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Archive for the ‘fish’ Category

Teleost fish are unique in that they are able to regenerate many different types of tissues throughout their lives, including cardiac, retinal, and renal (kidney) tissues.  Many of these regenerative abilities occur through the action of stem-cell like populations.  Identifying stem cells in fish may help researchers identify analogous cells in human tissues. 

The ability of some fish to regenerate renal tissues is particularly interesting because there is currently no known kidney or nephron (the functional unit of kidneys) “stem cell” in humans.  A recent paper looked at using zebrafish to try to identify nephron stem cells. 

To find out more, check out my latest post for the Stem Cell Network.

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It’s hard to talk about biodiversity without becoming a little bit depressed at the nature of things.  This month’s catch is the particularly gut-wrenching case of bluefin tuna.

Bluefin tuna can by known by many names, including Atlantic bluefin tuna, northern bluefin tuna or giant bluefin tuna.  They are capable of reaching in excess of 1000lbs with lifespans of around 30 years.  Feeding on smaller fish such as sardines or squids, bluefin tuna are also important predators in the marine food chain.  Unfortunately for them, they are considered a prize food fish in many human cultures, and fetch astronomical prices in the Japanese sushi market.

While bluefin tuna have always been fished, the relatively recent popularity of sushi in Western cultures as well as the advent of seine fishing poses an immense threat to this fish.  Indeed, bluefin populations are approaching collapse in many areas of the world and are already extinct in certain regions. Rough estimates put populations at approximately 30% of historic numbers.

Nature News recently commented on the sad state of the bluefin tuna industry, noting that under-reporting and illegal fisheries are common.

The International Commission for the Conservation of Atlantic Tunas (ICCAT)meets this November 17th in Madrid to discuss the bluefin tuna fisheries and set quotas. But as Nature News noted, this commission has largely been ineffective and a recent report released by the International Consortium of Investigative Journalists (ICIJ) highlights the many faults of this lax and under-regulated industry.

As always, the most effective avenue of change still lies with the consumer.  Eating a species into extinction is just a little bit ridiculous and completely unnecessary.  Add bluefin tuna to your list of seafood no-no’s and check out the Vancouver Aquarium’s Oceanwise program for a list of seafoods that should not be ending up on your dinner plate.

[Photo from http://www.oceanriver.org/AtlanticBluefinTuna.php, original by Chris Park]

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Fish Love

Recently, TED.com broadcast a talk by famed chef and amateur scientist Dan Barber, entitled, “How I fell in love with a fish.”  What’s fish love got to do with animal science?  Surprisingly, quite a bit!  Take a look at this link to view the discussion in full:
Dan Barber talks fish love on TED.com.

Fish farming has been both lauded and criticized by the media, social activists, and foodies worldwide.  On the surface, fish farming seems a natural progression.  Why hunt and gather when you can produce?  It is, after all, based on the model of food production that has sustained much of the First World for the last century.  Fish farming is also a viable alternative to the massive overfishing which has decimated many large-fish stocks, such as tuna and cod.  But is it sustainable?  And perhaps most importantly, is there anything remotely “natural” about it?

Productivity of fish farms is often measured in terms of input-output:  How much input is required to produce a certain output of marketable fish?  Some farmed fish species can achieve conversion ratios of close to 1:1, but for most fish, ratios of between 3  to 1 and 10 to 1 are more common.  Incredibly, tuna requires 15lbs  of input to produce 1lb of marketable fish!  These fish are kept in open-water cages or tanks, restricting their normal swimming habits.  As a result, their water must be continually treated for contaminants and the fish must be fed regularly.   A lot of fish feed is produced from the scraps of the livestock industry.  As Dan points out in his talk, we are eating fish who eat chicken!

Dan then compared this typical agri-business fish farm to an eco-farm operating on the coast of Spain.  This fish farm was created on the marshy, flooded canals off the coasts of Spain .  Here, commercial fish, shrimp and eels are raised in an almost-natural marsh setting.  Instead of controlling for oxygen content, nitrogen levels and contaminant levels, the farm relies on the natural cycling processes of the ecosystem and resident organisms.  Perhaps most amazingly, the fish eat… what fish eat!  Algae, phytoplankton, and even other fish are on the menu.  No chicken dinners here.

As researchers and technicians in animal science, we can draw parallels with how we keep our own animals.  We breed mice in massive numbers, we feed them generic, chemically correct diets, plunk them into sterile cages once a week, and then we wonder – Why do I lose 20-40% of pups?  Why do some breeding pairs fail to produce?

No one is advocating a switch to open field mice breeding.  Clearly ,the nature of scientific experimentation does not allow this.  However, we can ask: What steps can we take to make animal breeding more natural?   Mice, for example, typically build nests and forage for foods.  Excellent options for rodent breeding can include adding nesting materials, providing nutritional supplements, and supplying foraging opportunities.  All of these options work by working with the natural tendencies of the rodent.  This idea can be applied to all animals kept in research colonies.  Whether it is through increased enrichment or improved breeding strategies, we might find that by working with nature, we will have more success than when we try to control it.

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As a family, cichlids are not especially noteworthy. Cichlids are “perch-like” bony fish found all over the world and are most diverse in South America and Africa. Familiar names in the cichlid family include popular aquarium fish such as the angelfish or the discus. Cichlids such as tilapia are also commonly found in the seafood department.

Not so interesting, right?

The Habitat
A more interesting story looks at a subset of the cichlid family, the Lake Malawi cichlids. Lake Malawi is a geologically young lake in the Great Rift Valley of East Africa. Since it hasn’t been around for millions upon millions of years, it’s an amazing example of species colonization and adaptive radiation.

Whenever a new habitat forms, whether it be a volcanic island (like Hawaii!) or the formation of a lake (like Lake Malawi), it is initially barren of life. This is new real estate! But over time, species from neighbouring habitats will, by chance, colonize it. Plants may get blown in, or an errant current may disperse a school of fish, for example.

The Genetics

Due to variation in our genes, no two individuals are the same. By nature, living things tend to have preferences – some tolerate cold temperatures better, while others need more light, for example. Having preferences can be beneficial, ecologically speaking, because it prevents competition between members of a species for the same habitat. And over a LONG time, these preferences can lead to differential mating. For example, if some members of a species preferred brackish water and spent the majority of their time in brackish water, these members are more likely to mate with each other rather than someone on the other side of the lake. This is probability. And finally, over a long LONG time, genetic differences may accumulate due to this preferential mating. And so you have it – from adaptation to different environmental niches, a colonizing species can radiate into many different species, each one specialized to exploit a certain niche.

The Fish
The Lake Malawi cichlids are an amazing example of this process. Species of Lake Malawi cichlids can be readily divided into groups: an open-water, sand-swelling group and a rock-dwelling group. Within these two general types, hundreds of species – each slightly different from the other – have been defined. Many more are thought to be still be undiscovered!

And, it isn’t over. Estimates have placed the origin of the Lake Malawi cichlid diversification at 10,000 years ago, or less. On a geological scale, this is nothing. Genetically, this means that there is not yet a great deal of difference between different cichlid species. As such, many different cichlid species are still able to hybridize with each other where niches overlap or when placed in a laboratory setting. Aquarists take advantage of this, for example, to breed fish with different colours and patterns.

This pattern of colonization and subsequent radiation is found repeated in many other species and habitats. Check out a few other famous examples in the silverswords of Hawaii or the finches of Galapagos!

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