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Wednesday, December 1, 2010

Ikan Yang Bisa Berubah Ukuran Tubuhnya


Hewan dan manusia bisa bertambah bobot dan lebih gemuk dan mengurus tergantung asupan makanan yang dikonsumsi. Namun, apa yang terpikir di kepala Anda saat ada hewan yang tubuhnya memendek dan memanjang sesuai dengan musim. Ada lho ikan yang bisa berubah-ubah ukuran tubuhnya seperti itu.

Fenomena langka itu menjadi topik peneliti dari Finlandia dan Norwegia yang hasil penelitiannya dipublikasikan dalam jurnal Functional Ecology. Ini merupakan peneliti dari dua negara tersebut, juga merupakan fenomena pengecilan tubuh pertama yang ditemukan pada ikan.

Para peneliti mengungkapkan, pengecilan itu terjadi saat musim dingin. Mereka mendeskripsikan, pengecilan atau penyusutan ukuran tubuh ikan itu dipicu oleh sebuah kondisi yang dinamai over winter anorexia, saat di mana nafsu makan ikan tersebut menurun drastis kala musim dingin.

Untuk sampai pada kesimpulan tersebut, tim peneliti yang dipimpin  Ari Huusko dari Finnish Game and Fisheries Research Institute di Paltamo melakukan percobaan dengan kelompok salmonid, seperti ikan salmon dan trout. Para peneliti tersebut membuat kolam eksperimen yang telah didesain sedemikian rupa sehingga memiliki kondisi seperti musim dingin di wilayah subtropis.

"Kami dihadapkan pada fakta yang tak terduga dan belum pernah didokumentasikan sebelumnya. Ikan benar-benar mengecil dalam kondisi musim dingin. Salmon muda menunjukkan pengecilan ukuran tubuh yang signifikan, sebesar 10 persen dari panjang tubuhnya," kata para peneliti dalam publikasinya.

Peneliti belum mengetahui secara pasti mekanisme biologis yang menyebabkan pengecilan tubuh itu. Namun, peneliti menduga bahwa hal tersebut berkaitan dengan berkurangnya cairan, seperti gel, yang terdapat di tulang belakang yang memicu pengecilan ukuran tubuh.

sumber: KOMPAS.com


Fish shrink during harsh winters

In winter, young wild trout tend to shelter from energy demanding conditions

Fish can shrink during particularly harsh winters, according to researchers.

The scientists, based in Norway and Finland, discovered that juvenile brown trout reduced in length by as much as 1cm - a shrinkage of approximately 10%.

They say this could help the young fish to conserve energy when food is in short supply.

They describe, in the journal Functional Ecology, how the fishes' bodies "shortened".

This rare phenomenon has been seen before in some small mammals, including shrews, and in lizards.

The most dramatic example is the marine iguana. This cold-blooded (or ectothermic) reptile lives in the Galapagos archipelago.

It has been found to shrink as much as 20% of its body length over the years of El Nino events when food availability dramatically decreases due to considerable temperature increase.

But this is the first study to show that fish can shrink.

The scientists described the condition that leads to this shrinkage as "over-winter anorexia" - whereby their appetite decreases dramatically over the autumn "transition period".

The team, led by Ari Huusko from the Finnish Game and Fisheries Research Institute in Paltamo used hatchery-raised salmonids - a group of ray-finned fish that includes salmon and trout.

They created experimental pools in which to study them.

To simulate the conditions of a cold winter, the water temperature and current were controlled and a covering was added to mimic ice coverage.

"We were faced with unexpected and previously undocumented observations... indicating that fish do shrink in harsh winter conditions," the researchers wrote.

"Young salmonids showed significant shrinking of individual body length, up to 10% of the body length, over the course of winter."

Shrinking mystery

The scientists do not yet know exactly what causes the shrinkage.

But they think that, like in shrews, it could be caused by a reduction in the volume of a jelly-like substance within vertebral discs of the creatures' spinal columns.

"This leads to flattening of these formations and thus into the shortening of the spinal column, and hence body length," the scientists explained in the Functional Ecology paper.

Dr Huusko told BBC News: "The apparent triggers for shrinkage were food and feeding stress in connection with environmental conditions generally poor for growth and survival.

"[This] raises several further questions about what kind of consequences shrinkage can have."

source: BBC


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