Chitinase activity and feeding insects

[Hendre]

Hey everyone. Since my bichir has been bullied away from food by a picky cichlid I have been mostly feeding her on the surface but the intake hasn't been enough so have started hand feeding with tongs, some fish pieces and also small Dubia cockroaches. We have many hundreds breeding at home, why not feed some to my fish.

People have warned about overfeeding insects due to a chitin buildup but through some reading have found something interesting; polypterus have Chitinase present in their stomachs, an enzyme that degrades chitin. Source here. Wild polypterus had insect matter in their stomachs between 20-30% of the time according to this study, which would make the presence of a chitin-degrading enzyme useful. Another study here shows an abundance of terrestrial insects such as termites and ants in Polypterus senegalus.



Knowing this it would probably be reasonable to mix a high volume of insects into the bichir diet without worry of stomach blockage. Alongside quality dry foods and frozen fish pieces. It would be handy in cases like mine where target feeding can improve food availability to polypterus in tanks where they are sometimes pushed from food. Thoughts?

 

[Hendre]

RD. Do you have any insights on Chitinase?

 

[Hendre]

Another thing to look at, Dubia roaches are only 3.5% chitin which is the lowest of these feeder insects. Given their gusto for gut loading it makes sense to use them as a feeder insect.

 

[Josh's Fish]

Hi Hendre, thanks for linking this to me, I'll share what we discussed on messenger.

Chitinase is a fantastic enzyme which helps to break the bonds of chitin. It allows Polypteriformes to include insects in their opportunist diet. This enzyme isn't a perfect solution though, these fish aren't predominantly insectivores, and also lack a gizzard which helps with this far better.

Like all localities of wildlife, they have worked into their own ecological niche. Populations with more avaliable insects will likely have more Chitinase enzymes to allow for more insects in their diet, whereas its mostly piscivorous counterpart in an adjacent river system would not be as efficient in digesting those insects.

A good example of this is just feeding more insects in aquaria. Things like mealworm chitin or cricket legs can still exit undigested. The concentration of this enzyme will not be universal across all Polypterus. The only Polypterus species I know to digest insects better than others are P. palmas and P. palmas "buettikoferi", and this may be because they're caught with clap nets in shallow and slow moving tributaries, where insects are plentiful.

Enzymes are costly to make, so if you do feed more insects, consider deshelling or feeding soft grubs. While feeding insects is not harmful, if you feed more insects at a rate faster than they can produce enzymes (which will differ with some species or individuals), much of those chitin bonds will not be broken and shells will still pass undigested.

Certainly don't stop feeding insects, but always check your Bichir's waste after feeding insects. If you see undigested chitin in it, you know you need to feed less of it for that individual!

Hope this helps!

 

[Hendre]

She has very quickly recognised tongs as food, roaches are a new favourite!