Journal of fish biology最新文献

The Atlantic wolffish (Anarhichas lupus) is a cold-water fish with potential for aquaculture diversification. To unveil the mechanisms underlying the compromised growth in Atlantic wolffish when reared at higher temperatures, we investigated the relationship between temperature, growth rate, aerobic capacity, stress biomarkers, and gut barrier function. Juveniles acclimated to 10°C were maintained at 10°C (control) or exposed to 15°C for either 24 h (acute exposure) or 50 days (chronic exposure). Fish exposed to 15°C exhibited reduced growth, higher standard, and maximum metabolic rates compared to those at 10°C. In the chronically exposed group at 15°C, metabolic rates were lower than those of acutely exposed fish. The absolute aerobic scope exhibited no significant variation in temperatures; however, the factorial scope showed a notable reduction at 15°C in both acute and chronic exposed groups, aligning with a correlated decrease in individual growth rates. Chronic warming led to increased plasma glucose levels, indicating energy mobilization, but cortisol levels were unaffected. Furthermore, chronic warming resulted in reduced intestinal barrier function, as evidenced by increased ion permeability and a negative potential in the serosa layer. We conclude that warming elevates metabolic rates while reducing intestinal barrier function, thus increasing energy expenditure, collectively, limiting energy available for growth at this temperature from increased allostatic load. Thus, juvenile wolffish maintaining their aerobic scope under thermal stress experience slower growth. This research provides insights for improving the welfare and resilience of wolffish in aquaculture at elevated temperatures and understanding their response to increased environmental temperatures.

Assessing the nutritional status and identifying major causes of mortality in larvae experiencing varying degrees of starvation are crucial for establishing appropriate feeding protocols and enhancing the welfare of hatchery-reared fish. The black rockfish Sebastes schlegelii is an important species in aquaculture and stock enhancement efforts in China, Japan, and Korea. This study aimed to identify optimal diagnostic morphometric indicators of starvation in newly hatched (0-6 days post-hatch, DPH) and postlarval stages (27-37 DPH) of this valuable fish species through histological analyses. Our findings revealed that certain morphometric parameters, including body length, the ratios of eye diameter to head height, body height to body length, and abdomen height to body height, exhibit sensitivity to starvation during both larval and postlarval stages. Particularly, the ratios of body height to body length and abdomen height to body height emerged as the most sensitive morphometric indicators of starvation. Histological examinations of the digestive system revealed rapid alterations in the morphology of hepatic parenchymal cells, accompanied by a significant decrease in the number of lipid cells in the liver during episodes of food deprivation. Starvation induced cellular degeneration in the digestive organs, manifested by reduced heights of epithelial cells and mucosal layers in the intestine, oesophagus, and stomach, along with degeneration and separation of muscle fibers. Among these variables, the height of the intestinal submucosa and muscle layer emerged as the most sensitive indicators reflecting nutritional conditions in newly hatched larvae. In contrast, the height of intestinal striated borders and mucosal folds proved to be the most sensitive indicators in the postlarval stage. Furthermore, the height of intestinal epithelial cells and the number of lipid vacuoles in enterocytes exhibited high sensitivity to food deprivation in both newly hatched larvae and postlarvae. These findings underscore the varying resilience of fish to starvation during different developmental phases and highlight the utility of morphological sensitivity characteristics as reliable diagnostic indices for assessing nutritional status in relation to starvation or suboptimal feeding during the early developmental stages of black rockfish in hatchery-reared processes.

Haemoglobin concentration ([Hb]) assessment in fish blood has become a routine parameter to measure the health and welfare status of the animals. The original method (haemoglobincyanide method, best known as the Drabkin method) for measuring Hb in human and animals is not well suited for work outside of a laboratory setting. It is relatively time consuming, contains hazardous cyanide elements, and requires specific laboratory material. As an alternative to the Drabkin method, portable analysers have been developed for human blood, but they need to be first validated for fish blood before being used in experiments. In this study, the performance of the new HemoCue Hb 801 portable haemoglobin analyser was compared to the validated Drabkin method to determine [Hb] in three fish species. Hb readings between the two methods were not different for any of the species tested (rainbow trout, Onchorynchus mykiss, Atlantic wolffish, Anarhichas lupus, and Nile tilapia, Oreochromis niloticus). Therefore, this new portable device can be readily used to measure Hb in fish blood. Unlike the previous model from HemoCue, the Hb 201+, this device does not need an incubation time or a correction factor, representing a major gain of time and precision.

Various cleaner fish species, such as the lumpfish (Cyclopterus lumpus L.), are used in the sea cage production of Atlantic salmon (Salmo salar L.) as a control measure against the ectoparasitic salmon louse (Lepeophtheirus salmonis). Nonetheless, during severe lice infestation, alternative treatments are required to control parasitic burden. The aim of this study was to gain insight into how lumpfish skin responds to different chemicals used to treat parasites. The authors collected skin from lumpfish from both research facilities (tank-reared fish) and commercial production (cage-reared fish) and used operational welfare indicators, in vitro models, histology and transcriptomics to study how the skin responded to two anti-parasitic oxidative chemicals, hydrogen peroxide (H₂O₂) and peracetic acid. Lumpfish sampled from the farm were classified as clinically healthy or weak based on their morbidity status, and fish from each category were used to gain insight into how the therapeutics affect the skin barrier. Differences between healthy and weakened (moribund) fish, and between treated fish from each of the two groups, were observed. Histological examination showed an overall reduced skin quality in fish characterized as moribund, including different grades of exposed bony plates. In vitro oxidant-treated lumpfish skin had reduced the migration capacity of keratocytes, a weakened epidermal barrier, and altered gene transcription, changes that are known predisposing factors to secondary infections. Skin from non-treated, healthy fish sampled from commercial farms exhibited similar features and attributes to oxidant-exposed tank-reared fish from a research facility, suggesting that apparently healthy cage-held lumpfish exhibited stress responses in the epidermal barrier. The results of the study outline the risks and consequences lumpfish can face if accidentally subjected to potential anti-parasitic oxidant treatments aimed at Atlantic salmon. It also strengthens the evidence behind the requirement that lumpfish should be removed from the cages before being potentially exposed to this type of treatment and outlines the potential risks of differing husbandry practices upon lumpfish health, welfare and resilience.

Sea lice represent a persistent and growing problem, challenging the resilience and growth of the salmon aquaculture industry. In this Norwegian case study, we studied and discuss how the absence of policy instruments directed at stimulating breeding for lice resistance (LR) might be explained. We found well-documented opportunities for selection progress for LR. Hence, breeding on LR appears with an untapped potential. We discuss how market-based, legal, institutional and interest-based factors can explain the absence of policy instruments stimulating LR breeding. Methodologically, we obtained data from document and literature studies and interviews with key players (salmon breeders, farmers, nongovernmental organizations (NGOs) and governmental bodies in Norway). First, LR is a polygenic trait, which makes it poorly suited for patenting. Furthermore, if only a small proportion of fish farmers choose seeds with higher LR, other operators can easily take on the free-rider role because they will not suffer from reduced gain in growth performance as a result of a much stronger emphasis on LR in the breeding goal. The market is thus not expected to stimulate stronger selection for LR in Norwegian salmon breeding. Second, neither genetic engineering (e.g., gene editing), still struggling with consumer acceptance, nor the uncertainty associated with possible changes in the Norwegian Gene Technology Act stimulate investment in LR via, for example, CRISPR technology. Thirdly, public policy instruments in their entirety have targeted other types of innovations against salmon lice, and none have so far been used to stimulate breeding companies to emphasize LR more strongly in their breeding programmes. From a political point of view, it seems that breeding has been left to the market and the private sector. However, neither the NGOs nor the public seem to be aware of, or pay significant attention to, the breeding potential to improve LR and fish welfare. Fragmented management of the aquaculture sector can camouflage the close ties between political and business interests. The industry is hesitant to invest significantly in long-term breeding targets such as significantly higher genetic LR. This may strengthen the assumption that strong economic interests will reduce the role of science in knowledge-based management. As farmed salmon are increasingly being exposed to stressful delousing treatments, mortality and associated welfare problems have increased significantly. For instance, large fish die more often from cardiomyopathy syndrome (CMS), resulting in growing demand for CMS-resistant salmon. This gives rise to a paradoxical situation: increasing treatments with high mortality and fish welfare issues in farmed salmon, while the lice threat to wild salmon persists.

Optimal holding conditions are key to animal welfare. How stressful husbandry is perceived by the animal can be determined via an assessment of an animal's mental state - where it is positioned on the continuum between optimistic and pessimistic states - and can be measured using the judgement bias paradigm. In this test, individuals are trained to distinguish a rewarded from an unrewarded cue before being presented an ambiguous, intermediate cue. The response time to the ambiguous cue is then indicative of mental state. A shorter latency suggests a more positive (optimistic) mental state and a longer latency a more negative (pessimistic) mental state. Here, the authors used the judgement bias paradigm to assess the impact of standard laboratory housing conditions on the mental states of female guppies (Poecilia reticulata). As it is debated which holding conditions confer optimal welfare, they tested the impact of husbandry on mental state by keeping animals for 3 weeks in small or large social groups in either small or large tanks. They found that the different standard housing conditions used did not lead to differences in mental state. As an unexpected side result, they found that female guppies seem lateral. Their findings of comparable mental state across housing conditions suggest either that guppies perceive the tested conditions as equally stressful or, alternatively, that guppies are relatively resilient to the combination of group and tank sizes tested in this study. The authors conclude that the judgement bias paradigm can be a useful tool to assess fish welfare.

The objective of the present study was to investigate the optimal dietary protein requirement and the effect of varying protein levels on the growth and health of juvenile, wild-caught Atlantic wolffish, Anarhichas lupus, a promising candidate for cold-water aquaculture diversification. Six iso-energetic (ca. 18.3 MJ kg^-1), fish meal-based experimental diets were formulated with crude protein levels ranging from 35% to 60%, with graded increments of 5% in a 12-week feeding trial in a recirculating aquaculture system (RAS). Weight gain, specific growth rate (SGR), and condition factor (K) were evaluated in response to dietary protein levels. Liver, muscle, and blood parameters were assessed for possible changes in protein and lipid metabolism and welfare. Overall growth was highly variable throughout the experiment on all diets, as expected for a wild population. The feed with highest in protein (60%) inclusion resulted in the highest growth rates, with an average weight gain of 37.4% ± 33.8% and an SGR of 0.31% ± 0.2% day^-1. This was closely followed by feeds with 55% and 50% protein inclusion with an average weight gain of 22.9% ± 34.8% and 28.5% ± 38.3%, respectively, and an SGR of 0.18% ± 0.3% day^-1 and 0.22% ± 0.3% day^-1, respectively. Fish fed the high protein diets generally had increased hepatic lipid deposition (17%-18%) and reduced free fatty acid levels (3.1-6.8 μmol L^-1) in the plasma relative to fish that were fed the lower protein diets (35%-45%). No effects of diet were found on plasma protein levels or muscle protein content. Furthermore, stress parameters such as plasma cortisol and glucose levels were unaffected by diet, as were plasma ghrelin levels. Overall, these results suggest that a high protein inclusion in the diet for Atlantic wolffish is required to sustain growth with a minimum protein level of 50%.

Fish resilience can be understood as the capacity of fish to successfully respond to a challenge so that they are able to function and flourish in much the same way as they did prior to the occurrence of the challenge. Resilience is a function not only of individual fish, but also of a whole fish population. Enhancing the resilience of fish requires both adapting the robustness of the animals and adapting the (production) environment to the specific needs of the fish. Rather than a mere biological capacity of fish, resilience also comes with ethical questions. These questions occur at four levels. First, in practice resilience often comes with a "rhetoric" of optimalization. The view that aquaculture that strives for resilient fish is good for both fish welfare and production is inherently normative. It assumes a 'win-win situation', but thereby makes certain normative assumptions. Second, especially when the win-win situation is not achievable, resilience means making trade-offs between preferred responses to challenges from the perspective of individual animals and groups or between individual housing and larger aquaculture systems. Third, the discussions on resilience and fish demonstrate the need to move beyond an animal welfare framework when discussing the treatment of fish in aquaculture. Recently, animal ethics has seen a turn towards centering animals' own agency. This means that we should not only focus on improving animal welfare, but also on asking what the animals themselves want and how they can be given more control over their situation. This may also impact the definition of resilience and how it is made operational. Finally, the use of the concept of resilience may reveal a certain moral outlook with regard to fish. On the one hand, resilience is portrayed as a positive characteristic of animals that enables improvement of the quality of life of fish. At the same time, it raises the question of how far we should stretch the "manufacturability" of fish. When we physically adapt animals so that they can cope with difficult circumstances we may be stretching moral boundaries. For example, this raises the objection that we are instrumentalizing animals. In this article, we reflect on these types of ethical issues and aim to show that the ethical dimensions of resilience need to be taken into account by professionals in aquaculture in order to make resilience operational and to contribute to a responsible interaction with fish in aquaculture.

Due to the growth of aquaculture and the finite supply of fishmeal and oil, alternative marine protein and lipid sources are highly sought after. Particularly promising is the use of side streams from the fish processing industry, allowing for the recovery and retention of otherwise lost nutrients in the food production chain. The aim of the present study was to evaluate the potential of three fish processing side streams as fish feed ingredients. The side streams originated from different stages of the production chain, were used without further processing, and included sprat trimmings (heads, frames, viscera), marinated herring (fillets), and mackerel in tomato sauce (fillets and sauce). The three side streams contained moderate levels of protein (28-32% dry matter) and high levels of lipid (34-43%). The sprat trimmings included ca. 29% ash and 1.5% phosphorous, which may add value due to the high level of essential minerals but needs to be considered in feed formulations. Three diets were formulated to include 50% of each side stream replacing all fishmeal and ca. 80% of the fish oil of the control diet, which contained 35% fishmeal and 10% fish oil. The diets were evaluated in a 12-week feeding trial using rainbow trout (Oncorhynchus mykiss). Fish fed the sprat diet displayed the highest feed intake and growth and showed no negative effects on the intestinal health. The mackerel side stream displayed a good digestibility but resulted in lower growth rates compared to the sprat trimmings. Fish fed the herring diet displayed the lowest performance regarding growth, feed intake, and digestibility. They further exhibited a reduction in nutrient uptake in both proximal and distal intestines, likely contributing to the observed lower digestibility and growth, and a reduction in plasma ghrelin levels. As part of a circular approach to increase marine lipid and protein production for fish feed, the tested sprat and mackerel side streams are promising raw materials; however, additional studies using more commercial-like feed formulations are encouraged.