Bio-sensing technologies in aquaculture: how remote monitoring can bring us closer to our farm animals.

Farmed aquatic animals represent an increasingly important source of food for a growing human population. However, the aquaculture industry faces several challenges with regard to producing a profitable, ethical and environmentally sustainable product, which are exacerbated by the ongoing intensification of operations and increasingly extreme and unpredictable climate conditions. Fortunately, bio-sensors capable of measuring a range of environmental, behavioural and physiological variables (e.g. temperature, dissolved gases, depth, acceleration, ventilation, heart rate, blood flow, glucose and l-lactic acid) represent exciting and innovative tools for assessing the health and welfare of farmed animals in aquaculture. Here, we illustrate how these state-of-the-art technologies can provide unique insights into variables pertaining to the inner workings of the animal to elucidate animal-environment interactions throughout the production cycle, as well as to provide insights on how farmed animals perceive and respond to environmental and anthropogenic perturbations. Using examples based on current challenges (i.e. sub-optimal feeding strategies, sub-optimal animal welfare and environmental changes), we discuss how bio-sensors can contribute towards optimizing the growth, health and welfare of farmed animals under dynamically changing on-farm conditions. While bio-sensors currently represent tools that are primarily used for research, the continuing development and refinement of these technologies may eventually allow farmers to use real-time environmental and physiological data from their stock as 'early warning systems' and/or for refining day-to-day operations to ethically and sustainably optimize production. This article is part of the theme issue 'Measuring physiology in free-living animals (Part I)'.

Stunning fish with CO2 or electricity: contradictory results on behavioural and physiological stress responses.

Studies that address fish welfare before slaughter have concluded that many of the traditional systems used to stun fish including CO2 narcosis are unacceptable as they cause avoidable stress before death. One system recommended as a better alternative is electrical stunning, however, the welfare aspects of this method are not yet fully understood. To assess welfare in aquaculture both behavioural and physiological measurements have been used, but few studies have examined the relationship between these variables. In an on-site study aversive behaviours and several physiological stress indicators, including plasma levels of cortisol and ions as well as blood physiological variables, were compared in Arctic char (Salvelinus alpinus) stunned with CO2 or electricity. Exposure to water saturated with CO2 triggered aversive struggling and escape responses for several minutes before immobilization, whereas in fish exposed to an electric current immobilization was close to instant. On average, it took 5 min for the fish to recover from electrical stunning, whereas fish stunned with CO2 did not recover. Despite this, the electrically stunned fish had more than double the plasma levels of cortisol compared with fish stunned with CO2. This result is surprising considering that the behavioural reactions were much more pronounced following CO2 exposure. These contradictory results are discussed with regard to animal welfare and stress physiological responses. The present results emphasise the importance of using an integrative and interdisciplinary approach and to include both behavioural and physiological stress indicators in order to make accurate welfare assessments of fish in aquaculture.

Behavioural fever boosts the inflammatory response in rainbow trout Oncorhynchus mykiss.

Behavioural fever, manifested as an increased preferred temperature, was shown in rainbow trout Oncorhynchus mykiss following an injection of bacterial lipopolysaccharide. Simulated behavioural fever, through a 2·5° C water temperature rise following bacterial lipopolysaccharide injection, enhanced the expression of the cytokine interleukin-1ß, in comparison with an untreated group held at the initial temperature. The present findings show that an important mediator in the immune response can be boosted through behavioural fever in fishes.

Recovery of gastric evacuation rate in Atlantic cod Gadus morhua L surgically implanted with a dummy telemetry device.

The current study investigated how the gastric evacuation rate (GER) was affected after surgically introducing dummies of a blood flow biotelemetry system into the abdominal cavity of Atlantic cod, Gadus morhua. Gastric evacuation experiments were performed two and 10 days postsurgery on surgically implanted and control G. morhua force-fed sandeel, Ammodytes tobianus. The results were compared with previously obtained estimates from unstressed conspecifics voluntarily feeding on a similar diet. After two days, GER was significantly lower in the group of fish with the dummy implants compared with the control group, but following 10 days of recovery no significant difference was seen between the two groups. The difference between implanted and control fish observed two days postsurgery may have resulted either from surgery, postsurgical stress and/or the presence of the implant. The conclusion is that 10 days of postsurgical recovery will stabilize GER in G. morhua, thus indicating that at this point the implant per se did not affect GER. Both the fish with surgical implants and controls in this study evacuated their stomachs much slower and with much higher interindividual variation compared with G. morhua feeding voluntarily on similar prey items. The lower GER and higher interindividual variation for force-fed fish indicate that handling, anaesthetization and force-feeding impair GER and that individual fish respond differently to the suppressing effects.

Effects of feeding on thermoregulatory behaviours and gut blood flow in white sturgeon (Acipenser transmontanus) using biotelemetry in combination with standard techniques.

The effects of thermoregulatory behaviours on gut blood flow in white sturgeon Acipenser transmontanus before and after feeding was studied using a blood flow biotelemetry system in combination with a temperature preference chamber. This is the first study to look at cardiovascular responses to feeding in white sturgeon, and also the first time behavioural tests in fish have been combined with recordings of cardiac output, heart rate, cardiac stroke volume and gut blood flow. The results showed strong correlations between gut blood flow and temperature choice after feeding (R(2)=0.88+/-0.03, 6-8 h postprandially and R(2)=0.89+/-0.04, 8-10 h postprandially) but not prior to feeding (R(2)=0.11+/-0.05). Feeding did not affect the actual temperature preference (18.4+/-0.7 degrees C before feeding, 18.1+/-0.7 degrees C, 6-8 h postprandially and 17.5+/-0.5 degrees C, 8-10 h postprandially). Fish instrumented with a blood flow biotelemetry device, and allowed to move freely in the water, had a significantly lower resting heart rate (37.3+/-0.26 beats min(-1)) compared with the control group that was traditionally instrumented with transit-time blood flow probes and kept in a confined area in accordance with the standard procedure (43.2+/-2.1 beats min(-1)). This study shows, for the first time in fish, the correlation between body temperature and gut blood flow during behavioural thermoregulation.