zoo:logic

Amazing new research has shown that we can detect what species of fish are found in different parts of our seas simply by collecting samples of the local seawater. The key to identifying which species are present is in traces of DNA - known as environmental DNA (eDNA) - which are left in the surrounding water by fish that pass through. Just half a litre of seawater from a temperate marine ecosystem in Denmark provided DNA fragments from 15 different fish species, including some that were rarely recorded by more invasive conventional methods, as well as 4 bird species. Experiments show that even small fragments of eDNA degrade to the point that they are no longer detectable within days, suggesting that the method gives an up-to-date and accurate recording of the species that inhabit the area at that point in time. A further study looking into the possibility of marine mammal detection using the eDNA method suggests that greater volumes of seawater are needed to be analysed in order to detect them, but that eDNA has the potential to support current visual and acoustic methods of species detection for marine mammals as well as fish.

Ref: Thomsen P. F. et al., 2012. Detection of a diverse marine fish fauna using environmental DNA from seawater samples. PLOS One [link]
Foote A. D. et al., 2012. Investigating the potential use of environmental DNA (eDNA) for genetic monitoring of marine mammals. PLOS One [link] 

New research has shown that Atlantic salmon (Salmo salar) experience a feeling akin to frustration when they are not given a reward they are expecting to receive - a response previously only observed in mammals and birds. Debates over the ethics of fishing often throw up questions of whether fish are ‘conscious’ and have an awareness of pain, which has fuelled a fair amount of research in the area. Fish have been shown to be capable of responding to classical conditioning and to have long-term memories; however, we are still unsure to what extent their cognitive abilities are linked to conscious moods and emotions. This concept was studied in the salmon using a model commonly used in mammalian research called omission of expected reward (OER). In these experiments, animals are conditioned to associate a certain stimulus with a positive reward, such as food, and are then subjected to the stimulus without receiving the reward to record how they react. In mammals, OER has consistently been shown to cause animals to become stressed and aggressive.

Six groups, each consisting of 200 fish, were conditioned to associate a flashing light with feeding over a period of 22 days. By the end of this period, the fish showed attraction to the light due to association with the food reward, as opposed to their initial reaction of avoiding it. Three of the groups were then subjected to OER for 9 days - the fish were fed three times a day, and at two of these mealtimes, the expected food reward was delayed by 30 minutes. The other three groups carried on as normal, acting as controls.

When the groups were compared, OER groups showed higher aggression and greater hierarchy, causing some individuals to grow more quickly at the expense of others - interestingly, even during the one meal a day when the reward was provided immediately, aggression levels remained high. Stress levels were measured by detecting the concentration of cortisol (a hormone which is involved in stress response) in the blood, but unlike the variation seen in aggressive behaviour, these were the same across all groups, suggesting that although there were behavioural signs of stress this did not translate to a physiological stress reaction.

There are two possible explanations for the variation in aggressive behaviour:
- Dominant individuals may be trying to keep their position for prime access to food in expectation of the coming reward
- Aggression triggered by the stressful situation may be being displaced towards other individuals to help in coping with the conditions.
In either case this leads to stronger hierarchy and more uneven distribution of resources, as was observed in this study. 

The overall conclusion is that fish respond behaviourally to frustrating conditions just like birds and mammals, suggesting this could be an adaptive response to unpredictable environments that has been conserved throughout vertebrate evolution. While we cannot yet conclude that fish definitely experience conscious emotional states, the results do highlight the importance of regular routine for domestic or farmed fish in order to reduce aggressive interactions between individuals that may be detrimental to the health of the population.

Ref: Vinas M. A. et al., 2012. Omission of expected reward agitates Atlantic salmon (Salmo salar). Animal Cognition  Online first [link]

Everyone’s favourite smiley-faced cetaceans are more than just… well, a smiley face. Recent research has investigated dolphins’ incredible ability to heal from traumatic wounds such as those from a shark bite - injuries that would be fatal in a human being - without bleeding to death, becoming infected, or even seeming to experience pain. Not only this, but in healing the wound dolphins manage to almost totally restore the body contour from what was a deep, gaping laceration. The review provides some insight into how this might occur. Dr Zasloff of Georgetown University Medical Centre suggests that blood loss may be controlled by the same mechanism that reduces blood flow to the periphery of the body during deep dives (the diving reflex); that natural compounds known as organohalogens in blubber prevent infection through antimicrobial and antibiotic activity; and that recovery from a wound is less like the process of healing in humans and more like regeneration, allowing almost complete rebuilding of the tissues into the body contour. Least understood is the apparent lack of pain. Further neurological and physiological research will be required to find out exactly how pain is reduced.

In addition, research has recently discovered that the Guiana dolphin (Sotalia guianensis) is the first true mammal to be found to be able to detect the electrical fields of their prey - the ability has previously only been seen in some fish, amphibians and primitive egg-laying mammals such as the duck-billed platypus. The electro-sensory organ in the dolphin is located in the upper jaw, and is evolutionarily derived from whiskers. Electro-sensory perception is much better at locating prey over short distances, for which echolocation is not so useful.

Ref: Mallet (2011) Dolphins’ remarkable recovery from injury offers important insights for human healing. EurekAlert! [link] || Hooper (2011) Electric dolphins: cetaceans with a seventh sense. New Scientist News [link]