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FAQs on Aquatic Coloration

Related Articles:  Coloration Pigmentation In Marine Fishes By Mark Evans Aquatic Behavior

Related FAQs:  Aquatic Behavior

melanistic  2/27/12
Melanistic is as expression used to characterize a dark or darker fish.
May be few years ago, someone found the expression "LUTEOMELANISTICS" here, used to refer to a black ocellaris with orange face.
<Am not familiar w/ this term>

Looking for this word, using Google tools, result in NO REFERENCE.
Have you ever heard you read it?
<Have not>
Could you please help me to find if this is a true and correct expression?
Thank you in advance for your time and help.
Mauricio Fóz
<Wish I could tell you more. I have a survey article on WWM concerning fish coloration and behavior, but know no more. Bob Fenner> 

Why are coral reef fish so colourful?
> Guys,
> I was asked this today, but couldn't give a simple answer. There's a not terribly helpful discussion at Straight Dope, and a rather better article at some diving magazine web site. But can any of you tell me what the current thinking is?
> http://boards.straightdope.com/sdmb/showthread.php?t=402272
> http://www.dtmag.com/Stories/Ocean%20Science/08-07-feature.htm
> Are the bright colours of Malawian cichlids on rocky reefs at all comparable?
> Cheers, Neale
<I consider them as such. B>
Re: Why are coral reef fish so colourful? 6/28/10
Hi Bob,
It's surely a bit more complicated than like-for-like though. I just sent this to James in another e-mail, but may be relevant to your thinking, too:
<Ok. B>
"When I was at university I spent some time talking with a researcher on Malawian fish. Among other things he'd established that the bright colours the males had served no function beyond appealing to the females. Unlike reef fish, male cichlids are colourful while females are camouflaged.
Supposedly, the male's colours attract predators, so to reach maturity the male has to have been clever, fast, and healthily free of parasites. So by selecting for the most conspicuously coloured males, the females were choosing the males with the best genes. What was more bizarre was that sometimes the females changed their minds about which colours they preferred, so you'd get blue males of the species in one place, yellow males somewhere else, each reflecting the particular tastes of the females -- which were in turn presumably making choices on which colours were the most "honest" indicators of genetic fitness in a particular part of the lake.
But in coral reef fish, males and females have the bright colours, so this model doesn't really work."
Cheers, Neale

Enhancing the gold colour in Asian Arowana -- 09/03/09
Dear WWM Crew,
I am interested in learning how to enhance the gold colouration in the Asian Arowana, in particular the golden variety. I would appreciate if you could point to relevant literatures in this respect, if any.
Many thanks and best regards
Seow Lim
<Colour in Asian Arowana is largely genetic, and you "get what you pay for". As with any fish though, the best colours depend on environmental factors and a good diet. Most fish should their best colours in a dark
tank, in particular things like a dark substrate (black sand for example) and overhead shade provided by floating plants. A stressed fish won't show its best colours, so you need to ensure an Arowana has plenty of swimming space and excellent water quality. Tankmates, if any, shouldn't be aggressive or nippy. Diet is central, since at least some fish colours can only be produced when the fish eats the right things. In particular, algae and crustaceans seem to be influential. In terms of algae, pellets may work best, either directly, or stuffed inside frozen fish or prawns. For crustaceans, things like *unshelled* shrimps and krill work well. On the other hand, a bad diet will mean an unhealthy fish, so a loss of colour.
Live feeder fish would be the obvious, most foolish way to feed an Arowana since these have a very high risk of introducing parasites. Furthermore, carp family fish (such as Goldfish and Minnows) contain a lot of fat, and there's ample evidence this caused problems in predatory fish. Similarly,
thiaminase is an issue, so you want to restrict foods that contain this substance to once or twice per week. Goldfish and Minnows (and seemingly all carp) contain this stuff, another reason not to use feeder fish. But
numerous seafoods contain it too, including shrimps.
So, in short, you can't add colour to an Arowana beyond what its genes allow, but you can ensure you get the very best colours your fish can have by providing the right habitat and the right diet. Cheers, Neale.>

Re: Enhancing the gold colour in Asian Arowana -- 09/03/09
Dear Neale,
Many thanks for your almost instantaneous reply.
<My pleasure.>
Whilst I recognise that the colour of the Asian Arowana is largely genetic, I was wondering whether the use of certain colour enhancing substance such as astaxanthin would help to bring out the best of the gold colour in the golden Arowana.
<Not substantially. If you could feed an Arowana and make it look like a more expensive one, then that's what people would be doing! Why buy a $5000 Arowana when you can just feed a $50 one and get the same results! While there's plenty of "colour enhancing foods" out there, none of them make a huge difference.>
This usually involves two processes. The first is to reduce the dark colouration on the back of the golden Arowana which I understand is due to the effect of counter shading so that the back colour will be lightened
exposing the shine of the fish.
<Not sure I quite understand this. Fish generally make their backs darker to match a dark substrate. The idea is to become less visible to predators (like birds) above them. Bright lights above them (like the sky) makes them lighten the colours of their bellies, so that they're less visible to predators underneath them (such as bigger fish). Whether or not Arowana do this is debatable, particularly in the case of farmed, artificial forms.>
The second is the attempt to bring out the gold colour of the fish which I understand is done in a number of ways including the use of lights in what some refer to as "tanning" as well as the use of colour enhancing foods or supplements.
<The food supplements specifically mimic the chemicals in crustaceans and algae mentioned earlier, for example carotene. Regular fish foods often lack these chemicals. Colour-enhancing foods have extra amounts of them, so that the fish can produce their best colours. Only specific colours are enhanced; e.g., carotene improves reds. Carotene is found in crustacean shells, hence my suggestion to use whole, unshelled crustaceans. If you're feeding a diet that already includes algae and whole crustaceans,
colour-enhancing foods will have little/no effect.>
I would appreciate if you could share some of your knowledge with us.
<By all means experiment, but don't expect dramatic results. Most of the colour on an Arowana comes from its genes, and to some degree how well these are displayed depends on its environment. A varied diet will enhance those colours, but it won't dramatically change them.>
Many thanks and best regards
<An interesting topic worth discussing. Thanks for writing.>
Seow Lim
<Cheers, Neale.>

Fishes Losing Color (Inadequate Nutrition) -- 01/26/09 Hi Guys, <<Hey Brian>> I have a 330g reef tank fairly well stocked with 70g sump, weekly 50-60g water changes, ozone, skimmer, Kalk reactor, 4 x 400w HQI MH 20k. <<Cool>> I maintain good water quality and stable conditions. I have noticed many of my fish have slightly lost the vibrant color they had when introduced to the tank, mostly: Lyretail anthias (the male and females), purple tang and Sailfin tang. The color is more faded on tangs, and on anthias the appearance of slight darker spots on them. My blue/green chromis, orange clownfish, and Pseudochromis still have very good color. I have been feeding: Bio-Pure mysis shrimp green seaweed <<Ah! This alone is not enough to adequately meet the nutritional requirements of your fishes and is very likely the reason for their loss of color vibrancy. Food additives can help (Selcon/Selco, Vita-Chem), but these often are abused or simply not provided due to the cost/hassle. Offering a wider selection of frozen foods would also be of benefit'¦but if you do nothing else, I VERY MUCH suggest you add New Life Spectrum pellets to your fish's diet. This pelleted food is very palatable and amazingly nutritious and wholesome. I have a 375g reef display housing five Tangs from four genera. Along with an assortment of frozen foods, I provide daily offerings of the Spectrum pellets and the colors of these and all the fishes are (admittedly'¦my opinion) spectacular>> I have recently switched to PE mysis due to higher protein content (although I am starting to wonder if they get higher simply due to less water mixed into cubes) and brown/green/red seaweeds. <<Still not enough>> Rarely do I use Vita-Chem and garlic additives. <<Okay>> I have also recently stopped using carbon due to suspected involvement w/ lateral-line on my tangs. <<Mmm'¦this will also likely be 'cured' with better nutrition>> I am wondering if this is likely a nutritional deficiency or what exactly is the cause? <<Very much an environmental issue'¦and in this case a lack of adequate nutrition, I do believe>> Thanks a lot as always! <<Happy to assist>> Best, Bryan <<Cheers, EricR>>

Re: Fishes Losing Color (Inadequate Nutrition) -- 01/27/09 Thanks a lot! <<Quite welcome Brian>> What's your opinion on plankton cubes, brine, and bloodworms? Worthless and not beneficial? <<The Brine Shrimp is of questionable value, but both the Plankton and Blood Worms are of benefit>> I'll look for those pellets. <<Please do'¦ The Spectrum food will be of great benefit to the health, vigor, and color of your fishes>> Should I continue Vita-Chem and add Selcon also? <<These can also be of benefit (the Selcon more so than the Vita-Chem, in my opinion). I use both on an infrequent basis>> I always had read brine is useless except to entice feeding initially. <<Depends'¦ Adult Brine Shrimp are mostly water with little nutritional value, but if 'gut loaded' before feeding if live, or freezing by the food manufacturer, they can be of some value. Even so, I don't think they should ever be the primary food source. Regards, EricR>>

R2: Fishes Losing Color (Inadequate Nutrition) - 01/27/09 BTW I failed to mention I feed a mix of Formula One, Two, and Reef Blend w/ an automatic feeder 4 times a day. Does this change anything? <<Mmm, no'¦ Our previous discussion on the color and condition of your fishes would seem to indicate it is still not enough/is not 'doing the job.' Make sure the fish are eating this offering'¦and that you are providing 'enough' of it. And I can't mention this enough, but if this were me, I would replace these with New Life Spectrum pellets in the auto-feeder. Cheers, EricR>>

Fish Coloration, and stress, Chromis   - 7/24/08 Hey crew Good day to you all, I hope all is well. <Hello! The same to you!> I have a quick question that I looked and looked on the site for the answer but had no luck. I may be looking in the wrong place, but I thought I would ask anyway. <Okay> So I have a little green chromis that shares a 60gal with two big chromis. Well, the little guy has always had a blotchy or spotty looking coloration but his behavior seems normal. When I put the first chromis in the tank to help cycle the tank he also appeared like this as well, but shortly grew out of it. My question is what causes this coloration? He does get picked on by the other two a little, but nothing that keeps him from strutting around the tank and eating everything I put in. I read the articles about why and how fish change color and the various types (cited here: http://www.wetwebmedia.com/AqSciSubWebIndex/coloration.htm). Well, the concern I really have is more related to my Kole Tang that has been in the tank for about three weeks now and doing great. <Needs more space...> Although, this morning, I turned the lights on earlier then usual, and his coloration looked blotchy and spotty like the chromis. I immediately put a pinch of pellet food in and he gobbled it up. I took a shower and got ready for work and went and checked on him (about 20 minutes overall). He was fine. Color back to normal and active as usual. I took two samples of my water today to check at my LFS on my lunch. I figure maybe I have a water quality issue, so I will have it checked and do a water change tonight (which I regularly do every other week). Now I have never noticed this before on him, although, he is a bit skittish still. He is the man of the tank. The other fish leave him alone and somewhat "run" the other way when he comes around except for the maroon, they seem to have become friends. I did introduce two new fish to the tank a few days ago. They were a Orchid Dottyback and a Lawnmower Blenny. <Quarantined?> I do know that the Orchids can be a touch ornery, but I have yet to see him since he was added. Could he be causing stress to the tang for a change of coloration? Well I hope this was enough information. Thanks for your time and constant attention to helping people like me. <I'd say this is most likely stress due to crowding or water quality issues- do see about a larger home for that tang, as well as quarantining new arrivals for 4-6 weeks. Water changes and the works as well, varied feeding...general stress most likely the culprit here.> Spencer <Benjamin>

Re: Fish Coloration - 7/24/08 -- 7/30/08 Am I over crowded due to the amount of fish in the tank? <Not really, more just a little cramped for a fish that swims in long spurts> I read on wet web that they need a 50-60 gal tank. So who should I get rid of to make him happier? <He's probably not miserable, although this isn't ideal...I think it's a good excuse to keep in the pocket for a tank upgrade later on...> He shares his tank with three blue chromis, 1 Dottyback, 1 lawnmower, and 1 maroon. All of those fish are relatively small. Also, if I start to use Selcon will that help his immune system overall, that it may help this problem? <Sure couldn't hurt. Better nutrition can help with stress and coloring problems> I did do a 3 week quarantine with those two new additions, they were also at the LFS for about 2 months before I purchased them. <Glad to hear it...good job> I am nervous about this because I am taking a three week vacation out to LA and don't want anything bad to happen. <I don't think this sort of chronic trouble will cause trouble of an acute sort so soon...but do see about amending nutrition, water quality. Also check to make sure none of these fish are harassing each the other.> Thanks for your help. Spencer <No problem! Benjamin>

Re: carotenoids and seahorses    5/16/07 Dear Bob: <Pete!> So that's what gives the Garibaldi their brilliant coloration -- those dazzlers really stand out in a kelp forest like neon signs! <Ah, yes... am particularly fascinated by the more-shallow water juveniles with their brilliant blue highlights> That's a  fascinating subject (certainly the habitual sponge eaters are among the most  vividly colored of all the marine fish). <Yes... had a few conversations with friend and fish-food maker Chris Turk years back... trying to convince him to investigate, incorporate such material/s in his frozen fish food prep.s... With some success. Always strikes me as strange that folks don't consider/realize that with so much of a given material present (e.g. live coral polyps) that there should not be predators about...> No one has done a similar study  specific to seahorses to my knowledge.  The Vibrance enrichment formulas  developed for Ocean Rider specifically to meet the long-term nutritional  requirements of seahorses include pure  Astaxanthin and other carotenoids as key ingredients, no doubt based largely on  information from papers such as yours.  I would like to read your Garibaldi  paper sometime if it's available. <Can, will look through my old files if you'd like... Not keyed/computerized, so if you'll send a FAX number along...> Best  of luck with all of your projects, sir! Respectfully, Pete  Giwojna <And you and yours my friend. Life to you. Bob Fenner>

Hi Everyone, Attached is a paper about mimicry in coral reef fish.   10/29/06 I would especially like to thank Erik Schlogl and Bob Fenner for allowing me to use their photographs. Best Regards Ashley Frisch James Cook University. Dear Author PDF offprints Blackwell Publishing is pleased to advise you that a PDF file of your paper is attached to this email. Please note that this replaces the procedure of sending free offprints by post. If you have any queries please contact the Production Editor at: mae@oxon.blackwellpublishing.com PDF Terms & Conditions Please note the following Terms and Conditions regarding the use of the attached PDF file of your Article. Use of this PDF file indicates consent to these Terms and Conditions. Provided that you give appropriate acknowledgement to the Journal and Blackwell Publishing, and give full bibliographic reference for the Article, and as long as you do not sell or reproduce the Article or any part of it for commercial purposes (i.e. for monetary gain on your own account or on that of a third party, or for indirect financial gain by a commercial entity) you may use the PDF, in the following ways: o        you may share print or electronic copies of the Article with colleagues; o        you may use all or part of the Article and abstract, without revision or modification, in personal compilations or other publications of your own work; o        you may use the Article within your employer's institution or company for educational or research purposes, including use in course packs. Please note that you are not permitted to post the Blackwell Publishing PDF version of the Article online. Self-archiving of author manuscripts .         Submitted version: You may post the original manuscript of the Article, as submitted for publication in the Journal, on your own personal website, on your employer's website/repository and on free public servers in your subject area. We ask that as part of the publishing process you give appropriate acknowledgement to the Journal and Blackwell Publishing. You agree not to sell or reproduce the Article or any part of it for commercial purposes (i.e. for monetary gain on your own account or on that of a third party, or for indirect financial gain by a commercial entity). .         Accepted version: Twelve months after publication you may post the original manuscript of the Article, as originally submitted for publication in the Journal, and updated to include any amendments made after peer review, on your own personal website, on your employer's website/repository and on free public servers in your subject area. Appropriate acknowledgement to the Journal and Blackwell Publishing, and full bibliographic reference for the Article must be given. In addition you agree not to sell or reproduce the Article or any part of it for commercial purposes (i.e. for monetary gain on your own account or on that of a third party, or for indirect financial gain by a commercial entity). The electronic version must include a link to the published version of the Article together with the following text: 'The definitive version is available at www.blackwell-synergy.com <http://www.blackwell-synergy.com/> ' For additional information regarding any use of this PDF file not covered by these Terms and Conditions, please refer to the Blackwell Rights Department at: journalsrights@oxon.blackwellpublishing.com. Use of this PDF file indicates consent to these terms and conditions. mae_103.pdf (Binary attachment) The Physiology and Behavior of Color in Fishes information  7/5/06 Dear sir: I am interested in the article : The Physiology and Behavior of Color in Fishes, but it seems no author's information. Could you tell me ? <I am the author of this survey piece... It is quite old. Bob Fenner> Sincerely, Cheng Bang Chu

Re: Goldfish turns yellow!  - 03/22/06 Dear Bob, <Teti> Thank you for your e-mail. I'm glad to hear that there is nothing wrong with the fish. Could you explain though why this is happening? <Mmm, maybe... Turns out, the mechanism/s that determine color and reflection in Goldfish breeds are not "well fixed"... and that some are becoming more random w/ lack of detail by breeders. Due to whatever influences... water quality, nutrition mostly, along with genetic (pre)disposition, some do change color... mainly "reverting" back to browns of sorts (their "natural color"), but some white, some even mottled/mosaics... Makes sense teleologically that there should be such "drift", as there is demonstrated survival value (being able to avoid predation by "blending in")...> I visited the link you sent me and we will try to enrich the diet of the goldfish. We've started feeding them blanched courgettes and spinach. <Ah, good> Once again, Thank you! Teti <Welcome. Bob Fenner

Color change  12/21/05 From the references in your excellent web pages on color in fishes, can you tell me what the letters "TFH" and "FAMA" stand for? I'd like to look up these references. <Richard, they are magazines.  Tropical Fish Hobbyist and Freshwater and Marine Aquarium.> Thanks, <You're welcome.  James Gasta Richard Ellis <<... THE R. Ellis? RMF>> Ultrafluorescent  9/7/05 Hi friends: We live in Baja Sur, Mexico... so far on the ocean at night, and not always there are special things that shines very brightly, specially related with the movement...nobody here knows the name of this parasites, fish, who knows.... They are supposed to shine more on bays, near the rocks or at the shore, but even if you inside the ocean they are by tons, they leave like a wave of glitter....so nice, so peaceful... By any chance, do you know the name of these things? We would appreciate your help Regards Hugo and Josefina <There are many phosphorescent organisms in the sea... some are indeed spectacular... the most common in Baja are largely algae that "sparkle" when disturbed by surface activity. Bob Fenner> The Ethics of Glo-Fish (TM) (6/5/05) Hiya Bob, <<Howdy. RMF>> I just finished reading the article on the Glo-fish, and I was wondering if it would be possible to ask the author if he considers every breed of dog, most breeds of milk and beef producing cattle, and probably 80% or better of all of the grains and fruits he eats as also being 'garbage' due to the fact that they are also man induced 'mutations' (yes, the method may be different, but the intent and process is the same and similar-one is just more 'trial and error, after all, no?) For the record, I also don't like the idea of Glo-fish, or painted chandas, but plenty of folks hate telescopes, black moors, fancy guppies and swords for just as legitimate reasons. <Agreed> I can understand a POV of distaste and dislike, I was just wondering what selective bias the author uses to determine which of our obvious genetic alterations are 'garbage' and why? ;) (heh, maybe I should write a counter point article for submission, playing devil's advocate) <All submissions are welcome for consideration. You will have to use a lot better grammar than you did in this e-mail. Please capitalize the proper noun "I" and the first letter of sentences. We post all e-mails and replies. It's a lot easier for folks to read them if they are punctuated properly. If you do it then we can spend less time proofreading and more time answering.> Keep up the good work-been observing your website for years, all the best! Alan <Thanks. The author of the article is not a member of the question-answering crew, so I do not know how to contact him. I do agree with you on this issue. I have nothing against Glo-Fish (TM) myself. They were created to serve a utilitarian purpose (pollution detection). If there is a side benefit of providing pretty fishes that have not been chemically burned and dyed, that's great from my perspective. I have no problem with GM foods either. I say you're right that there is no difference in principle between this and selective breeding. It's only method and speed. In fact, GM is better because the planning will lead to fewer bad mutations. It just needs to be properly regulated. As for the other fish you mention, I have qualms about some of them. If fish are selectively bred for appearance, I only have a problem if that creates a deformity that impairs the fish or causes pain. Some of the fish sold these days definitely suffer as a result of their selectively-bred appearance. That's my opinion, for what it's worth. Steve Allen>

Question: behavior of color Dear Dr. Fenner, <Just Bob please, I have no doctorate> I enjoyed reading your article on The Physiology and Behavior of Color in Fishes. I am writing a children's book on albino animals.  I am trying to understand leucism, which according to my research is defined as white or weak coloration. What causes leucism?  Is it due to less pigment, less or abnormal chromatophores, or by the movement of pigment to different layers of the epidermis? <Is of genetic disposition. A partial expression of color... imagine a multi-gene trait with only part passed on to offspring... and conditions allowing the presences of said young (most are eaten due to lightness of color by predators)> Thank you for your time.  I appreciate your help and will give you credit in my book. Sincerely, Randi <Thank you my friend. Bob Fenner>

Re: question: behavior of color Hi Bob,      Thank you for writing. So, would I be correct in saying:  "In leucism, melanocytes function abnormally.  Although the vast majority of melanocytes is defective, many leucistic animals have certain areas of normal coloration, as in their eyes or on their faces."   Again, thank you for your help. Randi <Actually, no... the actual color cells that are present do function normally... but through inheritance, leucistic animals have partial to complete (even non bilateral) absence of said melanocytes. Bob Fenner>

Re: question: behavior of color 12/25/04 Now I'm beginning to understand leucism better, so that I can explain it to children. Is it correct to say: Through inheritance, leucistic animals have partial to complete absence of melanocytes. <Umm, not absence... this is albinism> Although there is a reduced number of melanocytes, many leucistic animals can make some melanin in certain areas, as in their eyes or on their faces. <Yes> I would like to credit you in my book.  Do you have a degree that I can add to your name? <Not necessary, Bob Fenner>

Color Vision in Fishes Hi gang, The question just occurred to me as to whether fish in general and Tangs of various varieties in particular are color blind. Nothing shows in your data base. So, to your knowledge has anyone tested for this? Regards, Charlie H. >>>Hi Charlie, Yes, fish are equipped with both rods and cones, and can see color very well. Some deep water fish can only see in reds and greens - tangs, being surface fish can detect the entire range. Jim<<< Regarding Melanophores! Hi there Dr. Fenner, <Just Bob, or Robert if you must> I emailed you once before about a month ago. In your paper on the Wetwebmedia website, do you know where you found the information on acetylcholine and epinephrine and its effects on the melanophores? <Would have to search through the posted references... it's been a great while since I reviewed the root information> Please email me back and help me! Sincerely, Nicole <Are you able to search the literature... at a large (college) library? Bob Fenner> 

The Physiology and Behavior of Color in Fishes Dear Dr. Fenner,     I really enjoyed this piece and would like to give proper credit to you. Can you please email me the proper citation for this piece? Thanking you in advance! Sincerely, Nicole Hitchen <Fenner, Bob. 2004. The physiology and behavior of color in fishes. Tropical Fish Hobbyist Magazine, Sept. 2004.>

The Physiology and Behavior of Color in Fishes  Dear Mr. Fenner,  <Ms. Palmer>  I read your excellent article online at WetWebMedia and found it very informative- I would like to cite your work in a report I am doing on Zebrafish coloration and give you proper credit, but I am missing some key bits of information. Could you perhaps tell me when you wrote or posted the article, and if it was ever published in a non-internet source (and if so what that source might be)?  <This small survey piece was written and posted just this last year... and did run in Tropical Fish Hobbyist Magazine... about six months back. Am out in HI or I'd look up the citation for you. Perhaps you can just cite WWM as the source with myself as the writer>  I hate to impose but I would really like to give you the proper credit for this piece, it definitely helped me with my paper. Thank you very much for your time.  Sincerely,  Adriana Palmer  Brown University, '05  <Please make it known if I may be of other assistance. Will be back "home" in a week or so. Bob Fenner>

Fish Coloration - Why? Dear Web Media, Why do freshwater fish have dull dark backs and shiny silver bellies?  I am home schooled and have not been able to find the answer to this question. Thank you.  From,  Jena Ritchey. <Well, Jena, there are some very good reasons for this kind of coloration on fishes.  The silvery belly, when seen from below, blends in pretty well with the light color of the sky as seen from underwater, so predator fish might miss out on seeing their prey, or so the prey fish might miss out on seeing the predator sneaking up for a snack.  The dark color is harder to see from above, like from a fish-eating bird looking down, so the dark color will blend in with the mud, sticks, and such underwater.  Not all fish are colored like this, though; in fact, there are a few fish that are colored quite the opposite - with dark bellies and light backs - and swim upside down!  Most fish will turn very very pale at night, when it's too dark to see and their dark color isn't very useful.  There are also a lot of very brightly colored freshwater fishes in nature.  Some of these fishes come from muddy, cloudy waters, and are brilliantly colored so they can see each other and find mates; in these mucky waters, it's not as important to have the dark on top/light on bottom colors, because they wouldn't be very useful; if their predators can't see through the water very well to begin with, there's no reason to try to blend in, right?  Here's a link to a picture of one of many such brightly colored freshwater fishes:  http://www.fishbase.org/Photos/PicturesSummary.cfm?ID=53747&what=species Hope this sheds some light on things for you!  -Sabrina>

Question re behaviour Dear Crew <David> This is probably a most fundamental question from a novice, and yet to date I have not heard a reasonable (informed!) answer to it:- Q.  Why have certain genera of fish swim evolved to swim with a tail-down attitude - e.g. Nannobrycon and Thayeria and for that matter why do some swim with a nose-down attitude - e.g. Abramites?  The thought is that it is linked to feeding habits and yet it would seem to disadvantage such fish {compared to those that swim 'horizontally'}  should they require to escape rapidly from predators. Yours sincerely Brian <Have not seen much (anything re spatial orientation function) and these Characoids (or other fishes for that matter) either. Will make some speculations. The parts of the world (Amazon et al. basins in South America) where these animals are found are relatively "old" and crowded relatively... and so as general rules go, there is more competition for food, space, avoidance of predators... Perhaps the "abnormal" positioning in the water column confers a benefit in not appearing like a food item? Maybe there is something to being able to escape up/down instead of ahead, to the right, left in avoiding "arrow shot" attacks by predators? Maybe something/s re these "tetras" markings, coloration and change therein matches with plant life, particle movement, light propagation... in their environment? Maybe it's time for you and I to make a trip to Brazil's outback? Bob Fenner>

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