Residue of microalgae derived biofuel could work as fishmeal alternative in aquafeed

[South Korea] The authors, writing in the August edition of Aquaculture Research, found significant weight gain and a high growth rate for abalone fed a dry Nannochloropsis oceanica (NO) biomass residue in combination withcasein.

“The essential amino acids, such as isoleucine, leucine, phenylalanine, threonine and valine tended to increase with dietary substitution of fishmeal with NO biomass residue in the experimental diets,” added the scientists, based at the Korea Maritime and Ocean University and two Korean fisheries research institutes.

However, another essential amino acid, arginine, tended to decrease when the diet of the abalone was supplemented with the microalgae in question, they noted.

Hunt for protein alternatives

Since the mid-1990s, there have been many increasingly successful attempts to commercially farm abalone – edible sea snails.

The principal farming regions for the species are China, Taiwan, Japan, and Korea, but abalones are also farmed in Australia, Canada, Chile, France, Iceland, Ireland, Mexico, Namibia, New Zealand, South Africa, Thailand, and the US.

Abalones are known to be herbivorous and feed mostly on macroalgae. However, there is limited availability of the algae they typically consume, such as sea tangle Laminaria japonica and Undaria, during the winter season in Eastern Asia, said the authors.

Moreover, those algae species are somewhat deficient in protein content, so producers cultivating abalone are constantly on the lookout for other protein sources for their feed, added the scientists.

Casein is said to be effective in this regard but is reported to be too costly to be used in high quantities, while prices for fishmeal are sky-rocketing due to increasing global aquaculture expansion and high demand, said the team. Thus, there is huge interest within the aquaculture industry in novel protein inputs.

Microalgae residues from biofuel production

The potential use of microalgae biomass residue from biofuel extraction as an aquaculture or livestock feed ingredient is gaining traction, said the authors, as it contains a high level of protein. But, they note, that the availability of such an ingredient is, currently, limited.

Studies have shown, they said, that supplementation of 10% cyanobacteria, Arthrospira maxima and microalgae, Dunaliella salina, into commercial feed was effective in terms of improving the growth rate of greenlip abalone.

Other trials where abalone (H. midae) were fed a diet involving the replacement of 50% of fishmeal by either soy meal or Spirulina indicated the growth rate of the fish was comparable to abalone fed a fishmeal-basal diet, said the scientists.

So, on that basis, the Korean team looked at the effects of dietary substitution of fishmeal with the combined dry microalgae, Nannochloropsis oceanica (NO) biomass residue and casein on growth performance and carcass composition of juvenile abalone.

Study details

The authors said they randomly distributed 1,260 juvenile abalone into 18 litre plastic rectangular containers, and prepared five types of diets in triplicate. The control diet included 28% fishmeal and 13% soybean meal as the protein sources. The experimental diets, they said, involved the substitution of 25% (NO25), 50% (NO50), 75% (NO75) and 100% (NO100) fishmeal respectively with a combination of graded levels of dry NO biomass residue and casein.

A diet comprising salted sea tangle (ST), Laminaria japonica, was included in the study to compare the effect of the experimental diets on performance of abalone, said the researchers. The results They found that survival of abalone fed the experimental diets was higher than that of abalone fed the ST diet for 16 weeks.

Weight gain and specific growth rate (SGR) of abalone fed the NO100 diet were higher than those of abalone fed all other diets, said the team.

The researchers added that no significant difference in weight gain and SGR was observed between abalone fed the control and the NO25 diets. “The poorest weight gain and SGR were observed in abalone fed the ST diet,” they said.

Nannochloropsis concentrates

Meanwhile, Australian scientists, writing in the June 2014 edition of the journal Aquaculture reported that concentrates of the microalgae Nannochloropsis sp. and Dunaliella tertiolecta have the potential to replace or supplement fresh cultures, long regarded as a bottleneck in the
aquaculture industry.

Based at the School of Marine and Tropical Biology at the James Cook University in Australia, they said those two microalgae species produced concentrates that lasted two months of storage without significant change in the fatty acid profile or protein content, thereby spanning the typical four to six week hatchery rearing cycle.

On the other hand, concentrates of Entomoneis punctulata and Melosira dubia did not have good shelf-life, indicating that they may not be suitable commercially.

Nannochloropsis sp. and D. tertiolecta, which are well-studied, with established growth and nutrient parameters, exhibited excellent fatty acid and protein retention and are thus good candidates for off-the-shelf products,” wrote the Australian team.

Significant costs

Heather Welladsen, Megan Kent, Arnold Mangott, and Yan Li explained that there is a rising demand for microalgae from the booming aquaculture sector, but live microalgae is a bottleneck for the industry because of the cost and sensitivity of the cultures.

“Mass culture of microalgae for rearing larval and juvenile aquaculture species can represent 30- 40% of the hatchery operating costs, whilst culture crashes at critical points in hatchery runs can be devastating for production,” they said.

While dried or concentrated microalgae have been extensively studied as alternatives to fresh microalgal cultures, their wider acceptance has been limited, they added.

There are some notable exceptions, such as the North American Pacific oyster industry, which uses Skeletonema costatum and Thalassiosira pseudonana concentrates.

“Algal concentrates have good potential as supplements or replacements of fresh cultures […] and demand for a cost effective ‘off the shelf’ alternative to fresh cultures is driving research in this direction.”

Source: Aquaculture Research
DOI: DOI: 10.1111/are.12562
Title: Effects of dietary substitution of fishmeal with the combined dry microalgae, Nannochloropsis oceanica (NO) biomass residue and casein on growth and body composition of juvenile abalone (Haliotis discus)

Authors: Myung, S. H., Jung, W.-G., Kim, H. S., Kim, Y. E., Cho, S. H., Jwa, M. S., Kim, P. Y., Kim,
M. K., Park, M.-W. and Kim, B.-H.


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