk stressors. This leads to the presumption of physiological changes due to these stressors, and at the same time the stressor individual effects and their potential interaction in the biomarkers are highlighted in this work, while the relevance of these findings are discussed concerning real multi-stressor scenarios.

Marine biodiversity is being threatened by the increased uptake of atmospheric CO2, known as ocean acidification. Although the majority of literature points to negative and abnormal effects to future acidification scenarios in short term exposures, most fail to evaluate and recognize the potential adaptation capacity and its effects among populations and species. Here, the effects and the capacity of the sand smelt larvae Atherina presbyter to respond to different pCO2 levels (control: ~600 μatm, pH = 8.03; medium: ~1000 μatm, pH = 7.85; high: ~1800 μatm, pH = 7.64) were measured, addressing larval development characteristics, oxidative stress, and energy metabolism. Recently, Silva et al. (2016) demonstrated that the exposure of these larvae to increasing levels of pCO2, leads to higher energetic costs and morphometric changes, and points to a decrease in the antioxidant response capacity. However, in that study, larvae were exposed to only a short 15-days period. In the present study we aim at: 1) investigating the potential of sand smelt larvae to acclimate to acidification conditions by exposing larvae to increasing CO2 levels for 45 days; 2) determine the ability of sand smelt larvae to recover from stressful conditions induced by exposure to high CO2 levels. Individuals were collected at the coastal area of the Arrábida Marine Park (Portugal), transported to the laboratory and randomly assigned and exposed to three different pCO2 levels. After 30 days of exposure, larvae were either switched between treatments or left in the original treatment for another 15 days. Larvae were randomly sampled at 0, 15, 30, and 45 days, photographed for morphometric analysis, weighed, and stored at -80ºC until biochemical analysis were performed. The biochemical biomarkers measured were related with: 1) oxidative stress and damage: superoxide dismutase and catalase enzyme activities, as well as lipid peroxidation and DNA damage levels; and 2) energy metabolism: total carbohydrate, protein and lipid levels as measures of available energy; electron transfer system activity as a measure of oxygen and energy consumption; cellular energy allocation; and lactate dehydrogenase and isocitrate dehydrogenase enzyme activities. Results suggest particular sensitivity of sand smelt to increasing levels of pCO2 seen by the alteration in their global energetic status and by the oxidative stress effects. The results contribute simultaneously to an integrative view of the ocean acidification effects and adaptation capacity of this species during environmental stress.