The quest for sustainable and cost-effective fish feed ingredients is a continuous journey in aquaculture research.
As the industry strives for more environmentally friendly practices and reduced operational costs, scientists are looking beyond conventional feed sources. This search is leading to some surprising discoveries, from common pond pests like snails to innovative uses for macroalgal co-products and the vast potential of microalgae.
The goal is clear: develop alternative diets that support healthy fish, ease the financial burden on farmers, and contribute to a more sustainable future for global fisheries.
Another way of looking at pests
The solution may just be hiding in plain sight. The abundance of snails, Pirenella supracretacea, growing in the earthen ponds is always a cause of concern. One day, Edgar Somblingo, officer-in-charge at the Southeast Asian Fisheries Development Center-Aquaculture Department (SEAFDEC-AQD) at the Dumangas Brackishwater Station, started seeing it in a different light.
What he, like the rest, had considered as pest before, he now saw as a candidate feed ingredient in the cultured snubnose pompano (Trachinotus blochii) diet. It is a known fact that the fish eat mollusks in the wild.
Snubnose pompano is a high-value species and may be described as a “most edible fish” because of its size, taste, and texture profile. Historically, it thrived only in the high-salinity environment of marine waters. Now it can be raised in brackish waters as well.
Rearing and growout protocols are in place, making it relatively easy to raise. Fingerling supply is improving. Among the suppliers is the SEAFDEC-AQD’s hatchery seedstock division, which sells the species as newly-hatched larvae and fry.
What is there not to like? Farmers in the Philippines say that feed expenses could be slashed.
Currently, cultured pompano is fed with 100 percent commercial diets, which can represent 50 per cent of the operation costs.
Somblingo is leading research that studies the feasibility of the snail as a “cost-efficient alternative diet” in pompano.
In the experiment, one group is given only commercial feed, and the other a commercial diet supplemented with snails. The conclusion has yet to be released.
Should the commercial feed-snail combo diet be effective, it would provide a two-pronged advantage.
“If proven to be successful, fish farmers will be greatly benefitted. First, it could cut down the cost of pompano feeding, making the fish affordable for everyone. Next, pompano may be a biological control agent for the snail population – reducing the need for chemical inputs, such as molluscicides, in pond culture operations,” SEAFDEC-AQD said in a press statement.
SEAFDEC-AQD researchers have developed a keen eye for identifying abundant and readily available alternative feeds. In 2023, for instance, its team of experts released a study on inclusion of polychaete mud worms (Marphysa iloiloensis) in the Indian white shrimp (Penaus indicus) diet. It was established that with feeding even once a week, the diet can improve fish reproductive performance and offspring quality in the hatchery.
Macroalgal co-product
A study conducted in the U.S. showed the efficiency of a macroalgal co-product in juvenile trout diet. It showed that this can replace 100 percent fish meal (FM), with performance indicators comparable to diet with 100 per cent FM.
This feed formulation had similar final weight, weight gain, feed conversion ratio, protein efficiency ratio, feed intake, and specific growth rate to those using zero per cent, 33 per cent, and 66 per cent replacement of FM.
“This study clearly shows that the high (100N) inclusion of microalgae co-product in rainbow trout diets is comparable to FM-based diet, with no significant differences in growth metrics, fatty acid composition, and lower economic conversion ratio,” wrote authors Pallab K. Sarker, et al. in “Towards sustainable aquafeeds: microalgal (Nannochloropsis sp. QH25) co-product biomass can fully replace fishmeal in the feeds for rainbow trout (Oncorhynchus mykiss),” published in Foods journal.
The results indicate that the microalgal co-product “may be a practical approach to fully replace FM in rainbow trout feed.”
Nannochloropsis sp. QH25 co-product is a leftover after oil extraction for nutraceuticals.
In terms of dollar-per-kilogram of trout production, the conversion ratio is almost identical in fish fed with the reference of 100 per cent FM and fish fed 100 percent with microalgal co-product feed at $0.88 and $0.86, respectively. This result was traced to “slightly higher feed conversion ratio (FCR) in the microalgal co-product feed compared to the reference feed.”
The current scale and technologies available largely contribute to the price of Nannochloropsis sp. “It is predicted that with the emergence of large-scale facilities, the cost of microalgal biomass and feed will decrease, making it more competitive,” the study said.
Microalgae cultivation pathways
Microalgae has been identified as “a transformative alternative” fish feed. These have high-quality proteins containing all essential amino acids.
The trait is complemented by fast growth rates and being able to thrive in extreme environments. Water requirements, for example, can even be saline or wastewater. Under optimal conditions, biomass can grow by 100 percent within a few hours. It also has an active role in carbon capture.
As a food source, microalgae is not limited to animal feed but may be used for human food as well. It plays a role in the UN Sustainable Development Goals (SDG) for zero-hunger. It features prominently as well in about 50 per cent of the SDG, including climate action, clean water and sanitation, and affordable and clean energy.
Production, however, is hampered by several factors.
In the review, “Advancements and challenges in microalgal protein production: A sustainable alternative to conventional protein sources,” authors Sameh S. Ali, et al. provided a comprehensive analysis of the latest advancements, challenges, and future perspectives in microalgal protein production.
Microalgae cultivation of four primary metabolic pathways was discussed, specifically phototrophic, heterotrophic, mixotrophic, and photoheterotrophic. Of the four, phototrophic cultivation is the most widely used. The main requirements explain this. Sunlight is the primary source of energy and CO2 is the carbon source.
“This approach is highly scalable and suitable for outdoor biomass production, making it a preferred choice for large-scale operations,” they recommended.
Its downsides stem from light limitations in dense cultures, contamination risks in open systems, and high evaporation rates in outdoor ponds.
“To address these limitations, innovations in photobioreactor design and light manipulation are being explored. Closed photobioreactors (PBRs) offer better control over growth conditions but are energy-intensive and costly to operate,” it was cited.
Just like phototrophic cultivation, the three other pathways have their respective pros and cons in terms of suitability for large-scale production.
Scalability and economic feasibility remain major challenges in microalgal protein production, said the authors.
They emphasized the need for cost-reduction strategies, genetic engineering for enhanced yields, and industrial-scale process optimization. “By integrating innovative extraction techniques with biorefinery models, microalgal proteins hold immense potential as a sustainable, high-quality protein source for food, feed, and nutraceutical applications.”
The review was published in BMC.
