User:Bellamorphosis/Ichthyodinium chabelardi

 Ichthyodinium chabelardi 

Ichthyodinium chabelardi is a parasitic species of dinoflagellates from the class Syndiniophyceae. This species affects young developmental stages of marine life by targeting their embryos and larvae. According to Baldauf (2008), dinoflagellates belong to the supergoup Alveolata. As a recently discovered group of protists, these organisms differ from the other supergroups by their fluid filled sacs located below the cell membrane. The clade Syndiniophyceae consists of five marine endoparasites known as MAL I, MAL II, MAL III, MAL IV and MAL V. The genus Ichthyodinium belongs to MAL V.

Most dinoflagellates are photosynthetic while approximately half are heterotrophic. Some heterotrophic species consist of non-photosynthetic organelles which includes: Syndiniophyceae and Noctiluciphyceae. The class Syndiniophyceae consists of mostly endoparasitic protists with some undiscovered species. As a result, they exhibit strange physiological behaviors in their aquatic habitats making them difficult to recognize by their class. Exclusively, they parasitize marine organisms such as ciliates.

This species is ubiquitous and can be found in different water bodies around the world especially fish farms. It poses a threat to the commercially significant fish species including the native species belonging to specific regions.

Description
In the beginning, I. chabelardi was correctly identified as a syndinid. Even today there are still controversial views on the placement of I. chabelardi in the phylogenetic tree. Some believe it belongs under the Perkinsoza class based on genetic analysis obtained. However, after further observations of its phenotype, it was discovered that it shares similar morphology with other dinoflagellates. For example, I. chabelardi may have features that resemble dinospores, trichocysts, or even condensed chromatin during mitosis found at different trophic stages in dinoflagellates. Still, not much is known about this parasitic species.

Life Cycle
I. chabelardi infection varies on the host species. In some hosts, the schizonts may reach the second generation while, in other hosts, infection may reach the third generation. Thereafter, they release spores which swim to transmit their infection to other marine organisms. There are two different stages of the schizonts; the primary and the secondary stages.

Primary schizonts
These are the small, transparent, unicellular forms of the parasite not growing more than 20 micrometers in size. Usually, up to 3 schizonts can be found on the yolk sac of fish eggs. Upon infection of the yolk sacs, they penetrate the eggs by absorption of the outer layer of the host egg. Following this, the nucleus undergoes mitosis and the cytoplasm encapsulates each newly formed nucleus forming secondary schizonts.

Secondary schizonts
After the formation of the secondary schizonts, they become separated into 20 micrometer cylindrical structures which begin accumulating lecithin in their structures. The reason for this is unknown. After separation and growth of these individual structures, they start diving by mitosis partitioning into two longitudinal forms. Meanwhile, two sister cells are still attached to each other by their posterior ends (poles) forming a triangular structure. Afterward, the sister cells form layers of long cords containing about 8 cells per cord with a length ranging between 1-2 mm.

Tertiary schizonts
During this stage, the schizonts detach themselves from the cords and undergo mitosis again to form spherical structures. Moreover, the yolk sacs of the fishes appear to be non transparent because of the single nucleus parasitic stages found in them. These tertiary schizonts develop into zoosporangia which is hatched and released into the surrounding water around the host. After hatching, this infective stage of the parasite may lead to the rupture of the yolk sac and eventually, the death of the early larval stage. The release of the parasite may vary at times. In some cases, it may be released after the larvae hatches while, in other cases it may be released at least 10 hours later.

Transmission and Host range
When these spores are in the water, they tend to develop certain features such as flagellates through mitosis and they then develop large trichocysts similar to Syndiniales helping them attach themselves to other hosts. The nucleus of the spores appear to have participated in early stages of mitosis because of their condensed chromatin structures found in their DNA. Some of the developmental stages of the spores even resemble the developmental stages of some Apicomplexan parasites. The parasitic spores survive outside of their hosts for only a few days but will eventually die since they are not free-living organisms. There is evidence that this parasite does not penetrate but passes through female reproductive opening before it closes up.

This parasite is considered as a pest to fish farms around the world and fish eggs such as salmon. They tend to parasitize commercially significant fish species such as:


 * Risso
 * Gilt-head sea bream for example boops boops
 * Horse mackerel
 * European anchovy
 * Cod
 * European eel

Geographical distribution
I. chabelardi can be found everywhere in the oceans. Regions in which the parasite has been found are as follows:


 * Southern part of China's waters
 * Southern Pacific ocean
 * North-eastern Atlantic ocean
 * Mediterannean Sea

Moreover, they tend to prefer the warm and temperate parts of the oceans.