Dr Thierry Chopin Putting seaweeds in your feed formulations
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Four studies dealt with grey mullets. Growth parameters were either not negatively affected or improved at substitution rates of 9-18 percent (with Ulva sp., Palmaria palmata). Three studies involved Atlantic salmon: substitution rates up to 15 percent (with P. palmata) showed no negative effects on growth parameters, lipid oxidation or eating quality (texture, colour and flavour). Substitution rates as low as five percent had a positive effect on body lipid content. One study on Atlantic cod showed no negative effects on growth parameters or survival at a substitution rate up to 30 percent (with Porphyra sp.). One study on meagre found a five percent substitution rate (with Gracilaria sp., Alaria sp.) not only did not negatively affect growth parameters, but it was advantageous for coping with biotic stressors and modulated metabolism. One study on yellow croaker showed that substitution rates up to 15 percent (with U. prolifera) did not negatively affect growth parameters or survival.
Seaweed substitutions in freshwater fish formulations
ishmeal is a main component of the feed used in many types of aquaculture. It is in high demand and can represent a major cost of an aquaculture operation. Moreover, there are some controversies about the efficiency and the environmental impacts of using smaller fish to feed larger fish. Consequently, substitution of fishmeal by other protein sources has been investigated in recent years, mostly considering land-plant proteins. As not many studies have considered using seaweeds as protein sources, we undertook a literature review and found 107 papers, in which a portion of the feed was replaced with seaweeds: 61 involved the culture of fish (40 of marine fish and 21 of freshwater fish), 24 the culture of crustaceans (shrimp, prawn, lobster), 11 the culture of mollusks (various species of abalone), 10 the culture of echinoderms (sea urchins) and one paper the culture of holothurians (sea cucumbers).
Seaweed substitutions in marine fish formulations
Twenty papers centered on various species of seabream (red, black, gilthead and silver). There were, generally, no negative effects on growth parameters such as growth rate, weight gain, feeding efficiency, or muscle protein at a substitution rate up to five percent seaweeds (Ulva pertusa, Ascophyllum nodosum), and in some cases at rates as high as 10-15 percent (U. pertusa, A. nodosum, wakame). In some studies, the growth parameters improved at a substitution rate as low as one percent (with Ulva extract). Other effects included improved lipid metabolism, increased red blood cell numbers, and increased disease resistance without impairing overall growth. Five papers focused on Asian and European seabass. For Asian seabass, growth parameters were not negatively affected at a substitution rate up to six percent (with Kappaphycus alvarezii), while European seabass tolerated substitution rates up to 10 percent (with U. rigida, Gracilaria cornea). One study showed a five percent substitution rate enhanced stress resistance in European seabass (with U. lactuca, Pterocladia capillacea). Five studies involved tropical fish (rabbitfish and white spotted snapper). They indicated that the substitution rates should be kept at 5-15 percent (with U. prolifera), as rates at 20 percent showed decreased body weight and specific growth rate (with G. lemaneiformis). A substitution rate as low as five percent increased antioxidant capacity in rabbitfish (with U. lactuca).
Nine papers focused on Nile tilapia. In most cases, substitution levels of 5-15 percent (with U. clathrata; U. intestinalis, Porphyra dioica) did not negatively affect, or improved, growth parameters including feed efficiency, nutrient utilisation, lipid levels, growth performance and body composition. In some cases, additional benefits, such as improvements of immune responses and a decrease in oxygen consumption, were noted (with U. rigida, Porphyra yezoensis). Levels of substitution above 20 percent (with Porphyra sp., G. vermiculophylla), generally, had negative effects on growth parameters. In the seven studies involving rainbow trout, the growth parameters mentioned above were not negatively affected at substitution rates of 5-6 percent (with G. pygmaea) and, in some cases, up to 10 percent (with G. vermiculophylla). In one study, the inclusion of Porphyra dioica at a level of 10 percent had no negative effects on growth and it enhanced the colour of the flesh at the end of the experiment. Other freshwater species, such as catfish and carp, tolerated 5-10 percent substitution rates (with G. arcuata) before negative growth effects were noted.
Seaweed substitutions in crustacean formulations
Inclusion of seaweeds (Ulva, Gracilaria, Porphyra, Saccharina) up to 20 percent substitution rate did not negatively affect the final product. In some cases, the inclusion of seaweeds (U. lactuca, G. vermiculophylla) increased growth, survival, immunity, feed conversion ratios, antioxidant activity and final weight. There were also examples of increased antioxidant levels, enhanced stress responses and improved enzyme activity (U. lactuca, G. vermiculophylla). Some visual differences were also noticed, such as a darker, more appealing, colour of the meat after cooking (with U. clathrata). However, inclusion of seaweeds (U. lactuca) at higher amounts (more than 50%) can negatively affect the final product in terms of decreases in survival, weight gain, growth and lipid levels. One exception was lobster, which tolerated inclusion at a rate of 50 percent (with Chondrus crispus, A. nodosum, kelp, and eelgrass) without a significant difference in growth.
Seaweed substitutions in mollusk formulations
The studies on mollusks focused on various abalone species, which rely mostly on diets of fresh seaweeds (Laminaria digitata, U. lactuca, P. palmata, Gracilaria sp.). In some cases, where the supply of fresh seaweeds is not reliable, this is supplemented or replaced with
20 | March 2019 - International Aquafeed