European cuttlefish: A potential species for aquaculture - what we know so far
Cuttlefish are especially popular in Far-East Asian and Mediterranean markets, making them ideal candidates for aquacultural production from a market perspective. The viability of cephalopods in aquaculture has long been of interest.
This is largely due to a global decline in finfish stocks over the last century, which has subsequently led to an eight-fold increase in cephalopod catches over the same period. An ever-growing demand from major fish consuming countries for greater diversity in edible fish species further emphasises cephalopods potential in filling a niche in the seafood market.
Non-edible by-products of the cuttlefish can be used as fish meal, bait or even in the pharmacological industry. Excreted nitrogenous compounds can be utilised in integrated aquaculture systems to promote algal and bivalve production, showing their sustainable and additional economic potential.
Cuttlefish are also valuable model species in scientific research. Their complex nervous system and advanced sensory organs have been studied in the fields of physiology, neuroscience, immunology and molecular biology.
Natural habitat & biology
In the wild, the European cuttlefish is a demersal species found in the shallow, temperate waters of the Eastern Atlantic from the North and Baltic seas to warmer waters such as those of the Mediterranean and South Africa. Seasonal migration (predominantly vertical) occurs across its geographical range which often coincides with various stages of the life cycle, including mating and spawning.
Both mating and spawning typically occur between March and July, triggered by water temperatures of 13-15°C. Males carry up to 1400 spermatophores while females can lay between 150 and 4000 eggs, depending on their size. Eggs are laid in clusters and are attached to floating debris and seaweed in the water column. They have an incubation period of between 30 and 90 days, depending on water temperature.
Cuttlefish are visual predators, feeding on small molluscs, crustaceans and young demersal fishes. If food becomes scarce, they will often resort to cannibalism as a survival strategy. Juveniles may consume as much as 30 percent of their body weight daily that in turn leads to high growth rates. Growth rate also depends on water temperature, and average weights of adults in temperate regions can reach four kilograms and lengths (measured as mantle length) of up to 45cm. Subtropical populations tend to achieve smaller sizes, e.g. ~2 kg and ~30 cm.
The viability of farming cuttlefish
Recently, studies have shown that it is possible to rear cuttlefish in medium-scale extensive aquaculture settings in Europe. However, commercial farming of cephalopods has yet to be achieved at scale due to bottlenecks limiting their upscaling from laboratory to commercial production. The following factors are key to their successful culture:
• Behaviour (such as - stocking density, sex ratios).
• Growth and feeding rates (nutritional requirements).
• Environmental parameters (including temperature, salinity and light intensity).
The culturing of cuttlefish is of interest due to their high growthrates and the potential to rapidly-produce juveniles in a relatively short period of ~40-60 days. Juveniles are highly sought after in many countries, particularly in Portugal where they are considered a delicacy.
A drawback is that conventional aquaculture systems are not designed to facilitate cuttlefish production. Like most aquaculture species, cuttlefish can be housed in open, semi-open or closed seawater systems, and they require tanks with large bottom areas to accommodate their benthic behaviour.
Unlike shoaling fish such as sea bream and salmon, cuttlefish require varying stocking densities at different life stages. Hatchlings require stocking densities of 500 individuals per m2 and tanks with a minimum bottom area of 0.06 m2. Stocking densities for juvenile to adult life stages can range from 20-400 individuals per m2, with average tank bottom areas of one metre depending on the seawater system used.
For the reproductive life stage, cuttlefish are reared in tanks up to 9000L, with stocking densities of four cuttlefish per m2 and a sex ratio of two females to one male to avoid territorial conflicts and aggressive behaviour.
Other external factors including temperature, salinity, oxygen concentration, and water quality can also influence growth and reproduction. Mimicking wild-like conditions in the laboratory and, ultimately, on an industrial level has proven difficult to date but is attainable.
Nutrition, the key to successfully farming cuttlefish
Nutrition is one of the main bottlenecks to scaling up cephalopod aquaculture. This is because crucial research on nutritional requirements (including protein, lipid, and energy) in cuttlefish is lacking. Finding the correct balance of these requirements is key for commercial production.
Cuttlefish are protein-rich, with body compositions ranging from 75-80 percent protein on a dry weight basis. Thus, they require diets containing high levels of protein and amino acids to sustain growth and fulfil their energy demands.
Previous studies have stated that the particular metabolism of cephalopods must be considered when creating compound diets, ensuring optimal productivity and somatic growth in juveniles and reproduction in adults at later stages. Protein synthesis and retention are efficient in cephalopods, while protein degradation rates are often low. This allows some species to invest as much as 92 percent of their synthesised proteins into somatic growth.
Characterisation of the amino acid profile in the cuttlefish is important to understand the nutritional value of their diets and the additional roles of amino acids aside from metabolism. For example, certain free amino acids such as taurine, play important roles in their osmoregulation and the early developmental stages.
More research is required to understand the importance of other dietary macronutrients such as lipids and carbohydrates, as well as micronutrients such as vitamins and trace minerals. Recent research has led to the discovery that lipids and fatty acids are essential in the form of polar lipids (obtained from low lipid-containing prey such as crustaceans) for the production and maintenance of the nervous system in the planktonic life stage.
Little research has been carried out on the role of carbohydrates in the European cuttlefish's metabolism, however, it is understood that they may only play a minor role in egg composition and metabolic function of the animal.
Producing artificial compound feeds for cephalopods has had varying results to date. As previously stated, cuttlefish are visual predators and trials using feed pellets instead of live prey have often led to lower growth rates, cannibalism and aggression in the culture setting. An artificial diet that is palatable, visually enticing and meets the optimal nutritional requirements of the European cuttlefish has yet to be designed but could prove revolutionary in the upscaling of cuttlefish production.
So far, cuttlefish have been successfully cultured by feeding a diet of live and frozen mysid grass shrimp from hatchling to reproductive stages. These studies have shown potential increases in somatic growth as well as individual and overall fertility when fed frozen grass shrimp. This may be a result of the lower energy expenditure needed when feeding.
The use of live feeds such as shrimp is not without its issues, most notably the fact that the availability, maintenance, and storage of live feed candidates expend as much as 50 percent of the total labour required for cuttlefish aquaculture, indicating that live feed diets are not yet economically viable when considering commercial cuttlefish aquaculture.
More research is needed in the areas of cuttlefish physiology, metabolism, and raw materials to develop diets that are inexpensive, easily storable, and meet nutritional requirements for commercial production.
An ideal candidate for aquacultural production
The European cuttlefish has the potential to fill the market niche for an alternative marine protein source. Its short lifecycle makes it an ideal candidate for aquacultural production. While steady progress has been made, it is evident that the information available is still not sufficient to support the commercial farming of this species.
Nutrition continues to be the predominant bottleneck affecting its upscaling, largely due to its fundamental role in cuttlefish metabolism and growth and its linkages with secondary bottlenecks such asoptimal environmental perameters and behavioural tendencies.
Holistically approaching these limiting factors, with a focus on nutrition will be key to ensuring the viability of commercial cephalopod aquaculture in the future.
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