By Sara Leigo*
The main reasons are often the rapid deterioration of water quality due to disintegration of micropellets, and high mortality rates as a result of malnutrition or difficult digestion of diet compounds of feed. Therefore, larval stages of many marine species are still highly dependent on live food: phytoplankton and zooplankton.
Phytoplankton or microalgae are the basis of most marine food chains. Consequently, microalgae play a crucial nutritional role as a food source and as a feed additive for marine animals. Microalgae are used in aquaculture hatcheries for fish, shrimp, and shellfish larviculture, especially to feed live-prey such as rotifers which, in turn, are used to rear the larvae of marine finfish.
However, few microalgae species are suitable to use in aquaculture since microalgae must possess a number of key attributes to be useful for marine species rearing. They must have an appropriate size, an adequate biochemical profile and complete absence of toxins that may be transferred up the food chain.
Seabass, seabream, turbot and more recently red porgy and yellowtail are the most important species cultured in the Mediterranean Sea. The successful development of commercial farms in the Mediterranean basin has been made possible by several improvements, especially in zootechnical progress in live-prey production.
Nannochloropsis sp., Tetraselmis sp. and Isochrysis sp. are the most common microalgae species used in Mediterranean finfish hatcheries. These species present significant differences in size, shape and biochemical composition.
In the hatcheries, the microalgae cultivation is usually carried out in transparent polyethylene bags and fibreglass cylinders, prevalently under artificial light. Production costs of microalgae can represent a problem in any hatchery as it is expensive and often unreliable. Hatchery managers try to stem the rising costs of production and find other alternatives. Mediterranean hatcheries are managed relying on the following strategies: 1) purchasing microalgae from external suppliers or 2) technology improvements for in-house microalgae production.
Purchasing microalgae from external suppliers
Strategy 1 is evidenced by the increase on the commercialization of live concentrates, frozen pastes, freeze-dried and spray-dried microalgae which results in the minimization of microalgae production within the hatcheries.
Necton S.A. located at south of Portugal is an example of a company specialized in the cultivation and commercialization of microalgae for aquaculture. Victoria del Pino, Microalgae Business Manager, says that Necton S.A. launched its first microalgae concentrate for aquaculture in 2000, and since then they have developed a set of specialized microalgae concentrates which aim to solve hatcheries’ day-to-day problems.
del Pino explained the microalgae culture process carried out at Necton S.A. This begins with a high quality inocula in the laboratory under controlled conditions, to avoid contamination and optimise biochemical composition of the microalgae. After growing the inocula indoors, a culture scale-up takes place in PBRs (closed systems) placed outdoors. Biomass is harvested through a controlled centrifugation process. Water used in the process is treated with mechanical (ultra-filtration) and chemical procedures to avoid bacterial and protozoan growth. Microalgae cultures are controlled daily for nutrients, growth parameters, contaminants and biochemical quality.
According to Ms. del Pino, the concentrates are supplied as a liquid, as a frozen paste and as a powder, presenting the following features: high cell concentrations, suitable biochemical composition for several applications, long shelf-life, absence of preservatives and pathogens, and easy re-suspension in the water.
Necton´s products are being sought by two kinds of Customers, hatcheries that are totally dependent on external microalgae supply and hatcheries which are acquiring microalgae when internal production is not enough. Aquaculture business has been increasing and Necton will soon be operating an enlarged production facility which will quadruple its actual production and will allow the company to meet the increasing market demand.
Technology improvement for microalgae production
The second strategy mentioned above is being particularly observed in Turkey, which is one of the leading countries in the Mediterranean aquaculture sector. Hatcheries operate with intensive systems, which makes it impossible to have a continuous supply of algae. They are betting on technology to produce microalgae as they strive to become entirely independent from external sources, which is still a challenging goal.
Akva-Tek Hatchery Co., established in Izmir, is a successful example of this effort. Akva-Tek Hatchery produces 7 different species of sea fish (seabass, sea bream, meagre, dentex, common seabream, umbra and ocellaris clownfish). Its production capacity has reached more than 30 million fry per year. The hatchery has been using recirculating (RAS) technology since 2004 and continually conducting R&D studies in order to improve fry cultivation, including the live food production.
I had the opportunity to visit Akva-Tek and I was impressed when I visited the live food unit. This unit is dedicated to the production of microalgae, rotifers and Artemia nauplii in large quantities, to be used as live feed for fish larvae. RAS technology is being used in rotifer production.
Akva-Tek’s microalgae stock room has several microalgae species which are carefully maintained and are used to inoculate higher volumes.
They operate a sophisticated microalgae production system. Microalgae are grown in tubular photobioreactors, both outdoors and indoors. Dr. Yasar Durmaz, unit manager, explained that the weather in Turkey is very variable, being too hot during the summer season and too cold during winter. Having outdoor and indoor reactors ensures microalgae supply during the entire fish production season, as they allow better culture control -which is greatly affected by environmental conditions.
Though cultivating their own microalgae seems a reasonable option, I did not have access to CAPEX and OPEX costs of Akva-Tek facility. Several scientific papers reveal that 30 – 40 % of marine hatchery operating costs can be attributed to microalgae culture [Heasman, M. P., Sushames, T. M., Diemar, J. A., O’Connor, W. A., & Foulkes, L. A. (2001). Production of Micro-algal Concentrates for Aquaculture Part 2: Development and Evaluation of Harvesting, Preservation, Storage and Feeding Technology; among others].
Both strategies for securing microalgae supplies strongly rely on managerial decisions which are highly dependent on local economic factors such as labour costs, among others.
Procurement of good and reliable suppliers is also increasingly difficult. Victoria del Pino states that “A few years ago, Necton was one of the few players in the market. Prices were high as demand was higher than offer. Nowadays, more and more providers are entering the market resulting in a price decrease of 30%; therefore it is strongly advisable to check prices of microalgal biomass more often than was needed a few years ago. Purchasers of hatcheries now have a harder task, procure more suppliers and deeply check quality as new-comers can also offer low quality feed material”.
Sara Leigo has a degree in Marine Biology and Biotechnology and a Master in Aquaculture and Fisheries. She works at Necton, a Portuguese company specialised in the culture and commercialization of microalgae which is focused in several applications, mainly in specialty feeds for aquaculture (www.phytobloom.com). She has extensive experience in barramundi, Dover Sole and turbot production.