Adaptations and diversity of Antarctic fishes



by   |  VIEW 153

Adaptations and diversity of Antarctic fishes

Adaptations and diversity of Antarctic fishes: A Genomic Perspective, research published on the Annual review of animal biosciences, tries to give an answer to this interesting retrospective. The researchers explain: "Antarctic notothenioid fishes are the classic example of vertebrate adaptive radiation in a marine environment.

Notothenioids diversified from a single common ancestor ∼22 Mya to between 120 and 140 species today, and they represent ∼90% of fish biomass on the continental shelf of Antarctica. " Then they added: "As they diversified in the cold Southern Ocean, notothenioids evolved numerous traits, including osteopenia, anemia, cardiomegaly, dyslipidemia, and aglomerular kidneys, that are beneficial or tolerated in their environment but are pathological in humans.

Thus, notothenioids are models for understanding adaptive radiations, physiological and biochemical adaptations to extreme environments, and genetic mechanisms of human disease." Researchers concluded: "Since 2014, 16 notothenioid genomes have been published, which enable a first-pass holistic analysis of the notothenioid radiation and the genetic underpinnings of novel notothenioid traits.

Here, we review the notothenioid radiation from a genomic perspective and integrate our insights with recent observations from other fish radiations." An example of Antarctic fish are the Channichthyidae. They have an elongated body that tapers towards the tail.

The head is large with a pointed muzzle and very large eyes. The pectoral fins are well developed, the ventral fins are long and rigid, the anal fin is thin and barely visible, the tail broad and muscular. On the back they have two dorsal fins, the first with strong developed rays.

Cannictidae lack a swim bladder. Icefish are unusual in many ways, lacking scales and having transparent bones, but what most sets them apart among vertebrates is their hemoglobin-free white blood. These fish manage to survive in Antarctic waters, the temperature of which fluctuates between -1 and -2 ° C, as their blood has a reduced viscosity.

To reduce blood viscosity, cannictids have evolved by eliminating both red blood cells and hemoglobin, taking advantage of the fact that in low-temperature water oxygen is much more soluble and tends to be absorbed by the gill blood more easily.

Furthermore, these fish carry out skin respiration: they have a dense network of capillaries near the skin, devoid of scales, where a further exchange of gases with the environment can then take place. Evolutionary adaptations fundamental to their survival have been found in the genome of an icefish species.

Some were common to red-blooded fish living in Antarctic waters, such as the presence of additional genes involved in protection from freezing damage, such as antigel glycoproteins and zona pellucida proteins. Others were more closely related to the lack of red blood cells, such as genes than encoding enzymes active in the control of cellular redox state, including members of the sod3 and nqo1 gene families that protect tissues from highly reactive free oxygen in the blood. They are among the few fish that live in the waters of Antarctica.