UixKlow

10/01/2022

We solved the mystery of why some fish are warm-blooded
For over 50 years now, scientists have known that, despite their reputation, not all fish are cold-blooded. Some shark and tuna species, the white shark and the Atlantic bluefin tuna, have evolved the ability to warm parts of their bodies, such as their muscle, eyes and brain.

About 35 species of fishes – accounting for less than 0.1% of all described fishes – have this ability, which allows them to stay warmer than the water around them. Until recently, however, the reason this ability evolved was a mystery.

Some scientists believed being warm-blooded allowed the fish to swim faster, as warmer muscles tend to be more powerful. Others thought it allowed them to live in a broader range of temperatures, making them less susceptible to the effects of ocean warming caused by climate change. With this in mind, an international team of marine biologists and I set out to answer the puzzle of why some fish warm-blooded when most aren’t.

Our study found fishes’ ability to warm their bodies provides competitive advantages – they can swim faster than their cold-blooded relatives. However, this doesn’t necessarily mean they’ll be able to adapt to changing ocean temperatures under climate change better than cold-blooded fish, according to our results.

Catching fish
Our team – from Australia, USA, Tasmania, Hawaii and Japan – collected data from wild sharks and bony fish, as well as using data which had already been collected. We attached biologging devices – waterproof, electronic devices that can remotely record data – to the fins of the animals we caught. Animals were caught by hook and line and secured alongside a boat. This allowed us to the attach the devices and release the animals immediately after.

These devices gathered information such as water temperatures encountered by the fish in their habitats, the speeds at which the fish swam for most of the day and the depths of water the fish swam in.

By comparing the speed and temperature data of these warm-blooded and cold-blooded animals we could calculate the range of temperature these animals were swimming in and what speeds they were swimming at, accounting for their body weights. It turns out that warm-blooded fish can swim 1.6 times faster than cold-blooded fish. This is some of the first direct evidence of the evolutionary advantage of being warm-blooded.

This extra speed provides advantages when it comes to things like predation and migration. It’s likely that this makes them better hunters or travellers. The faster swim speeds also aid the fish in identifying prey. The quicker they swim, the faster an image moves across their eye, allowing them to process and identify the image – perhaps of prey – faster than slower counterparts.

A white shark under the water, face on.
We collected data from sharks and tuna. Andrew Fox, Author provided (no reuse)
It has previously been suggested that these warm-blooded fishes may be better able to deal with changing ambient temperatures by stabilising their body temperatures. This would be useful under current climate change scenarios, such as global ocean warming.

That may be the case, but our results indicate the ability to warm their bodies doesn’t allow them to occupy a broader temperature or depth ranges. This means we may have been overstating the resilience warm-blooded fish have for facing changing ocean temperatures.

Many of these animals are already facing threats from ocean warming, and human-induced risks. The Atlantic bluefin tuna is an endangered species while the white shark is classed as vulnerable. We hope that taking these findings into account could better inform future work on the conservation and protection of these unique but threatened animals.

10/01/2022

Fish hooked on m**h – the consequences of freshwater pollution
Around 269 million people worldwide use drugs each year. Often forgotten in this story is a problem of basic biology. What goes in must come out. Sewers are inundated with drugs that are excreted from the body, along with the broken down chemical components that have similar effects to the drugs themselves.

Sewage treatment plants don’t filter these things out – they were never designed for it. A lot of sewage also finds its way into rivers and coastal waters untreated. Once in the environment, drugs and their byproducts can affect wildlife. In a recent study published in the Journal of Experimental Biology, researchers in the Czech Republic investigated how m**hamphetamine – a stimulant with a growing number of users worldwide – might be affecting wild brown trout.

They examined whether concentrations of m**hamphetamine and one of its byproducts, amphetamine, which were estimated from other studies that have measured illicit drug concentrations in waterways, could be detected in the brains of brown trout. They also looked at whether these concentrations were enough to cause the animals to become addicted.

White m**hamphetamine crystals on a black background with a glass m**h pipe.
Recreational m**hamphetamine users often smoke crystal m**h. AMF Photography/Shutterstock
The trout were exposed to the drug in large tanks over eight weeks and then put into withdrawal, going “cold turkey” in drug-free tanks for ten days. During that time, the researchers tested the fish’s preference for fresh water or water containing m**hamphetamine and compared this with the responses of fish that had never been exposed to the drug.

Their findings were intriguing. The m**hamphetamine-exposed fish preferred the water containing the drug, while no such preference was shown for the untreated fish. The researchers also found that during their withdrawal period, the m**hamphetamine-exposed trout moved less. The researchers interpreted this as a sign of anxiety or stress – typical signs of drug withdrawal in humans.

The brain chemistry of the exposed fish differed from the unexposed, too, with several detected changes in brain chemicals that correspond to what is seen in cases of human addiction. Even after the behavioural effects had waned after ten days of withdrawal, these markers in the brain were still present. This suggests that m**hamphetamine exposure could have long-lasting effects, similar to what is seen in people.

How drugs affect ecosystems and fish biology
Why should we care if trout are becoming addicted to drugs? There are several reasons.

If the trout are “enjoying” the drugs, as they appear to be in the recent study, they may be inclined to hang around pipes where effluent is discharged. We know that fish can behave similarly to what is seen in humans suffering from addiction, not only from this trial, but from several studies on different fish species. One of the hallmarks of drug addiction is a loss of interest in other activities – even those that are usually highly motivated, such as eating or reproducing. It’s possible that the fish might start to change their natural behaviour, causing problems with their feeding, breeding and, ultimately, their survival. They may, for instance, be less likely to evade predators.

Exposure to drugs not only affects the fish themselves, but their offspring. In fish, addiction can be inherited over several generations. This could have long-lasting implications for ecosystems, even if the problem was fixed now.

This is not the first study to find illicit drugs in wildlife. In 2019, scientists in the UK reported co***ne in freshwater shrimp in all 15 rivers they sampled. Interestingly, they detected illicit drugs more often than some common pharmaceuticals.

But the wider effects of those drugs remain largely unknown. There have, however, been comprehensive studies into the effects of pharmaceuticals in rivers.

Read more: Five ways fish are more like humans than you realise

Pharmaceutical pollution
Medicines do not fully break down in our bodies either and arrive at wastewater treatment plants in faeces and urine. Most are discharged with wastewater effluent, but some enter rivers by seeping from landfills or farm fields where human sewage is used as fertiliser. Wildlife living in rivers and coastal waters where effluent is discharged are exposed to cocktails of medicines, from painkillers to antidepressants.

Caged fish downstream of some water treatment plants changed s*x from male to female within a few weeks due to exposure to hormone-disrupting chemicals found in contraceptive pills. Recent studies have shown that antidepressants can cause a wide range of behavioural changes in aquatic organisms from aggression, attraction to light and increasing boldness.

Drug addiction is a global health concern that can devastate communities, and tackling its environmental consequences will be expensive. One study has estimated it would cost over US$50 billion (£36 billion) to upgrade wastewater treatment plants in England and Wales so that they can remove these chemicals.

Water flowing out of a concrete grate into a river.
Drugs can’t be filtered from sewage without significant upgrades to existing infrastructure. Marekuliasz/Shutterstock
It might seem obvious that prescribed and illegal drugs designed to change behaviour in humans also change the behaviour of wildlife. But this problem is potentially far more widespread and complex. We don’t even know if synthetic chemicals in everyday household products, such as cosmetics, clothes and cleaning agents, can affect the behaviour of people and other species. An international group of scientists has urged companies and regulating bodies to check their toxic effect on behaviour as part of risk assessments of new chemicals.

We must get to grips with the amount of pharmaceuticals in our waterways. The world is some way from fixing the problems of addiction and illicit drug use. But, at the very least, more should be done to improve filtration in sewage treatment plants, and to force water companies to take more responsibility for ensuring effluent doesn’t affect wildlife.

10/01/2022

A test to diagnose psychopaths can help identify fish behaviours that could benefit aquaculture
In November 1888, fear stalked the streets of London as the Whitechapel Murderer claimed his latest victim. The unusually gruesome attacks had puzzled investigators, so police surgeon Dr. Thomas Bond examined the victims for clues that might help reveal the killer’s identity. Dr. Bond concluded that the violence of these attacks meant that the Whitechapel Murderer — who would later become known as Jack the Ripper — was a reclusive man with a strong impulsive drive.

Dr. Bond had created the first offender profile, applying a psychological technique that assumes an individual’s behaviour is consistent over time and that similar crimes are committed by similar offenders. These assumptions are controversial among psychologists, although police investigators have since used this approach to create criminal profiles that narrow suspect lists for unsolved cases.

Perhaps the most famous profiling tool is the Hare Psychopathy Checklist. This test scores responses to a series of questions to build a personality profile, which is then used to predict the likelihood of a person showing psychopathic behaviour.

Profiling personalities
Personality profiling is not unique to criminology. The m**hod is used to identify health risks, aid personnel recruitment, develop education programs and build dating apps. Despite this wide range of applications, there is one thing all these approaches have in common: they are almost exclusively used on humans.

Biologists recognize that animals have personality traits that are consistent across time. However, animal behaviour is often studied in large groups of animals so that data can be collected to investigate wide-scale trends. This means the need to build detailed personality profiles on an individual scale is uncommon.

Unless, as demonstrated by the case of Jack the Ripper, there are unknown individuals within a population that exhibit a rare behaviour and are avoiding detection.

Underwater mystery
Cleaner fish remove and eat parasites from the skin of other fishes. Some species of cleaner fish are used in salmon aquaculture to help control parasitic sea lice. Lumpfish are a commonly used cleaner fish, and millions of juveniles are released into salmon farms each year. However, only a minority of lumpfish (around 20 per cent) actually clean salmon of sea lice, while the rest either ignore salmon or compete for pellet food.

It is unclear why only certain lumpfish clean salmon and observing this behaviour is exceedingly rare. As part of a research team at the Centre for Sustainable Aquatic Research at Swansea University, my colleagues and I tried to solve this mystery by following the same logic as the Hare Psychopathy Checklist.

A lumpfish near a measuring ruler
Applying a personality profiling approach to lumpfish — and potentially other animals — can reveal useful information about their behaviour. (AUTHOR), Author provided
We designed a series of behavioural tests to build detailed personality profiles of lumpfish, in hope of identifying the individuals that showed cleaning behaviour. This involved testing for variation in activity, aggression, anxiety, boldness and sociality of individual lumpfish over repeated sessions, and then recording how these individuals interacted with salmon.

Friend or foe?
We found that most lumpfish completely ignored salmon and had very few interactions. However, lumpfish with “bold and non-aggressive” personality profiles spent long periods visually inspecting salmon in a co-operative manner. This would give these individuals opportunity to clean sea lice from salmon and help reduce parasite numbers in farms.

Profiling analysis revealed an unexpected second group of lumpfish with “active and social” personality profiles. These individuals caused salmon to flee, which suggests confrontation between the fish that would not be beneficial for cleaning in farms.

Our results showed that personality influences behavioural interaction between lumpfish and salmon. While some lumpfish are well suited for cleaning parasites, other individuals hinder cleaning and should not be used in aquaculture.

two lumpfish in a tank
Lumpfish are raised in hatcheries to supply salmon farms. (Emily Costello), Author provided
Future animal profiling
Profiling can be used to predict which individuals are likely to show cleaning behaviour. Not only will this increase the efficiency of cleaner fish for controlling sea lice in farms, it will also help improve fish welfare by removing lumpfish not suited for a farm environment.

Ongoing research collaborations between the University of Guelph and Fisheries and Oceans Canada aim to adapt this new approach so that it can be applied on a commercial scale.

Read more: Salmon farms are in crisis – here's how scientists are trying to save them

Despite its sinister beginnings, personality profiling has proven effective at predicting the behaviour of humans, and now lumpfish. This approach could provide new ways for studying animal behaviour by giving detailed insight on an individual scale.

10/01/2022

10/01/2022