Now this is an interesting development! Two female zebra sharks, located at the Vinpearland Park Nha Trang, laid eggs without the need for male sharks! After a long wait of 5 months of incubating the eggs, the very first unisex baby shark was born!

Zebra Shark Pup

The tank where the two female sharks have made their home for the past year has no male sharks in it. However, the first female shark, much to the surprise of the keepers, laid her eggs and a baby shark was born near the end of June.

The Oceanography Institute researchers in Nha Trang have explained that this is a very rare occurrence in nature and this is the very first time that a unisex shark has made an appearance in Vietnam. Not to be outdone by her tank partner, the second female shark laid close to a dozen eggs, of which over half of them didn’t have citellus. The others with citellus can actually develop embryos, and, with great excitement, the scientists at the Vinpearland Park are incubating these eggs to see what develops.

An expert at the Oceanography Institute has shed some light on the aspects of asexual reproduction. They explained that asexual reproduction occurs when the eggs develop an embryo without any interaction, or contact with sperm from a male. This is rather common in the insect world, however it is extremely rare is fish and reptile species, and has never been seen before in any kind of mammal. “Until now sharks have not been listed as animals with asexual reproduction. This phenomenon has only been recorded once in the US and only a few times around the word. We need to perform a DNA test to verify what happened,” the scientist continued.

A team of scientists at the Michigan State University has found a new, more efficient method for cloning zebra fish.

“After the mouse, it is the most commonly used vertebrate in genetic studies,” said Jose Cibelli, an MSU professor of animal science and one of the paper’s co-authors. “It is used in cancer research and cardiovascular research because they have many of the same genes we have.”

Zebra fish is also used by scientists researching normal development and birth defects, as well as various human diseases and the functions of cell populations within organs.

Up until now, zebra fish cloning has had a low success rate, but the new Michigan method has changed this. The new method uses ovarian fluid from a Chinook salmon to keep the unfertilized egg alive.

“This worked well, because it kept the egg inactive for some time”, Cibelli explained. It gave us two or three hours to work with.

During the next step of the process, the Michigan researchers used a laser to remove DNA from the egg; a method borrowed from human in vitro fertilization. Next, the team devised a new, more efficient way of inserting the donor cells into the egg.

“The tricky part was finding a way to get into the egg,” Cibelli said. “We used the same entrance that sperm uses. There was only one spot on the egg, and we had to find it.”

You can find more information in the most recent issue of the journal Nature Methods.

The main author of the article “Novel Somatic Cell Nuclear Transfer Method in Zebra Fish,” is Kannika Siripattarapravat, a doctoral student in Cibelli’s Cellular Reprogramming Laboratory. Other authors include Patrick Venta, an associate professor of microbiology and molecular genetics, and C.C. Chang, a professor of pediatrics and human development.

In several species of fish, such as the cichlid species Neolamprologus pulcher, it is common for subordinate females to help an unrelated dominant breeding pair raise their young. The reason behind this seemingly altruistic behaviour, known as alloparental care, has puzzled scientists for many years and one of the most widely spread hypotheses put forward has been the ‘pay-to-stay’ hypothesis. According to the ‘pay-to-stay’ rationale, the subordinate female helps out the dominant pair just to be able to stay in the group. Not being ostracised from the group augments her long-term survival chances, thus increasing the chance for her to live long enough to eventually obtain a breeding position.

Picture by: JJPhoto.dk

A new study carried out by Dik Heg and coauthors does however bring forth a new hypothesis: the substrate rationale. In their study, Heg and his colleges tested the hypothesis that subordinate female cichlids are helping dominant pairs in return for a more immediate direct reproductive benefit. After a series of experiments where the total number of eggs produced over a 30 day period by dominant and subordinate Neolamprologus pulcher females were carefully counted, researchers found that a subordinate female helping out a dominant pair was more likely to produce eggs herself compared to other subordinate females.

According to Heg and coauthors, the most likely reason for the increased reproductive success of “fish nannies” is that the subordinate female gains access to the breeding substrate.

If you wish to read more, see the paper “Heg, D, E Jutzeler, JS Mitchell and IM Hamilton (2009) Helpful female subordinate cichlids are more likely to reproduce”. It has been published in the journal PLoS ONE.

Here at AC Tropical Fish, we believe in the Jude Law-hypothesis. The dominant female will naturally snatch away the most prosperous male, but by posing as a benevolent nanny even a subordinate female can gain access to his home and hope for some of his triumphant DNA to eventually find its way into the genetic make up of her own offspring.

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.

An expansion of vertical seagrass occurring some 25 million years ago was probably what prompted seahorses to evolve from horizontal swimmers to upright creatures. If you live in vertical seagrass, an upright position is ideal since it allows you to stay hidden among the vertical blades.

This new idea is put forward in a report by Professor Beheregaray* and Dr Teske** published in the journal Biology Letters on May 6.

Sea horse picture from our Seahorse section.

Only two known fossils of seahorse have been found and this scarcity of fossil records has made it difficult for scientists to determine when seahorses evolved to swim upright. The older of the two fossils is “just” 13 million years old and no links between the two fossils and horizontally-swimming fish has been found.

“When you look back in time, you don’t see intermediate seahorse-like fish,” Beheregaray explains. There are however fish alive today that look like horizontally-swimming seahorses and Beheregaray and Teske have therefore studied them in hope of finding clues as to when seahorses made the transition from horizontal to vertical swimming.

By comparing DNA from seahorses with DNA from other species of the same family, Beheregaray and Teske were able to determine who the closest living relative to seahorses was.

“The pygmy pipehorses are by far the most seahorse-like fish on earth, says Beheregaray. “They do look like the seahorses, but they swim horizontally“.

When you have two closely related species, you can use molecular dating techniques to calculate when the two species diverged from each other. Beheregaray and Teske used a molecular dating technique that relies on the accumulation of differences in the DNA between the two species, and then used the two existing fossils to calibrate the rate of evolution of DNA in their molecular clock. By doing so, the two researchers could conclude that the last common ancestor of seahorses and pygmy pipehorses lived around 25 to 28 million years ago. At this point, something must have happened that led to the formation of two distinct species, and Beheregaray and Teske believe that this “thing” was the expansion of seagrass in the habitat where seahorses first evolved.

The time in history when seahorses arose, the Oligocene epoch, coincided with the formation of vast areas of shallow water in Austalasia. These shallow waters became overgrown with seagrass and turned into the perfect habitat for upright swimming seahorses that could remain hidden from predators among the vertical blades. The pygmy pipehorse on the other hand lived in large algae on reefs and had no use for an upright position, hence it continued to swim horizontally just like their common ancestor.

“The two groups split in a period when there were conditions favouring that split,” says Beheregaray. “It’s like us. We started walking upright when we moved to the savannahs. On the other hand, the seahorses invaded the new vast areas of seagrass.”

* Associate Professor Luciano Beheregaray of Flinders University

http://www.flinders.edu.au

** Dr Peter Teske of Macquarie University

http://www.macquarie.edu.au

A study of the molecular phylogenetic interrelationships of south Asian cyprinid genera Danio, Devario and Microrasbora has resulted in a reclassification of the group and the creation of a new genus: Microdevario.

The study, which has been published in a recent issue of the journal Zoologica Scripta, was carried out by Fang Fang and his colleges at the Swedish Museum of Natural History.

The researchers examined the molecular phylogeny of the Danioninae using fragments of the mitochondrial cytochrome b and nuclear rhodopsin genes from 68 species, including 43 danioinine species.

The analysis revealed the species Microrasbora rubescens and the genera Chela, Laubuca, Devario, and Inlecypris to form a natural group, the Devario clade, with the species Microrasbora gatesi, Microrasbora kubotai and Microrasbora nana being in sister group position to the rest.

Zebrafish

These findings, in combination with subsequent analysis of morphological characters, have made the authors propose four taxonomic changes:

· The species Inlecypris auropurpurea is reassigned as Devario auropurpureus.

· Microrasbora gatesi, Microrasbora kubotai and Microrasbora nana are reassigned to a new genus named Microdevario. Fish of this genus are distinguished from other danioinines by a combination of skull and jaw characters.

· Reassignment of the species Celestichthys margaritatus to the genus Danio in previous studies is confirmed.

· The membership of Chela is restricted to Chela cachius. All other species previously placed in this genus are reassigned to the genus Laubuca, except Chela maassi, which is in the genus Malayochela.

For more information about the study and the suggested taxonomic changes, see the paper Fang, F, M Norén, TY Liao, M Källersjö and SO Kullander (2009) Molecular phylogenetic interrelationships of the south Asian cyprinid genera Danio, Devario and Microrasbora (Teleostei, Cyprinidae, Danioninae). Zoologica Scripta 38, pp. 237–256.

New research has revealed that the tapetail, bignose and whalefish are in fact all the same fish.

For decades, three different names have been used for three very different looking underwater creatures: the Tapetail, the Bignose and the Whalefish. A team of seven scientists*, including Smithsonian curator Dr Dave Johnson, has now discovered that these three fishes are in fact part of the same family.

After studying the body structures of the tapetails (Mirapinnidae), bignose fish (Megalomycteridae) and whalefish (Cetomimidae) and taking advantage of modern DNA-analysis, the team realized that the three are actually the larvae, male and female, respectively, of a single fish family – Cetomimidae (also known as Flabby whalefish).

“This is an incredibly significant and exciting finding,” says Johnson. “For decades scientists have wondered why all tapetails were sexually immature, all bignose fishes were males and all whalefishes were females and had no known larval stages. The answer to part of that question was right under our noses all along—the specimens of tapetails and bignose fishes that were used to describe their original families included transitional forms—we just needed to study them more carefully.”

If you wish to find out more, the article “Deep-sea mystery solved: astonishing larval transformations and extreme sexual dimorphism unite three fish families” has been published in the journal Biology Letters by the Royal Society, London.

http://publishing.royalsociety.org/

http://journals.royalsociety.org/content/g06648352k5m1562/

* The seven scientists behind the discovery are:

G.David Johnson, Division of Fishes, National Museum of Natural History, Smithsonian Institution, Washington, DC 20560, USA

John R. Paxton, Ichthyology, Australian Museum, Sydney, New South Wales 2010, Australia

Tracey T. Sutton, Virginia Institute of Marine Science, Gloucester Point, VA 23062, USA

Takashi P. Satoh, Marine Bioscience, Ocean Research Institute, University of Tokyo, Nakano-ku, Tokyo 164-8639, Japan

Tetsuya Sado, Zoology, Natural History Museum and Institute, Chuo-ku, Chiba 266-8682, Japan

Mutsumi Nishida, Marine Bioscience, Ocean Research Institute, University of Tokyo, Nakano-ku, Tokyo 164-8639, Japan

Masaki Miya, Zoology, Natural History Museum and Institute, Chuo-ku, Chiba 266-8682, Japan

Australian scientists have now completed an 18-month long project aimed at scientifically describing sharks and rays, using traditional techniques as well as modern DNA sequence analysis. The ambitious project has resulted in over 100 species of sharks and rays being properly classified, which is equal to about one third of Australia’s known sharks and rays.

Southern Dogfish Image credit – CSIRO

Over 90 of the new species had already been identified by Dr Last and Dr Stevens in their book “Sharks and Rays of Australia” from 1994, but remained undescribed and without scientific names.

Many of the new species are endangered in the wild, such as the Maugean Skate and the Southern Dogfish, and having them properly classified and named is important for future monitoring and conservational work. The new descriptions and names will be included in a revised edition of “Sharks and Rays of Australia” which is planned for release in 2009.

Maugean Skate Image credit – CSIRO

The 18-month long study was backed by CSIRO’s Wealth from Oceans National Research Flagship. National Research Flagships are large-scale multidisciplinary research partnerships and the National Research Flagships program is one of the biggest scientific research endeavours ever undertaken in Australia.

If you’re interested in the Wealth from Oceans Flagship, you can find more information here. http://www.csiro.au/org/WealthOceansFlagship.html

When Kate Stoeckle, 18, and Louisa Strauss, 17, collected samples of fish from New York fish stores and restaurants on Upper Manhattan and tested them using the new genetic barcoding method, an astonishingly large portion of the samples turned out to be mislabelled and sold under the wrong name. A sushi restaurant claiming to offer white tuna was for instance serving their guests Mozambique tilapia instead, while another restaurant sold Spotted goatfish from the Caribbean Sea under the name Mediterranean red mullet.

Red Snappers

All in all, Stoeckle and Strauss collected 60 different samples of fish and had them tested at the University of Guelph in Canada. Four samples could not be identified by the genetic barcoding identification technique, but of the remaining 56 samples no less than 14 turned out to be mislabelled. This means that out of 56 samples, a whooping 25 percent were sold under false pretences.

All 14 cases of mislabelled fish consisted of comparatively cheap fish being sold as a more expensive species. It is therefore hard to see how the mislabelling could be the result of honest mistakes by fishermen or middlemen.

Not getting what you pay for as a consumer is however not the only problem with mislabelled fish; a false identity can also be used to sell endangered species to unsuspecting dinner guests. In the Stoeckle and Strauss study, two samples of alleged red snapper did for instance turn out to be endangered Acadian redfish (Sebastes fasciatus). The Acadian redfish has been listed as Endangered (EN) on the IUCN Red List of Threatened Species since 1996.

The study did not unveil the names of the restaurants and fish shops since it could not be determined if they were intentionally misleading their customers or if they had purchased the mislabelled fish in good faith.

Stoeckle and Strauss are both students at New York’s Trinity school.