Tuesday, 29 May 2012

Four continents and a fish

As a child in the seventies, I remember clutching my grandfather’s arm and marvelling at Tilapia being reared in a shallow pond in his land in a South Indian village. Many years later, one summer in the late nineties, in an oriental store in Ohio, USA, I was introduced to a packet of frozen fish which turned out to be Tilapia. Needless to say, I enjoyed it much and felt that it was one of the most delicious fishes I had ever eaten.

Fast forward to 2010… in a lakeside restaurant by the Sea of Galilee, in Israel, we were served St. Peter’s fish which was delectable. St. Peter’s fish is so named after the account in the gospel of St. Matthew where Jesus asks His disciple Peter to catch a fish, open the mouth of the fish, and find the coin that is to be paid as taxes. It turns out that St. Peter’s fish was indeed Tilapia. The species of the fish in Israel carries its small young in its mouth until large enough to survive on their own. The fish also seems to have a penchant for shining objects and is known to pick up small pebbles and bottle caps from the lake floor. In the idyllic restaurant by the Sea of Galilee, our tour guide repeatedly threw pieces of bread into the water and we could see Tilapia shoaling in and catching the food, vying with hoards of kittens and cats perched on the rocks that had learnt to traverse the shallow waters. Later I learnt that St.Peter’s fish has been used in small-scale low-technology commercial or subsistence fishing practices in that area for thousands of years.

I had forgotten all about Tilapia until recently I read the correspondence in Nature by Vitule et al arguing against the proposed law that, if implemented, would lead to the culture of invasive non-native species of Tilapia and other fishes in cages in dammed areas in Brazil.

The name ‘Tilapia’ is used loosely to describe over hundred species of cichlid fish from the tilapine cichlid tribe. Cichlids are most diverse in Africa and South America. The native cichlids in Asia are restricted to very few species in Israel, Iran, India, Syria and Sri Lanka. Other cichlids include fishes commonly grown in aquariums like the angel fish and discus. Tilapia seems to be highly resilient in the nature of its habitats-living in ponds, streams, lakes and rivers. Due to their ease of farming, size, protein content and taste they are among the top ten fish used in farming. Tilapia meat which is a good protein source, low in saturated fat, and calories does not accumulate mercury. Tilapia can effectively controls algae which they feed upon and replaces the need for the use of chemical algaecides. In Africa, they control pests such as mosquitos. Whilst native species are rich in nutrients, farmed species have low levels of omega 3 fatty acids due to their diet. Additionally, farmed fish are fed with hormones such as testosterone which may have endocrine disrupting effects in the food chains.

Whilst tilapia require warm waters to survive and cannot live in natural temperate habitats (indicating that farming of tilapia in controlled conditions may not disrupt the native species if accident release does take place), such a situation could be catastrophic in the long run in the tropical areas by leading to the disruption of native fish species. In Lake Victoria, introduction of the Nile Tilapia led to the disappearance of two native species. The alien species has a higher growth and fecundity rate compared to the native species. Rightly, Tilapia is listed in IUCN’s compendium of invasive alien species.

Farming of native species of Tilapia is beneficial as long as it is subsistence and sustainable farming. However, current aquaculture practices of non-native fishes often involves aggressive farming methods. Further culture of non-native species in cages in natural water bodies might pose significant risk to containment which could be compounded in sub-tropical and tropical environments where escape would lead to colonisation and disruption of the already fragile ecosystems. J.R.S. Vitule, the lead author of the correspondence in Nature from Laboratório de Ecologia e Conservação, Paraná, Brazil, whose research focuses on the conservation of the endemic freshwater fishes of the Atlantic rain forest and the management of non-native fish species that threaten their survival, says ‘Fish escapes are inevitable, and cage aquaculture may create a constant flow of propagules into the wild, establishment, spread and invasions’ (Personal correspondence with Dr. Vitule). Other issues relate to the release of nutrients such as fish feed that can lead to water pollution and also potential endocrine disruption (Ortiz -Rodas et al, 2008), a topic requiring further investigation. The debate continues……


Image source: Sarah Stephen (image shows a typical St. Peter’s fish lunch in the Sea of Galilee)

Monday, 28 May 2012

Aquaculture of non-native fish species

What are your views on the aquaculture of non-native fish species?  Please find a survey on the side bar of this blog where you can make your voice heard.

Friday, 25 May 2012

When introductions go bad

My first sighting of the red squirrel was in Camperdown Park in Dundee in 2003. I remember that scene vividly. I had since tried desperately to see this elusive animal again but to no avail, save a brief sighting, again in Camperdown Park, in Autumn 2010. This is because although red squirrel, which is native to UK and  is  protected in Europe, is outnumbered by its foreign relative, the grey squirrel that was introduced to the UK from America. Grey squirrel has several competitive advantages including its resistance to squirrel parapox virus which is fatal to the red (grey squirrels are vectors), increased fecundity, and greater ability to digest a wider variety of food. In fact, the future of the red squirrel in the British Isles is rather precarious. The Forestry Commission estimates that there there are only 140,000 red squirrels compared to over 2.5 million greys.

Recently during a holiday near Lake Geneva, Switzerland, I encountered 2 red squirrels and 1 black squirrel  (resembled the red squirrel with respect to the ear tufts, but with a black/grey rather than red coat). You can see a video here in Youtube:  http://www.youtube.com/watch?v=g4SqcK9CME8

There is a lot of debate on how the introduction of alien species can affect the native species and tilt ecosystems, but studies indicate that certain ecosytems could be more vulnerable that others. As early as 1958, Charles Elton claimed that ecosystems with higher species diversity were less subject to invasive species as there are  fewer available niches. A recent paper by Eisenhauer et al shows that species diversity could stabilise communities during invasions. It appears as if biodiversity of ecosystems provides increased resilience against onslaughts including that by foreign invaders. Caution should be exercised when foreign species are introduced. In light of these observations, a  proposed law in Brazil is of importance. A recent correspondence in Nature by Vitule et al (May 2012) warns of the repecussions of a new law that, if approved, would allow farming of foreign fish species in cages. The fishes that are being considered for introduction are tilapia and carp. The authors warn that the indigenious aquatic ecosystem would be disrupted if these  introduced species were to escape and would jeopardise the aquatic biodiversity which is already fragile due to  human activities such as pollution and construction.

Vitule JR (2012). Ecology: Preserve Brazil's aquatic biodiversity. Nature, 485 (7398) PMID: 22596145
Eisenhauer N, Scheu S, & Jousset A (2012). Bacterial diversity stabilizes community productivity. PloS one, 7 (3) PMID: 22470577

Red Squirrel image source: Sarah Stephen

Monday, 21 May 2012

Sugar gliders

I must confess that a degree in Zoology was not of use when I came across some new items on this adorable creature. And keeping on with the ongoing theme, here is another Australian marsupial (admittedly, an inhabitant also of Tasmania, Papua, Indonesia, New Guinea and Bismarck Archipelago).

Sugar gliders (Petaurus) are gregarious, nocturnal possum/marsupials (i.e babies developing in the marsupium). At one glance, one may mistake it for a flying squirrel (Ratufa) due to its webbed patagium which allows it to glide from tree to tree. Their name originates from their predilection towards anything sweet, especially tree saps and nectar, and unsurprisingly, they live in eucalyptus and acacia forests.

They are currently in vogue as exotic pets. In parts of Australia, one needs a permit to keep them and Malaysia (which gets its sugar glider population mainly via illegal trade from Indonesia) is considering covering the species under their conservation Acts.

Remarkably, their gestation period is only 15-17 days. If only research papers too were!

Image Source: Joe McDonald





Tuesday, 8 May 2012

A small step for koalas

I have been following certain developments on the koala front in Australia. The marsupial is an icon associated with Australia- and is also well known for its predilection for eucalyptus and sleep.

After a decline in the wild population (to approx. around 200,000 according to government figures), Tony Burke (Australia’s Environment Minister), following a Senate report, has listed koalas as ‘vulnerable’ species last week. However, the tag will be restricted to certain areas- i.e Queensland, New South Wales (both states experienced a heavy decline in population), and Australian Capital Territory (which now has no wild koalas), which is another example of effective lobbying by the industries concerned as both Victoria (which has the distinct Strzelecki koalas, most of which are in private properties) and South Australia are not included (Burke claims that there are large koala populations in these two states). Whilst NSW welcomed this development, the Queensland Premier, Campbell Newman, is disgruntled, labelling the move as a ‘mindless green tape’ and threat to the employment market and development in the state.

The Senate report associated the population decline with habitat destruction (mainly by coal mining, logging, and housing developments), climate change (drought and extreme weather resulting in bushfires), accidents (road-kill), attacks by dogs (especially in summer when they venture into gardens to drink from swimming pools and water bowls), and disease (notably: Chlamydia). In the case of bushfires, koalas’ slow-moving nature prevents them from escaping from fires.

The question now remains as to what will be done proactively to ensure that the koala isn’t driven to extinction.

Image source: BSPI/Corbis
















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