How Black Soldier Flies Used as Feed Impact Fish Microbiome

I have discussed in previous posts the importance of recognizing, "what you are is what you eat". I think most people recognize this statement for its value as related to another adage garbage in- garbage out. Basically, what you consume impacts your own health and nutrition. 

The same is also highly recognized for diet formulations for livestock, poultry, and aquaculture. Such information is critical for optimal production of a species in confined agricultural settings as well as the economics of the system.

With regards to BSF, we know what is fed to them as larvae impacts their own nutritional value in the end. For example, high carbohydrate diets (e.g., fruits) can result in increased fat content of the larvae. 

A study recently published by colleagues in the UK and Sweden in collaboration with Protix, Inc examined this from a slightly different perspective- specifically, the impact of the stage of the BSF (larva vs prepupa) as well as stage of processing (with or without fat) on the microbiome (the link is related to the microbiome of humans- but it gives a nice overview of the importance of such work) of fish being fed these materials.  Here is a link for a nice review article of microbiomes of marine fish.

The study in question is:

Huyben, D., A. Vidaković, S. W. Hallgren, and M. Langeland. 2018. High-throughput sequencing of gut microbiota in rainbow trout (Oncorhynchus mykiss) fed larval and pre-pupae stages of black soldier fly (Hermetia illucens). Aquaculture.

In the study, they used a control fishmeal diet and various combinations (ration of 70:30) of this diet with either BSF larvae; 1) control, 2) fishmeal with larvae, 3) fishmeal with defatted larvae, and 4) fishmeal with prepupae.

The major findings of the study were:
1- diet impact fish microbiome as it varied in fish across diets
2- data indicate using BSF could enhance some beneficial microbes to fish health

The data produced from this study are a great first step in understanding the trophic (layers) interactions between diet, consumer, and associated microbes. I think there is tremendous opportunity here to unite disciplines (as demonstrated by the diversity of authors on this paper) and figure out the appropriate feed formulations and benefits/restrictions of using such diets.

A couple of questions that come to mind from this study are:
1- What was the microbiome of the insects being used (did any of these microbes proliferate in the fish)?
2- What specifically were the insects fed when being produced for the study?
3-BSF produced by Protix were reared on a different diet than those produced by the researchers. Could this be a confounding factor impacting results (i.e., microbiome)?
4- How does shifting larval diet impact their microbiome and does this translate into impacts of the fish microbiome?
5- I recognize limitations of taxonomic resolution (i.e., clarity of identification and data interpretation), but are there microbes specific to fish that engage in gene transfer with microbes from the insects (i.e., do the microbes merge genetically)
6- Was there an assessment of antibiotic resistant genes in the insects before use and could this impact the fish microbiome?

These are questions resulting from reading the study which could be investigated in the future. I believe the authors laid a wonderful foundation on which to build additional research. 

Author

Jeffery K. Tomberlin, PhD, Excited about Microbes & BSF
Director, EVO Conversion Systems 
​Twitter: @FliesFacility