Here's the paper I was originally referencing. I was 100% wrong. It isn't on JSTOR, but was published in Aquaculture.http://www.sciencedirect.com/science/article/pii/S0044848697001336
No More BS About BS!
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This will make it easier for the rest of the community to see that there is indeed evidence that fish can digest chitin. The pertinent statement is in bold type.[h=2]Abstract[/h]A study was designed to determine the presence of chitinolytic enzymes in cobia. Additionally, the source of the chitinolytic enzymes (bacterial or endogenous) and apparent digestibility of chitinous waste meals were investigated to determine the viability of crustacean processing waste products in juvenile cobia diets. Antibiotics were used to eliminate potential chitinolytic gut flora and chitinolytic enzyme levels were compared to control fish fed an identical diet without antibiotic. Chitinase and chitobiase were measured in the stomach, pyloric caeca, and anterior intestine but were only detected in the stomach. Control stomach chitinase and chitobiase activities were 3075 ± 709 (mean ± SD) and 2076 ± 208 μg N-acetylglucosamine (NAG) g[SUP]−[/SUP][SUP]1[/SUP] h[SUP]−[/SUP][SUP]1[/SUP], respectively, and not significantly different from antibiotic treatments. This suggests substantial endogenous production and that the activity, if any, from chitinolytic bacteria is not significant. Additionally, high chitobiase levels indicate breakdown of chitin to potentially nutritive NAG. To determine the apparent digestibility coefficient (ADC) of shrimp processing waste meal (shrimp meal) and crab processing waste meal (crab meal) in vivo, diets containing a 70:30 mixture of a reference diet and test ingredient with the inclusion of the non-digestible marker yttrium oxide were fed. Chitin ADC for both crab (mean = 66.8 ± 4.5% SD) and shrimp (78.2 ± 8.0%) meal was high and not significantly different. Organic matter digestion was significantly higher in crab meal than either shrimp meal or the reference diet. However, crude protein, lipid, and gross energy digestion for crab and shrimp meal were not significantly different from the reference diet. Both enzymatic and in vivo results indicate the capability for juvenile cobia to digest chitin through strong endogenous chitinolytic enzymes. The addition of crustacean processing wastes in cobia diets has the potential to reduce the cost of feed production and increase the sustainability of cobia aquaculture by reducing inclusion rates of fish meal and other more expensive ingredients.
For those not familiar with the term, "endogenous" means the fish produces the enzyme itself, without the help of bacteria in their gut, such as termites and ruminants use to digest cellulose, which is the plant worlds analog of chitin.
For those not familiar with the term, "endogenous" means the fish produces the enzyme itself, without the help of bacteria in their gut, such as termites and ruminants use to digest cellulose, which is the plant worlds analog of chitin.
I took it upon myself to contact Dr Toonen today. He agrees that there are fish which can utilize chitin, but isn't ready to grant that any of the commonly kept marine species can do so without specific studies, which I can understand for someone in his position. I allowed that there is research which shows negative effects, but that the species which show them are largely to primarily herbivorous, to which he agreed. He grants a reasonable chance that other species of a more carnivorous bent might well be found to be able to uitilize it. And he stated that he thought his use of the term "nutritionally void" might have been "sloppy". Essentially he backed up as far as he had to without throwing his baby out with the bathwater. If anyone is still interested at this point I can post the actual exchange with his permission.
Look who's talking! Haven't you learned how badly you come off when our exchanges turn nasty?
I said I would post anything I received and I did. Mot my words about what he said, but his.
Is there a reason why you can not post the complete text of his reply so that anybody here can see it? I am sure he would not object.
Is there a reason why you can not post the complete text of his reply so that anybody here can see it? I am sure he would not object.
Hi John,
Thanks for passing those along. I had forgotten about the Cobia paper in my response to Chris - you are correct, that is clearly evidence that at least some fish produce a suite of enzymes that appear capable of breaking down chitin into a nutritionally useful form. However, it remains unclear how common that finding is, or whether coral reef fishes (which are very distantly related to members of this family which includes cobia & remoras) have any similar ability. I have seen nothing similar for pomacentrids, pomacanthids, acanthurids, or the like that are typically kept in fish tanks. It is certainly not the case that all fish have this ability, because other studies have shown decreased growth (e.g., http://www.sciencedirect.com/science/article/pii/S0044848699001775) or conflicting results among species (e.g., http://epubs.icar.org.in/ojs-2.3.1-2/index.php/IJF/article/viewFile/6836/2584) regarding the inclusion of chitin in the diet. Some studies attribute positive effects of chitin to dietary fiber, some negative effects to decrease of digestability of the meal and such, but few actually test why it happens. Still, most of the research community seem to agree that fish typically do not possess the suite of enzymes necessary to turn chitin into a nutritionally useful form - which is why the presence of those compounds in cobia merited that recent publication.
I agree the results of the second paper are clear, but it actually mentions chitin only once in the entire text (I just checked) and it lists chitin simply as one of the potential differences in the diet composition (it falls into the "some studies attribute effects without testing them" category above). The other differences they mention include a variety of highly unsaturated fatty acids, sterols and the pigment astaxanthin which have each been shown repeatedly to increase growth and survival of captive fishes, and those other substances are exactly what I recommended in my article to enrich the Artemia in order to increase their nutritional value.
I explained why I made the statement that Artemia are not particularly nutritious in my response to Chris (I am assuming he posted it or passed it along to you - if not let me know). So, it may have been sloppy to say simply that they were "devoid of nutrition," but even for Cobia, I would argue that they are the human equivalent of popcorn or potato chips - it tastes good and you like to eat it, but it does not provide a long-term balanced diet to feed a captive fish species. In that first article, they are talking about cutting costs for fish culture by using crustacean fishery wastes (the shells) to supplement fish foods, but the reason they tested it is because that has highly variable results in the literature. The authors provide a cost-cutting measure including the chitinous waste, but still talk about the need for a balanced diet and the shell waste is only one component of the formulated feed. I know of no public or private aquarium in the country who use Artemia as a major feed for any captive fish, and I think that is evidence in itself...
Hope that helps,
Aloha,
Rob
Thanks for passing those along. I had forgotten about the Cobia paper in my response to Chris - you are correct, that is clearly evidence that at least some fish produce a suite of enzymes that appear capable of breaking down chitin into a nutritionally useful form. However, it remains unclear how common that finding is, or whether coral reef fishes (which are very distantly related to members of this family which includes cobia & remoras) have any similar ability. I have seen nothing similar for pomacentrids, pomacanthids, acanthurids, or the like that are typically kept in fish tanks. It is certainly not the case that all fish have this ability, because other studies have shown decreased growth (e.g., http://www.sciencedirect.com/science/article/pii/S0044848699001775) or conflicting results among species (e.g., http://epubs.icar.org.in/ojs-2.3.1-2/index.php/IJF/article/viewFile/6836/2584) regarding the inclusion of chitin in the diet. Some studies attribute positive effects of chitin to dietary fiber, some negative effects to decrease of digestability of the meal and such, but few actually test why it happens. Still, most of the research community seem to agree that fish typically do not possess the suite of enzymes necessary to turn chitin into a nutritionally useful form - which is why the presence of those compounds in cobia merited that recent publication.
I agree the results of the second paper are clear, but it actually mentions chitin only once in the entire text (I just checked) and it lists chitin simply as one of the potential differences in the diet composition (it falls into the "some studies attribute effects without testing them" category above). The other differences they mention include a variety of highly unsaturated fatty acids, sterols and the pigment astaxanthin which have each been shown repeatedly to increase growth and survival of captive fishes, and those other substances are exactly what I recommended in my article to enrich the Artemia in order to increase their nutritional value.
I explained why I made the statement that Artemia are not particularly nutritious in my response to Chris (I am assuming he posted it or passed it along to you - if not let me know). So, it may have been sloppy to say simply that they were "devoid of nutrition," but even for Cobia, I would argue that they are the human equivalent of popcorn or potato chips - it tastes good and you like to eat it, but it does not provide a long-term balanced diet to feed a captive fish species. In that first article, they are talking about cutting costs for fish culture by using crustacean fishery wastes (the shells) to supplement fish foods, but the reason they tested it is because that has highly variable results in the literature. The authors provide a cost-cutting measure including the chitinous waste, but still talk about the need for a balanced diet and the shell waste is only one component of the formulated feed. I know of no public or private aquarium in the country who use Artemia as a major feed for any captive fish, and I think that is evidence in itself...
Hope that helps,
Aloha,
Rob
To which I replied:
> I haven't had a chance to peruse the links you provided, but my own limited reading has shown the species which show negative effects are species which are largely herbivorous.
> To which he replied:That could well be, John. The variable study I linked below includes a trout and a cyprinid, with the cyprinid showing no benefit of chitin enrichment, which matches that pattern. I can imagine that addition of dietary fiber is largely irrelevant for a species with a lot of cellulose, whereas it would be far more likely to be beneficial for a species that is primarily carnivorous... Even given that, I think the popcorn analogy fits pretty well also.
Aloha,
Rob
> I haven't had a chance to peruse the links you provided, but my own limited reading has shown the species which show negative effects are species which are largely herbivorous.
> To which he replied:That could well be, John. The variable study I linked below includes a trout and a cyprinid, with the cyprinid showing no benefit of chitin enrichment, which matches that pattern. I can imagine that addition of dietary fiber is largely irrelevant for a species with a lot of cellulose, whereas it would be far more likely to be beneficial for a species that is primarily carnivorous... Even given that, I think the popcorn analogy fits pretty well also.
Aloha,
Rob
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