Amaranth leaf offers potential protein for fishmeal replacement

Tilapia growth and production supported on a 80% fishmeal replacement diet, say researchers.

An international research team involving scientists based in universities in the US and Kenya examined the use of vegetable-based proteins as fishmeal (FM) replacement in Nile tilapia diets.

The group published their work in the journal ofAquaculture Reports​.​​

“The objective of this study was to investigate the nutritional quality of [amaranth leaf protein concentrates] ALPC and the effects of replacing FM with ALPC in a formulated feed on the growth performance, nutrient utilization, carcass proximate composition and digestibility of Nile tilapia (Oreochromis niloticus),” ​they said.

In the trials, researchers found that production was sustained with fishmeal replacement levels reaching 80%, but that all fishmeal could not be replaced, they said. However, more work may be needed to improve processing of the plant for feed use.

“It may be concluded that ALPC can replace up to 80% FM in the diet of O. niloticus without compromising growth, nutrient utilization, whole body composition and nutrient digestibility,”​ said the researchers. “The reduced growth performance of fish fed diets with up to 0% FM may be related to the limiting level of methionine and leucine, high anti-nutritional factors which depressed the feed intake and growth in fish at high levels of plant protein.”​

Why amaranth leaf?

As farmed finfish production continues to expand, more high quality aqua feed is needed to sustain the industry, said the researchers. However, it also is putting increasing strain on limited amounts of fishmeal available.

Alternative protein ingredients are needed to support continued expansion of the aquaculture industry, they said. Several plants have been considered as partial or complete FM replacements because they offer a similar amount of protein and a good amino acid profile.

But when used as complete or partial replacements for fishmeal results have been variable, they said. “Therefore research into utilization of plant protein ingredients to replace FM will more likely continue,”​ they added.

Some plants in the genus amaranthus have been of interest because of the nutritional content, said the researchers. The plant also is quick growing and inexpensive to produce.

“Previous research has demonstrated that amaranth grain has hypocholesterolemic effects,”​ said the researchers. “For instance it was reported that diets containing 20% Amaranthus cruentus grains and 5% crude amaranth oil have a decreasing effect on total cholesterol and low- or very low density lipoprotein (LDL) in hamsters and hypercholesterolemic rabbits.”​

Bu, little work has been done evaluating the plant for use in aqua feeds, they said. 

Methods and material

In the study, Nile tilapia fingerlings were given diets with varying levels of fishmeal and an alternative protein generated from amaranth leaves, said the researchers. The feeding test ran for 160 days.

In the trial diets 100%, 75%, 50%, 40%, 20% or 0% of the fishmeal protein was replaced with the amaranth leaf protein concentrates (ALPC), they said. Diets were comprised of locally-sourced ingredients including wheat bran, brewery waste, perch oil, cassava and mineral and vitamin premix.

Ingredients, diets and fish were checked for moisture content, total ash, ether extract and crude fiber amounts, they said. Amino acid levels were also checked.

Fish were evaluated for performance, nutrient use, whole body composition, survival and for apparent nutrient digestibility, they said. The feed conversion ratio (FCR) and specific growth rate (SGR) also were calculated. 

Results​

“We demonstrate that it is possible to replace up to 80% of fish meal with ALPC without compromising the performance O. niloticus,”​ said the researchers. “These results demonstrate that although it is possible to replace [a] large part of fish meal with ALPC, it is not possible to eliminate it in Nile tilapia diet as alternative protein ingredient.”​

After 160 days, the research team found that fish getting diets that included more than 80% ALPC had reduced growth, nutrient utilization and a poorer FCR than those getting more diets with more fishmeal, they said.

“Treatments with 100% substitution levels of FM with ALPC resulted in lower final weight, weight gain and FCR,” ​they said. “Highest fish survival was observed in tanks with 100% FM, while diets where substitution of FM was done showed comparable survival (74–77%) regardless of the substitution levels of FM by ALPC.”​

Fish getting diets with lower amounts of fish meal had higher daily feed intake, they said. Carcass moisture and protein were not altered by the different diets, but lipid content was slightly lowered with more ALPC in the diet and body ash was increased.

Apparent nutrient digestibility for protein was best for fish getting diets with 100% to 40% fishmeal, said the researchers. However, lipid digestibility was similar for fish on all diets save those getting no fishmeal and carbohydrate and dry matter digestibility was comparable for all diets.

There were some challenges to the use of ALPC in the diet as it had a “considerable presence” ​of anti-nutritional factor, they said. And, except for potassium, fishmeal had a higher amount of multiple essential amino acids.