Fish farms

Seaweed are naturally eaten by most fish. Can be used in fish feeding as a major feed ingredient, inclusion being in the range of 10 to 100% or as a supplementary ingredient at inclusion level below 10%. Seaweed can be offered fresh or dried and ground as seaweed meal. Main us is as fishmeal replacer in most cases, and earlier studies have shown that diets containing 10-20% seaweed meal (and thus about 3-5% protein of the control diet) resulted in fish performance similar to fishmeal based control diet. At higher seaweed inclusion, the diet provides no sufficient protein to the fish and thus results in lower fish performance

In the commercial fish farming, wet feed usually consists of meat waste and fish waste mixed with dry additives containing extra nutrients, all formed together in a doughy mass. When thrown into the fish ponds or cages it must hold together and not disintegrate or dissolve in the water. A binder is needed, sometimes a technical grade of alginate is used. It has also been used to bind formulated feeds for shrimp and abalone. However, cheaper still is the use of finely ground seaweed meal made from brown seaweeds; the alginate in the seaweed acts as the binder. The binder may be a significant proportion of the price of the feed so seaweed meal is a much better choice. However, since the trend is to move to dry feed rather than wet, this market is not expected to expand. 

Fish, like any other organism, have specific requirements for its environment. In a culture setting, the optimal environmental conditions should be achieved in order to realise fast growth and a profitable production. Seaweed or ingredients made of seaweed may be of prime interest for use in fish feed formulations. Various seaweed ingredients can be used as additive to feed: Different seaweed species contain a variety of polysaccharides that may contribute to fish health.

Seaweeds are regarded as an important nutritional source in fish feed because of its content of proteins, lipids, vitamins and minerals. Even though total lipid content is generally low, seaweeds are still a good source of health promoting PUFA's compared with other foods derived from plant and animal sources (Rajapakse and Kim, 2011).

Their potential use as substitutes of protein and other ingredients such as alginates, pigments, fatty acids or potential as feeding stimulants could be applied to marine animal production by aquaculture, especially fish and molluscs. The advantages of incorporating seaweeds are not limited to an increase in growth rate but can in some cases include an improvement of protein assimilation. Davies et al. (1997)

In addition to growth is health and quality of the produce, Seaweed is and can be used to structure the fish feed mix, alginates are sometimes used as binders in fish feeds to influence faeces consistency. From a societal point of view and to assure sustainable growth of fish culture in general, minimisation of the use of raw materials originating from fish is necessary. Growth performance of fish fed with diets containing new feed materials should be at least comparable to growth when fed with commercial pellets that contain high levels of fish meal and oil.

Algae have the ability to clean waste water stream from fish farms and are already in use, added to the feed mix again. Macro Algae or seaweed do show an enhanced growth when growing in the waste water area of fish farms. Seaweeds are, like shellfish, extractive species which remove inorganic nutrients from the water column. At first cultivation was on ropes in ditches containing fish pond effluents, but by 1967 it was moved into the fish ponds themselves. This had the twofold benefit of the seaweed using the fish waste material as fertilizer and the fish eating the epiphytes, such as Enteromorpha species, that would otherwise become serious pests for the seaweeds. Control with tilapia (Oreochromis mossambicus) and milkfish (Chanos chanos) was satisfactory as long as the fish were removed before they started to eat the Gracilaria; larger fish were periodically removed and replaced by small fish.

This concept of poly-culture, or integrated aquaculture to use the more recent terminology, has since been utilized in many situations where the effluent from the aquaculture of one species, potentially threatening environmental damage, can be utilized by another species to its advantage, with a reduction in pollution.

Within an IMTA context these species can be applied to remove e.g. ammonia excreted by the finfish component. Research indicates that positive effects of cage aquaculture on seaweed production seem to be site and situation dependent. Suspended cultures of Gracilaria chilensis close to salmon cages reached a production of 800 g m-2 month-1 which was twice as high as at control (non-farm) sites. On the other hand, Halling et al. (2005) could not detect a fertilising effect of fish farm effluents on G. chilensis in open sea experiments close to salmon cages. Ulva sp. grown close to fish cages in the Mediterranean showed above background level growth when cultured within 150 meter of fish cages. This concurred with higher levels of N and P in the Ulva sp. found in species grown close to the cages (Dalsgaard and Krause-Jensen, 2006).

It is difficult to find specific information regarding fish feed mix used for the different species and conditions. Just include a few published report which got some attention recently.

The effects on growth, feed efficiency and carcass composition of rainbow trout (Oncorhynchus mykiss) of adding Porphyra dioica seaweed to the diet at levels of 5, 10 or 15% were studied by Soler-Vila et al. (2009). The control diet was a commercial trout diet without seaweed meal (diets where isonitrogenous and isolipidic). Results of this study suggested an effective inclusion up to 10% P. dioca in the diet without negatively influencing growth performance.

Wassef et al. (2005) studied the effect of adding 5, 10 or 15% of Pterocladia capillacea or Ulva lactuca as feed additives for gilthead bream (Sparus aurata) diet. The control diet contained only fish meal as protein source. Best growth performance, feed utilisation, nutrient retention and survival were achieved when the diets contained 10% P. capillacea or 5% Ulva lactuca. Interestingly, this study also showed that fish fed with a diet containing 10% Ulva lactuca had a greatly improved stress response when challenged by 5 minute air exposure when compared with the control diet to which no seaweed meal was added. These results suggest that in fish, stress response and probably disease resistance as well may also be improved with the inclusion of seaweeds in the diet.

Use of Porphyra purpurea meal for juvenile thick-lipped grey mullet (Chelon labrosus).Three isonitrogenous and isocaloric diets (control diet without seaweed Growth performance, survival and nutrient retention of red sea bream (Pagrus major), were improved when introducing 5% Porphyra spheroplasts by replacing 3% fishmeal and 2% starch in a formulated diet, where fishmeal was still the main protein source. Two diets with 4.5 and 9.0% protein of the control meal replaced by seaweed meal)were tested. Specific growth rate (SGR, expressed as % of total body weight) of the control diet was 2.99% while SGR values for the 4.5 and 9% seaweed inclusion diets were 2.65 and 2.47%,respectively. The authors mentioned that despite the absence of higher growth rates in diets with seaweeds, weight gain was still satisfactory. This because growth rates achieved in this study were in accordance and even exceeded values reported by others in literature (Papaparaskeva-Papoutsoglou and Alexis,1986; Kandasami et al., 1987; Yoshimatsu et al., 1992).

Moreover, seaweed inclusion levels in this study were very high with 16.5 and 33%, respectively. Therefore, the authors concluded that, even though the macro algae P. purpurea is of lower nutritional value than conventional ingredients in semi-purified diets for thick- lipped mullets, the (partial) substitution of fish meal by seaweed proved to be cost effective.

The advantages of incorporating seaweeds are not limited to an increase in growth rate but can in some cases include an improvement of protein assimilation. In the case of improved fish feed structuring a reduction in loss/waste.

From a societal point of view and to assure sustainable growth of fish culture in general, minimisation of the use of raw materials originating from fish is necessary.



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