Arofanatics Fish Talk Forums  

Go Back   Arofanatics Fish Talk Forums > Arowana Forum > Arowana Discussion > Articles, Resources & FAQs

 
 
Thread Tools Display Modes
Old 13-08-2005, 02:50 PM   #1
archie2000
Guest
 
Posts: n/a
Default Aro colouration and food

We all know feeding mp and carotene based food are good for our aros. I was curious and think you would too, would like to find out more on the development of colouration of our aros. Be it pearl, silver, green, banjar, red, xb, etc.. How does the aro scales produce colours and what food and why its good for colouration.

Below are 2 articles that I've came across during my search on this topic.

Coloration is controlled by the endocrine and nervous system, but dietary sources of pigment also play a role in determining color in fishes. The endocrine and nervous system both influence coloration in fish. The pituitary gland secretes hormones that direct the production and storage of pigments throughout the life of a fish, and particularly as maturity is reached. Pigment production and storage often increases at the onset of maturity. Many species use color to provide camouflage and attract a mate. The autonomic nervous system directs rapid color changes in response to stimuli such as a predator or an aggressive tankmate. Anyone who has observed fish knows this color change can occur at a spectacular rate.

Specialized pigment containing cells called chromatophores are located beneath the scales. These cells are branched, permitting pigment granules to be near or away from the surface and aggregated or dispersed. These cells are the reason for the variable and sometimes rapid changes in fish color. Additionally, colorless purine crystals are contained in specialized chromatophores called iridophores. These crystals are too large to move in the iridophores but are stacked to provide a reflecting surface and the base or structural coloration of fishes. The iridophores are responsible for the silver sheen, particularly of small pelagic fish. These cells are capable reflectors of light and are responsible for the counter shading effect where fish appear darker when viewed from above and lighter when viewed from below. This mechanism helps detour predation.

Pigments are characterized by their colors. Carotenoid pigments are red and orange. Xanthophylls are yellow. Melanin pigments are black and brown. Phycocyanin is the blue pigment derived from blue-green algae. Cells containing yellow pigments overlying those containing blue pigments can produce green hues. Fish are capable of producing some pigments, but others must be supplied in the diet. Black and brown pigments are produced in cells called melanocytes. Fish are incapable of producing carotenoid and xanthophyll pigments. Therefore, these must be supplied in the diet.

Spirulina algae is a source of pigments to enhance blues.

Natural sources of pigments are available in the diets of most fish. Color enhancing diets may contain additional natural pigments to enhance colors of ornamental fishes. The carotenoid pigment found in most marine and a few freshwater invertebrates is astaxanthin. This pigment gives the characteristic color to the flesh of salmon and is available in the diet of aquarium fish in shrimp and krill meals and salmon (fish) meal used as sources of protein in some feeds. Pure astaxanthin or canthaxanthin (synthetic astaxanthin) may also be added to fish feed to enhance red and orange coloration. Xanthophylls (yellow pigments) are found in corn gluten meal and dried egg that may be added to the diet to enhance yellows. The ground petals of marigold flowers have also been used as a source of xanthophylls. The blue-green algae spirulina is a rich source of phycocyanin and may be added to a diet to enhance blue coloration. The expense of supplementary pigments often limits the amount used in tropical fish feeds. These natural sources of pigments are in contrast to several methods routinely used to enhance colors of ornamental fish.

Genetics

Let's just take the colour red as an example. Colour is produced in a similar way to photographs in newspaper where from a distance, a photograph will look detailed, well defined, and clear. Yet under closer examination, particularly through a magnifying glass, the picture consists of thousands of tiny dots of ink, each working together to produce a picture of dark and light areas. Skin pigmentation is caused by dots (colour cells called chromatophores) the intensity of which is determined by how densely the dots are packed and how intensely each dot is coloured.

An aro's genetic code will determine both factors, with the role of colour enhancement through feeding only being able to improve the colour of each colour cell (rather than increase their density in the skin). However, there is always hope as that same genetic code will also code for colour development where pattern and the appearance of other chromatophores may develop in the future.

Carotenoids are the massive group of colour enhancing compounds that are stored and exhibited in a fish. They are a group of chemicals that impart colour by the way they absorb and reflect light. Those that refract higher wavelengths of light (reds)are more desirable than those that refract the lower end of the spectrum (yellow). They are organic in nature, and are very closely related to Vitamin A, and similar in structure to vitamin E. Due to their similarity in chemical structure to these 2 vitamins, they behave in a similar way in living tissue, being very reactive and unstable, easily degraded in oxygen heat and light.

As carotenoids do degenerate over time, in the same way that a leaking bucket needs to be topped up to keep it full, koi require a constant supply of carotenoids to keep the chromatophores packed with carotenoids.

Many different organisms (including shrimp, krill and koi) have the ability to convert certain pigments into others. Shrimp and krill are marine crustacea, and are renowned for their red pigmentation caused by the carotenoid astaxanthin. However, these filter feeding organisms feed on marine algae that is suspended in the water (and definitely not pink!), converting a range of pigments (carotene, lutein, and zeaxanthin) into the red pigment astaxanthin.

Natural sources:

There are several recognised natural sources of carotenoids suitable for colour enhancement. Like any natural commodity, qualities and pigment content can vary from source to source, and being organic, can be liable to degradation during food manufacture. However, natural sources are also renowned for offering a superb range of carotenoids. For example, marigold petals have more than 20 different carotenoids. They also have a high concentration of these compounds (approximately 9000mg per kilo), whereas shrimp or krill meal will only have about 200mg per kilo, with the added issue of the exoskeletal material have an exceedingly high ash content.

Good natural sources of red pigmentation include shrimp, prawn and krill, with similar red pigments found in high quantities in red peppers (paprika).


reference 1: Jason Selong
reference 2: Pond Doctor Answers
 
 


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +9. The time now is 02:09 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright © 2000-2008 Arofanatics.com (Since 30th August 2000)