I've recently worked with salmon and had the same problem (or similar). I was told to feed them more as it was due to malnutrition. That seemed to help. Do they have any parasites at all? Salmon lice remove scales and are pretty obvious, but I don't know much about trout. I imagine antibiotics wouldn't kill external parasites, though so it might explain your problem if it's not about nutrition.

In my experience , not with trout but with other types of fish, lack of nutrients, and exposure of toxicants especially pesticides caused quick scale loss. Both reasons contributed equally.

When Atlantic salmon (Salmo salar L.) goes through their smoltification period, the scales become very loose, and one should be careful with any handling. In my mind, this is a natural response to the hormonal shifts that occur during smoltification where a series of hormones interact (growth hormone, prolactin etc.). Maybe you are working with strains that has an anadromous character.

In my experience with freshwater species (carp and tropical fish) and with seabass and seabream, the scales lossing is more related to protozoan parasites. In extreme cases I've used formaldehyde 37% at 4 ppm, but it depends on the species because it is very strong and toxic, also I was working at small scale and for use in lab, not for further comsuption. However, I found this site very useful http://content.cdlib.org/view?docId=kt438n99wc;NAAN=13030&doc.view=frames&chunk.id=d0e2305&toc.id=0&brand=calisphere, maybe there is information that you can use.

Most of the problems with the scales loss are related with handling and nutrition, and shoul be resolve with high level of minerals in the diets, mainly zinc. I hope this can help you

In most cases, its nutritional problem

Thanks to all replies,

It is not due to the parasites for sure.

It could be persiticieds. However, if so it should at least show seasonality. Or seasonally the level of scale loss should fluctuate.

I also suspect that it is due to the nutrition knowing to the fact that it is a chronic problem. Especially during summers up to 25 C, very little feeding is done. If feed has less of something, I guess shortage becomes unbearable.

So far, from the replies, zinc comes out as a lack of trace elements, Ca

was suggested as another.

Suspecting the nutriiton, we had doubled the level of premix, it also had zinc and all the other trace elements in it. I have also access to the same size fish in three other farms. Feeding activity of fish significantly changed.

Zinc, I really like it, (usefull for learning diabilities and hair fall of in humans:-) ), but I usually avoided for overloadings of zinc for the fact that it increases routine metabolic rate. That is, when iddling time is increased, body actually aquires more nutrition of other types.

Anyhow, I will do a couple of experiments in my labratory and see what happens..

Hamdi

Well John, telling people to Google the answer is not really an answer, especially as most of us know about the internet.

Hi Hamdi. First I'm curious about the species of trout you're working with? If it's rainbow and they're being exposed to temperatures as high as 25 C, this must be very close to their physiological tolerance limits. Are you seeing mortalities as well?

As Björn Olav correctly pointed out, Atlantic salmon become very susceptible to scale loss during the smoltification process (I'm not sure if we know why, perhaps it's related to the silvering process), but this is a transitory situation, and as the fish move into seawater as postsmolts, this problem disappears.

When you ask about scale loss, I'm also curious if you actually see lost scales on the bottom of the tank (as we might see during salmon smoltification) or is you're seeing "disappearance" of scales. I ask this because scale loss and scale resorption are two completely different processes. Scale resorption can occur through osteoclastic activity, usually during periods of increased calcium demand by the fish during which calcium from scales may be resorbed, and thus the scales themselves. One of my students, Petra Persson, studied this process in relation to sexual maturation and nutritional status, and I'm attaching one of her several papers below.

Article Estradiol-17?? and nutritional status affect calcium balance...

In my personal experience, the Carp fish (fingerling size) were loss their scales as a patchy pattern (mostly in peduncle-lateral region) when starved for two continuous weeks. It seems the malnutrition causes this problem. Anyway, using supplementation, including cholecalciferol, amino acids and minerals (P, Ca, Mg and Zn) for a long period will restore your fish (balanced diet).

In addition, some fungal infections like Fusarium Sp. can provide dermal problem, including scale loss.

When the water temperature increases, the scale oedema and then sloughing of that can be seen in salmonid fish as a result of Aeromonads septicemia. Scale missing can be occurred following some bacterial infections: Rhodococcus, Mycobacterium, Moraxella, Vibrio and Winter Strawberry Disease with undefined bacterial agent(s).

The water hardness should be checked, soft water may provide same issue due to lack of Ca & Mg concentrations in water (the main route for +2 ions uptake is water and gills).

Overcrowding and handling could resulted that, please treat them with salt bath.

Did you observe any skeletal deformation as well?

Hi Bjorn,

It is rainbow trout. We sometime get to 26 C, but do not see any mortalities due to the temperature I should say. However, feeding is minimized, or sometimes stopped for 5 days. Not that they would not take the feed, but the cost of feeding is more than what is getting through feed.

Nutrition is one issue really. Due to the reduced feeding zinc deficiency may be kicked in leading to scale loss. However, at the beginning of the summer just the end of active feeding the level of scale loss is also considerable high.

Scale loss is the most evident during feeding.

Rainbow trout is kept in damp/lakes.

...

You apparently have quite a heat tolerant strain of rainbow, as most studies report critical tolerance limits for rainbow trout to be 24-26 C. Although the fish may be able to survive, the near-lethal temperatures have extremely negative impact on the physiology of the fish. Thus, metabolism is very high while the appetite is low. At the same time, the temperature elicits various stress responses. Together, my guess is that the fish are in a catabolic state under these conditions. Although I can't tell you why exactly the trout are losing their scales, I don't find it surprising due to the generally adverse effect of the high temperature on physiology. I'm impressed that the fish survive at all!

Dear Hamdi

I agree with Björn Thrandur Björnsson,

Apart from what he has explained, I see a probable cause of Vit E diffeciency if no parasite is involved... as U didnt get any positive response to antibiotics, the bacterial role is ruled out.Otherwise Look in to what Björn Thrandur Björnsson has suggested,

Good luck

azad

good morning researchers

i am working in brackishwater fishes..where in Mullet we found the scale loss whenever we handle the fish..our scientists say that is due to stress.. in many case which will lead to mortality.. i read one article which say magnesium ion concentration in the body fluid plays a role in scale loss..I am not remembering exactly the journal name.sorry friends.

As of today, the second rearing season,

1) It seems scale loss is not at alarming rates (adds more confusion). Feed, or more importantly antibiotic change could be responsible for this shift, even strain of fish (?) or some sort of unnoticed pollution.

2) Stress is another issue, but its solution is usually easy with vitamin C for three days 2.5% of feed (I use 1/3 of daily feed amount for vitamin addition) for 2-3 days. It uplifts fish pretty well.

I am still inclined to belive that scale loss is due to various reasons, sometimes bacteria, sometimes because of handling sometimes due to lack of say magnesium while sometimes it is due to lack of something zinc or a related trace element.

A holistic approach is needed to decrease its impact. It is also interesting that we got the lowest returns in the last year. That is, fish did not grow as it did before or this year. There was something really wrong. This year everything looks good. No significant scale loss, minimal occurring is due to the bacteria. After antibiotics it seems it goes away.

May be density of fish in your acuariums is too high?

I have not yet encountered this problem of scale loss in rainbow trout. But, considering the problem, I agree with Prof. Björn Thrandur Björnsson suggestion. My best guess is to check your stocking, In general, if water temperature becomes high in association with higher density of trout causes unexpected severe problems. It is good to learn they survives. Please also check the water quality.

Dear Hamdi,

Regarding to your question I found valued article with title as follows:

Effect of a Partial Loss of Scales and Mucous on Carbohydrate Metabolism in Rainbow Trout (Salmo gairdneri.

You can see mentioned site as follows:

http://www.nrcresearchpress.com/doi/abs/10.1139/f67-084?journalCode=jfrbc

Unfortunately, just abstract was availabe. If any body find full text please reply me.

Kindly regards

Jalil

Have you checked viral causes? Lymphocystis is a viral disease that begins with scale lifting. See this article:

Immune Efficacy of a Genetically Engineered Vaccine against Lymphocystis Disease Virus: Analysis of Different Immunization Strategies

Fengrong Zheng, 1 Xiuqin Sun, 1 ,* Xing'an Wu, 2 ,* Hongzhan Liu, 3 Jiye Li, 1 Suqi Wu, 2 and Jinxing Zhang 2

Evid Based Complement Alternat Med. 2011; 2011: 729216.

Published online 2011 July 19. doi: 10.1155/2011/729216

PMCID: PMC3140788

Dear Jalil,

Thank you for the info. I checked the paper but could not have it yet, I will certainly send it when ever I get it. Be aware that in that paper they removed the skin and observed fish. But it is a good point to study.

Dear Garry,

We routinly screen for IPNV, but never had any sign of Lymphocyctis. We are familiar with the disease in sea bream.

Widely fluctuating oxygen levels may be stressful enough to cause scale loss. If this were the case you might also expect to see increased bacterial and fungal infections over time. The oxygen level would not need to drop so low for a sustained period that would result in mortality, just low enough for short periods to induce stress.

Hi Henry,

it is an interesting point. This is an artificial dam case, but physiochemically now it looks like a lake. Oxygen fluctuates by photosythesis and feeding. It used to be only feeding which leads to the fluctuation is the O2. But now phytoplankton seems to be an important factor. As a response now I suggest to finish the last feeding at least 2,5 hrs before sunset.

On the other hand decreased O2 also means less efficient digestion. Too much plant based (which also has carbohydrates) diet could also be increasing efficient digestion time. This is also what I believe and try to manage in trout culture here.

I've found scale loss in the omnivore chelon labrusus doe to the diet composition. Excess of protein or glucides in the diet cause fatty acids production, which replaces the water accumulated with the protein deposition,lipids don't make any contribution to the weight growth. You can find it out checking the activity of the glucose 6 phosphate deshidrogenase ( G6PD) implicated in yhe pentose phosphate pathway. If its high the fish metabolism is deviated into fatty acids sintesis instead of growing

Dear Maria, thank you for your response, it is very good point.

Dear Hamdi,

What about your opinion about some fungal and bacterial disease in mentioned disorder?

Please pay attention to Furunculosis and Saprolegniasis in Rainbow trout and their pathogenicity.

Regards

Dear Jalil, we tend to think systemic bacterial infections. However, skin diseases of fish is ignored often. Those are mostly problem, but they are only problem when fish is weakened by mainly by diet, or some other factors.

Fortunately we do not have A. salmonicida here, and we have fungus saprolegnia in juveniles smaller than 3 g (fungus is mainly problem in colder problems). We can easily control it by disinfection. If I see fungus, disinfection is a must but it is an indicator of diminished immunity. That is why my first response is to use pulsed vitamin C in feed up to three percent.

We have lactococcus and streptococcus in the system. poorer kept fish will probably will get exposed to the cycles of infection in the early summer.