An international team of researchers in Brazil, Portugal and Spain examined the use of black soldier fly pre-pupae meal (HM) in the diets of European seabass, in place of fishmeal (FM). The group published its results in the journal of Aquaculture.
“This study aimed to evaluate the effect of dietary replacement of FM by HM on growth performance, plasma metabolic profile, feed utilization, apparent digestibility, and digestive enzyme activities of European seabass juveniles,” said the researchers.
The group found that levels of the pre-pupae meal could replace almost half of the fishmeal in the diet of juvenile seabass with few consequences to production, they said.
“This study indicates that up to 19.5% of black soldier fly (Hermetia illucens) pre-pupae meal (corresponding to 22.5% of dietary protein), may successfully replace 45% FM in diets for juveniles of European seabass, without any adverse effect on growth performance, feed utilization, apparent digestibility coefficients or digestive enzyme activity,” they said. “Further research testing higher dietary HM inclusion levels, as well as detailed economic analysis of its incorporation in the diets, are needed to better evaluate the potential of HM inclusion rates in commercial aquafeeds.”
Why fly pre-pupae meal?
Pressure to generate more food from aquatic sources, including aquaculture, has increased, said researchers.
Most farmed fish are raised on aquafeeds, and for carnivorous fish species, the diet often includes large levels of fishmeal and fish oil, they said. However, demand has increased the price of these feed ingredients.
Considerable efforts have been made to reduce the reliance on fishmeal and fish oil, they said. Interest has turned to sourcing sustainable supplies of animal and plant feedstuffs for aquafeed use.
“Attention has focused on the use of plant protein-rich feedstuffs in practical diets for carnivorous fish,” said the researchers. “However, plant feedstuffs have relatively low protein content, unbalanced essential amino acid profiles, low palatability, the presence of anti-nutrients, and competition with other food-feed industry sectors.”
This has encouraged work to improve the use of plant protein-based diets and for other alternative ingredients including animal feedstuffs and insect meals (IM), they said. “Compared to conventional animal protein, insects have several advantages, including being reared on discarded organic by-products with low water input, high feed conversion efficiency, emission of low levels of greenhouse gases and ammonia, few animal welfare issues, and low risk of transmitting zoonotic infections,” they added.
Insects offer a protein content of 60-80%; a well-balanced essential amino acid profile; and an alterable lipid and fatty acid profile, they said. The meal generated can be a good source of minerals including potassium, iron, calcium, magnesium and selenium.
Pre-pupae black soldier flies are of interest because there are already ways to mass-rear the insect for industrial production, the researchers said. They provide an average protein content of 55% dry matter and a balanced essential amino acid profile.
“Although HM is considered to have a nutritional value close to that of FM, replacement of FM by HM in aquafeeds has not yet been as successful as hoped,” the researchers said. “Maximum dietary FM replacement level has ranged from 6 to 25%, depending of the fish species, with highest levels being attained for rainbow trout, Oncorhynchus mykiss.”
In past experiments, the meal has reduced growth in channel catfish, rainbow trout and turbot when used at high levels, they said. “In salmon, Salmo salar, dietary supplementation with lysine and methionine allowed dietary HM level up to a maximum of 25%,” they added.
But little work has been doing exploring the use of insect meals on marine fish, they said. And those efforts have not included juvenile seabass.
Methods and materials
In the feeding trial, juvenile seabass were given one of four diets for 62 days, said the researchers. These included a control diet with fishmeal and diets with 6.5%, 13% and 19.5% of the pre-pupae meal replacing 15%, 30% and 45% of FM.
Fish were acclimatized to the trial conditions for 15 days, then 12 groups of 10 fish were established, they said. Fecal matter was collected during the trial and fish were weighed at the end of the feeding trial.
The apparent digestibility coefficients (ADC) of the diets were calculated for dry and organic matter, protein, amino acids, lipids and energy, they said.
Blood and intestinal samples were collected at the end of the trial, the researchers said. These were checked for enzymatic activity and plasma metabolites.
At the end of the feeding period, no differences were found among fish receiving the different diets in terms of growth performance or feed use, said the researchers. The insect meal was capable of replacing up to 45% of fishmeal without negatively altering growth performance.
“The fish promptly consumed all diets and no differences on voluntary feed intake were observed, indicating that HM was palatable for seabass,” they said. “Feed efficiency was also unaffected by dietary composition.”
Plasma metabolic profiles remained similar, but plasma cholesterol was lower when HM was added to the fish diets, they said. The ADC were high for protein, lipids, dry matter, organic matter and energy and were not altered by the trial diets.
The ADC of arginine, histidine and valine were raised in HM diets compared to the fishmeal only diet, said the researchers. But, lipase activity was reduced in HM 6.5 diet when compared to both the control and HM 19.5 diet.
Title: Black soldier fly (Hermetia illucens) pre-pupae meal as a fishmeal replacement in diets for European seabass (Dicentrarchus labrax)
Authors: Rui Magalhães, Antonio Sánchez-López, Renato Leal, Silvia Martínez-Llorens, Aires Oliva-Teles, Helena Peres