Offshore aquaculture has gained momentum in recent years, and the production of an increasing number of marine fish species is being relocated offshore. Initially, predictions of the advantages that offshore aquaculture would present over nearshore farming were made without enough science‐based evidence. Now, with more scientific knowledge, this review revisits past predictions and expectations of offshore aquaculture. We analysed and explained the oceanographic features that define offshore and nearshore sites. Using Atlantic salmon (Salmo salar) as a case study, we focussed on sea lice, amoebic gill disease, and the risk of harmful algal blooms, as well as the direct effects of the oceanography on the health and physiology of fish. The operational and licencing challenges and advantages of offshore aquaculture are also considered. The lack of space in increasingly saturated sheltered areas will push new farms out to offshore locations and, if appropriate steps are followed, offshore aquaculture can be successful. Firstly, the physical capabilities of the farmed fish species and infrastructure must be fully understood. Secondly, the oceanography of potential sites must be carefully studied to confirm that they are compatible with the species‐specific capabilities. And, thirdly, an economic plan considering the operational costs and licencing limitations of the site must be developed. This review will serve as a guide and a compilation of information for researchers and stakeholders.

For decades, disruption of the bilateral symmetry of body structures has been related to underperformance and, hence, to fitness. In fish, this concept coupled with the claimed evidence for increased fluctuating asymmetry (FA) of pairs of hard structures, such as otoliths under conditions of stress, has led to the use of otolith FA (OFA) as a proxy for individual fitness and population success. Interpreting those significant differences in OFA in relation to stress-inducing environments and using them to identify suboptimal conditions for survival is especially appealing in the context of, for example, assessing climate change using historical otolith collections. Despite several works that give evidence to support the usefulness of OFA approach, we report on a number of unpublished and published datasets from a wide range of both, wild populations and experimental designs that show no correlation between OFA and any of the usual indicators of fitness or between OFA and expected stress gradients. Our results suggest that there may be a strong bias in the published literature towards positive relationships, despite the enormous importance of negative results for understanding the significance of OFA. These results might shed light on the interpretability of OFA in both laboratory and field studies.

The sea-run phenotype of rainbow trout (Oncorhynchus mykiss), like other anadromous salmonids, present a juvenile stage fully adapted to life in freshwater known as parr. Development in freshwater is followed by the smolt stage, where preadaptations needed for seawater life are developed making fish ready to migrate to the ocean, after which event they become post-smolts. While these three life stages have been studied using a variety of approaches, proteomics has never been used for such purpose. The present study characterised the blood plasma proteome of parr, smolt and post-smolt rainbow trout using a gel electrophoresis liquid chromatography tandem mass spectrometry approach alone or in combination with low-abundant protein enrichment technology (combinatorial peptide ligand library). In total, 1,822 proteins were quantified, 17.95% of them being detected only in plasma post enrichment. Across all life stages, the most abundant proteins were ankyrin-2, DNA primase large subunit, actin, serum albumin, apolipoproteins, hemoglobin subunits, hemopexin-like proteins and complement C3. When comparing the different life stages, 17 proteins involved in mechanisms to cope with hyperosmotic stress and retinal changes, as well as the downregulation of nonessential processes in smolts, were significantly different between parr and smolt samples. On the other hand, 11 proteins related to increased growth in post-smolts, and also related to coping with hyperosmotic stress and to retinal changes, were significantly different between smolt and post-smolt samples. Overall, this study presents a series of proteins with the potential to complement current seawater-readiness assessment tests in rainbow trout, which can be measured non-lethally in an easily accessible biofluid. Furthermore, this study represents a first in-depth characterisation of the rainbow trout blood plasma proteome, having considered three life stages of the fish and used both fractionation alone or in combination with enrichment methods to increase protein detection.

Decapod crustaceans, such as those from the Homarus genus, are key benthic representatives that support very valuable fishing and aquaculture industries. Those commercially caught, such as the European lobster (H. gammarus) can be stored in live facilities for short (a few days) to long periods (up to 6 months) before being traded. Conditions in captivity are not standardized, including holding temperatures or feeding regimes. Herein, the physiological condition during long-term starvation (24 weeks) in H. gammarus was assessed at three temperatures (4, 8, and 12^∘C). Our results indicate that, H. gammarus have the capacity to endure long-term starvation. Principal component analysis (PCA) of measured parameters showed two main components (Eigen value >1). Fasted animals kept at 12^∘C, separated from all other experimental groups due to higher total phenoloxidase (PO) activity in the hemolymph and water content in the muscle, suggesting that keeping H. gammarus un-fed at this higher temperature is physiologically more demanding and detrimental. This was later confirmed by significant changes, particularly in this group, in the histology and lipid class composition of the hepatopancreas. These data call into question the suitability of current accepted in vivo condition markers (e.g., hemolymph protein concentration) to determine the physiological condition and welfare of decapods such as H. gammarus.