Scientists from the U.S. Geological Survey (USGS) have revealed that largemouth bass injected with oestrogen produces less hepcidin than normally. Hepcidin is an important iron-regulating hormone in fish, amphibians and mammals, and researchers also suspect that hepcidin may act as an antimicrobial peptide. In vertebrate animals, antimicrobial peptides are the body’s first line of defence against unwelcome bacteria and some fungi and viruses, so if there’re right, a lowered amount of these compounds is certainly not good news.

“Our research suggests that estrogen-mimicking compounds may make fish more susceptible to disease by blocking production of hepcidin and other immune-related proteins that help protect fish against disease-causing bacteria,” says lead author Dr. Laura Robertson.

You can find more info in the study “Identification of centrarchid hepcidins and evidence that 17β-estradiol disrupts constitutive expression of hepcidin-1 and inducible expression of hepcidin-2 in largemouth bass (Micropterus salmoides)” by Laura Robertson, Luke Iwanowicz and Jamie Marie Marranca in the latest issue of the journal Fish & Shellfish Immunology. It is the first published study demonstrating control of hepcidin by estrogen in any animal.

As reported earlier, fish populations may adapt and change in response to significant fishing pressure. Researchers are now suggesting that the genetic make-up of cod in the Atlantic Ocean might be changing, since cods genetically predisposition to seek out shallower waters are more likely to end up in nets or on fishing lines, while deep-dwellers are more likely to survive and reproduce.

If the current over-fishing of shallow living cod is not put to an end, evolutionary biologist Einar Árnason and his colleagues believes the genetic variant found in shallow-living cod will be lost all together. If the deep-water cods do not spread into the shallows, and Árnason doubts they will since they are adapted to deep water conditions, the shallows may be become devoid of cod within the next 10 years. This will decrease the size of the total cod population and will also force the fishing industry to either give up cod fishing altogether or switch to expensive deep-water trawling.

Árnason and his colleagues have studied cod populations off the coast of Iceland, where fish stocks are still in fairly decent condition compared to the severely depleted populations found in the western Atlantic. In their study, the researchers examined how the genotypes of Icelandic cod have changed between 1994 and 2003.

It was already known that cod living in the Icelandic shallows have a different variant of the pantophysin I gene than the cods found at much larger depts. In their study, Árnason and his colleagues found that the shallow-water variant of pantophysin I is becoming increasingly rare; a change which they attribute to the fact that most Icelandic cod fishers work in shallow waters near the coastline using lines and nets instead of carrying out deep-water trawling.

Árnason and his team also found that Icelandic cod are reaching sexual maturity at a younger age and at a smaller size than before. This is discovery is a chilling revelation for Icelandic fishermen and conservationalists alike, since that was exactly what happened in Newfoundland waters before that cod population crashed completely.

The study has been published in the journal PLoS ONE

After acknowledging the failure of current fishery policies within the union, EU officials are now considering banning the practice of discarding fish at sea.

“What’s the point of setting a quota if fishermen aren’t accountable for the fish they actually catch?” says Mogens Schou, a Danish fishery official.

The EU’s quotas limit the size of the annual catch that countries and their fleets can sell on their return to harbour, but instead of protecting remaining fishing populations from depletion, the system is making fishermen dump lower-value fish at sea to maximize profit. According to officials in the European Commission’s fisheries office, most of these fishes do not survive.

“To stay under their quotas, and make more money, fishermen discard half of what they catch,” says Schou, “They ‘high-grade’ – in other words, only keep the most profitable fish.”

Last month, an EU report was released highlighting the failure of current EU fishing regulations by showing that 88% of fish species in EU waters are being fished out faster than they can reproduce. In response to the report, fishery ministers from the 27 EU nations are currently discussing how to protect the remaining fish stocks from complete eradication.

As a part of these talks, Denmark has proposed an amended quota system where fishermen and their countries are held accountable for the amount of fish caught rather than the amount returned to port. To make it harder for fishing fleets to cheat, Denmark is also proposing that fishermen voluntarily equip their boats with on-board cameras. In exchange, the fishermen would get bigger quotas.

Denmark has already designed a surveillance kit consisting of four cameras, a GPS (Global Positioning System) device, and sensors that notice when fish is being hauled or dumped. The Danish kits are currently being used on six fishing boats with Danish officials monitoring the footage.

Danish fisherman Per Nielsen installed the kit on his trawler Kingfisher in September and believes it to be a good investment. The kit cost roughly 10,000 USD, but Nielsen was compensated by being allowed to catch several extra tens of thousands of dollars worth of cod.

As of now, EU fishermen throw overboard an estimated 50% of the fish they catch and did for instance dump 38% of the 24,000 tons of cod they caught last year, according to the International Council for the Exploration of the Sea.

If you want to learn more about how the charismatic creatures known as stingrays feed, you should check out a new study published in the most recent issue of Neotropical Ichthyology.

While spending days and nights scuba diving and snorkelling in the upper Paraná River of Brazil, researchers Domingos Garrone-Neto and Ivan Sazima made 132 observations of freshwater stingrays and noticed three different forms of foraging behaviour.

Picture of Motoro Sting Ray, Ocellate river stingray – Potamotrygon motoro.
Copyright www.jjphoto.dk

The first hunting technique involved hovering close to the bottom, or even settle on top of it, while undulating the disc margins. By doing so, the stingray would stir up the substrate, unveiling small invertebrates. The invertebrates – typically snails, crabs and larval insects – could not escape from under the ray’s disc and ended up as food.

When using its second hunting technique, the stingray would slowly approach shallow water while keeping its eyes on suitable prey items that concentrate in such environments. When it got close enough, it would make a rapid attack; stunning the prey or trapping it under its disc. This hunting technique did not target tiny invertebrates hiding in the sand; it focused on tetras and freshwater shrimps instead. The studied stingrays only used this method during the night when they could sneak up on prey without being seen.

The third technique observed relied on the presence of vertical or inclined surfaces in the water, such as boulders and tree stumps, including man-made structures like concrete slabs. On this type of objects a lot of different organisms, e.g. snails, like to crawl around or attach themselves. The hunter would simply position itself with the anterior part of its disc above the water’s edge and start picking the animals off the surface, one at a time.

The two studied species were Potamotrygon falkneri and Potamotrygon motoro; both belonging to a genus of freshwater stingrays found exclusively in South America.

As mentioned above, you can find the paper in Neotropical Ichthyology 7.

Garrone-Neto, D and I Sazima (2009) Stirring, charging, and picking:

hunting tactics of potamotrygonid rays in the upper Paraná River. Neotropical Ichthyology 7, pp. 113–116.

The inclination to end up stuck on a hook seems to be a heritable trait in bass, according to a study published in a recent issue of the Transactions of the American Fisheries Society.

The study, which was carried out by researchers DP Philipp, SJ Cooke, JE Claussen, JB Koppelman, CD Suski, and DP Burkett, focused on Ridge Lake, an Illinois lake where catch-and-release fishing has been enforced and strictly regulated for decades. Each caught fish has been measured, tagged and then released back into the wild.

Picture by: Clinton & Charles Robertson from Del Rio, Texas & San Marcos, TX, USA

David Philipp and coauthors commenced their study in 1977, checking the prevalence of Largemouth bass (Micropterus salmoides) on the hooks of fishermen. After four years, the experimental lake was drained and 1,785 fish were collected. When checking the tags, Philipp and his team found that roughly 15 percent of the Largemouth bass population consisted of specimens that had never been caught. They also found out that certain other bass specimens had been caught over and over again.

To take the study one step further, the research team collected never caught bass specimens (so called Low Vulnerability, LV, specimens) and raised a line of LV offspring in separate brood ponds. Likewise, the team collected bass specimens caught at least four times (High Vulnerability, HV, specimens) and placed them in their own brooding ponds to create a HV line.

The first generation (F1) offspring from both lines where then marked and placed together in the same pond. During the summer season, anglers where allowed to visit the pond and practise catch-and-release, and records where kept of the number of times each fish was caught.

As the summer came to an end, HV fish caught three or more times where used to create a new line of HV offspring, while LV fish caught no more than once became the parents of a new LV line.

The second generation (F2) offspring went through the same procedure as their parents; they were market, released into the same pond, and subjected to anglers throughout the summer. In fall, scientists gathered the fish that had been caught at least three times or no more than once and placed them in separate ponds to create a third generation (F3) HV and LV fish.

A following series of controlled fishing experiments eventually showed that the vulnerability to angling of the HV line was greater than that of the LV line, and that the differences observed between the two lines increased across later generations.

If this is true not only for bass but for other fish species as well, heavy hook-and-line angling pressure in lakes and rivers may cause evolutionary changes in the fish populations found in such lakes. Hence, a lake visited by a lot of anglers each year may eventually develop fish populations highly suspicious of the fishermen’s lure.

More information can be found in the paper published in Transactions of the American Fisheries Society: Philipp, DP, SJ Cooke, JE Claussen, JB Koppelman, CD Suski and

DP Burkett (2009) Selection for vulnerability to angling in Largemouth Bass. Transactions of the American Fisheries Society 138, pp. 189–199.

A Hawaiian company wants to build the world’s first commercial Bigeye tuna farm, in hope of creating a sustainable alternative to wild-caught big eye.

Bigeye tuna, Thunnus obesus, is the second most coveted tuna after the famous Bluefin tuna and the wild populations have been seriously depleted by commercial fishing fleets. As Bluefin is becoming increasingly rare due to over-fishing, consumers are turning their eyes towards Thunnus obesus – which naturally puts even more stress on this species that before.

In 2007, fishermen caught nearly 225,000 tons of wild Bigeye in the Pacific. Juvenile bigeye tuna like to stay close to floating objects in the ocean, such as logs and buoys, which make them highly susceptible to purse seine fishing in conjunction with man-made FADs (Fish Aggregation Devices). The removal of juvenile specimens from the sea before they have a chance to reach sexual maturity and reproduce is seriously threatening the survival of this tuna species.

“All indications are we’re on a rapid race to deplete the ocean of our food resources,” said Bill Spencer, chief executive of Hawaii Oceanic Technology Inc. “It’s sort of obvious _ well, jeez we’ve got to do something about this.”

Techniques to spawn and raise tuna fry are still being tentatively explored by scientists in several different countries, including Australia and Japan. As of today, most tuna farms rely on fishermen catching juvenile fish for them, but Hawaii Oceanic Technology plans to artificially hatch Bigeye tuna at a University of Hawaii lab in Hilo.

Once the young tunas from the lab have grown large enough, they will be placed in the 12-pen tuna farm that Hawaii Oceanic is planning to build roughly 3 miles off Big Island’s west coast. Each pen will have a diameter of 50 metres (168 feet) and the entire farm will be spread out over one square kilometre (250 acres). If everything goes according to plan, this project will yield 6,000 tons of Bigeye per annum. The fish will not be harvested until it reaches a weight of at least 45 kg (100 lbs).

In an effort to avoid many of the common problems associated with large scale commerical fish farmning, Hawaii Oceanic Technology will place their pens at a depth of 1,300 feet (400 metres) where currents are strong. The company also plans to keep their pens lightly stocked, since dense living conditions are known to increase the risk of disease in fish farms.

Farming pens can cause problems for the environment if fish waste and left-over food is allowed to collect under the pens, suffocating marine life living beneath. Other problems associated with fish farming are the release of antibiotics into the water and the escape of invasive species.

Fish farms can also put pressure on fish further down in the food chain since vast amounts of food is necessary to feed densely packed fish pens, and Peter Bridson, aquaculture manager at the Monterey Bay Aquarium in California, is concerned about how much fish meal the Hawaiian farm will use need to feed its tuna.

“You kind of have to come back to the whole debate on whether these fish are the right thing for us humans to be eating,” said Bridson. “There are lots of other things which have a lower impact in terms of how they are farmed.”

Spencer shares this concern and says Hawaii Oceanic wish to eventually develop other ways of feeding their fish, e.g. by creating food from soybeans or algae. It might also be possible to decrease the need for fish meal by recycling fish oil from the farm itself.

“We’re concerned about the environmental impact of what we’re doing,” Spencer said. “Our whole goal is to do this in an environmentally responsible manner.”

As reported earlier this week, Danish television presenter Lisbeth Koelster was put on trial after deliberately pouring diluted anti-dandruff shampoo into a fish tank housing 12 guppies. The aim of the “experiment” was to demonstrate the level of toxic material in the shampoo. After being subjected to the shampoo, all but one of the fishes died and a Danish veterinarian who watched the show decided to press charges.

Koelster had pleaded not guilty, but the Glostrup court found her guilty of violating animal protection laws. Judge Thomas Lohse said Koelster had “deliberately committed an act of cruelty to animals” and violated animal protection laws. She was however not found to have violated any laws regarding experimentation on animals.

Koelster will not have to pay any fine since the event took place in 2004; four and a half year from now. The judge found this amount of time unreasonable and therefore decided not to fine her.

An important step in the ground-breaking Clean Seas Tuna breeding program was taken today when millions of dollars worth of Southern Bluefin Tuna was airlifted from sea pens off South Australia’s Eyre Peninsula to an on-shore breeding facility at Arno Bay.

The Southern Bluefin Tuna is a highly appreciated food fish and the remaining wild populations are continuously being ravished by commercial fishing fleets, despite the species status as “critically endangered” on the IUCN Red List of Threatened Species.

The Australian tuna breeding program is the first of its kind and will hopefully help ease the strain on wild populations. The air transfer was made to provide the breeding program with an egg supply ahead of the spawning period.

As reported earlier, the Australian company Clean Seas Tuna managed to successfully produce Southern Bluefin Tuna fingerlings in March this year and they are now hoping to commence commercial production of the species no later than October.

WWF Australia’s fisheries program manager Peter Trott says any advancement that would reduce pressure on wild tuna stocks is welcome, but he also cautions against the environmental problems associated with large-scale aquacultures. It is for instance common to use other fish to feed farmed fish, which can put pressure on wild fish populations.

Researchers at Tokyo Institute of Technology have undertaken what is believed to be the very first CT scan of eggs inside a coelacanth fish.

“I was surprised to see that all the eggs were the same size,” said Dr Norihiro Okada, a bioscience professor at the university and a member of the research team. “I hope to do research into why this is.”

Each coelacanth fish was roughly 170 cm (67 in) long and weighed about 70 kg (154 lbs). After being captured off the coast of Tanzania, both fishes were frozen and send to Japan where the CT scan showed how each fish contained roughly 40 eggs; each egg being about 7 cm (almost 2 ¾ in) in diameter.

The eggs of a coelacanth are never released into the water because the offspring hatch while still inside their mother. The young fish sometimes reach a length of 30 cm (12 in) before leaving their mother’s body.

Coelacanths were long believed to have gone extinct around the same time as the dinosaurs, until scientists realized that these fishes actually turn up in the nets of African and Asian fishermen now and then. The first confirmed finding is from 1938 when a specimen was captured in the Indian Ocean.

Coelacanths are of special interest to evolutionary biologists since they are thought to represent an early step in the evolution of fish to amphibians. You can read more about this in our coelacanth article.

A sinking date has now been set for the retired military vessel scheduled to form an artificial reef off Key West in Florida. If everything goes according to plan, Gen. Hoyt S. Vandenberg – a 523-foot-long military ship that used to track Russian missile launches during the Cold War – will be sunk seven miles (11 km) south of Key West on May 27.

“Our sink window opens Wednesday, May 27, and that’s the date we’re currently targeting,” said Jim Scholl, Key West’s city manager and project administrator. “However, there are factors that could delay the scuttling, including weather and other unforeseen circumstances.”

A definite time for the sinking has not yet been set, but the event will probably take place during late morning, officials said.

During the sinking, a one-mile perimeter will be enforced on the water and in the air by the U.S. Coast Guard, the Florida Fish and Wildlife Conservation Commission, and other U.S. law enforcement agencies.

Gen. Hoyt S. Vandenberg is currently waiting in Key West Harbor.