ECOLOGICAL FISH FEEDING STRATEGIES IN AQUACULTURE

Transcription

1 Analele Ştiinţifice ale Universităţii Al.I.Cuza Iaşi, s. Biologie animală, Tom L, 24 ECOLOGICAL FISH FEEDING STRATEGIES IN AQUACULTURE BY COSTICĂ MISĂILĂ 1 Keywords: aquaculture, fish feed management; trout and carp diets, water quality Starting from the existing literature data, and also backed up by the results of his own investigations, the author of the study synthesizes the relations established between the basic elements of the fish feeding management in aquaculture. The leading idea considered is that, with a view to contributing to the society s durable development, aquaculture should harmoniously combine the economic with the ecological concerns. Consequently, a performant feed management should maintain aquaculture as an efficient human activity, affecting in no way the ecological equilibria of the aquatic ecosystems. Besides evidencing the importance of precise knowledge on the ecosystem s natural food, the basic aspects contributing to a suitable selection of the additional feeds are analysed, together with the methods for their processing, storage and administration. The paper demonstrates, as based on original data, that in the case of both cyprinides and rainbow trout, the utilisation of qualitatively inadequate or of unsuitably processed feeds, alongwith the selection of unproper feeding methods or rations in exces reduce the fish production, cause a higher catabolite ratio and higher ratios of noningested food. At the same time, some concrete measures for the protection of the aquatic medium for aquaculture are put forward. Introduction Closing of the second Millenium finds out the worldwide aquaculture as a human activity in definite progress. Only over the period, the rhythm of aquaculture development all over the world was of about 11%. On the other hand, the total farmed fish production exceeded 3% of the global aquacultural biomass, (fig.1) and increased 3 times in this period, from 1.2 million tonnes, i.e. 11.4% of total fisheries landings in 1994, to 39.4 million tonnes, i.e. 31.1% in 1998 (MISRA et al., 23). Such a trend is based on the increased availability and large-scale utilization of aquaculture feeds, paralleled by improved methods of water quality management, disease control and general performant tehnologies in fish husbandry. Nowadays, most developing countries and many developed ones have extended the use of artificially compounded aquafeeds for farmed fishes and invertebrates. This is due to their extremely profitable character, for both breeding of less valuable from an economic viewpoint species, although largely utilized in the alimentation of poor countries 1 Al.I. Cuza University of Iaşi

2 Costică Misăilă people, facing the problem of insufficient food (carp, tilapia and catfish), and high valued species intended for luxury and rich markets from the developed countries (shrimp, salmon, trout, yellowtail, seabass, a.s.o.). Million tonnes Fig.1: World fish production between 1994 and 1998 (MISRA et al., 23) % % 1998 Fig.2: World aquafeeds production between 199 and 2 (CHAMBERLAIN, 1993) Million tonnes Fish feeding management in aquaculture The increased use of aquafeeds has stimulated the rapid development of the production sector, which became one of the fastest expanding agricultural industries in the world. Some statistical data evidence the increase of the world aquafeeds production (fig.2) in the decade, from 2.9 to 4.6 million tons, which means an average yearly growing ratio of up to 3% (CHAMBERLAIN, 1993; TACON, 1996). Such a tendency of modernizing fish feeding in aquaculture was manifested in Romania, as well, starting with 1989, both by the stimulation of performant feeds imports and by the realization of autochtonous receipts. 244

3 Ecological fish feeding strategies in aquaculture A suitable managemet of farmed fish feeding in aquaculture should be based on a holistic approaching of the phenomena, so that to reach optimum levels of efficiency and profitableness, without affecting, in any way the ecological balance within the ecosystem. In other words, the economic interests should harmoniously match the ecological one. That is why, the researchers concerns remain still focused on the preparation of diets that should fully meet the alimentary requirements of reared organisms, known as varying considerably from one species to another, or even within one and the same species, among individuals of different age or sex (for example, with the same food, common carp and eel females grow faster than male fish, unlike the channel catfish and tilapia, male fish, grow faster than female fish). According to the fish feeding habit (herbivorous, omnivorous or carnivorous), a certain assortment structure of the diets is selected. The selection criteria of the ingredients incorporated include both their chemical composition and cost, and equally their digestibility level, so that the ratio of catabolites released in the environment should be minimum. Also, the quality of the raw materials and finite products handling and storage, alongwith the feeding method employed and amount of daily ration represent significant elements, conditioning the extent of food acceptance and consumption, the quantity of noningested wastes included, and especially bioconversion efficiency. Consequently, by mens of food, one may control both the amount, quality and cost of the production obtained on one hand -, and the health condition of the captive fish stock, the quality of basins water (fig. 3), especially, on the other. 3. Selection of the adequate fish food type The most important element in fish feeding managemet is the selection of appropriate feeds, able to satisfy all nutritional requirements of farmed fishes. The three categories of feeds commonly used in aquaculture are: wet feeds with moisture contents of 5-7%, moist formulated feeds with moisture contents of 2-4% and dry pelleted feeds with moisture contents of less than 1%. Since problems are associated with the distribution, handling, utilization, storage and quality of wet feeds and moist feeds, more and more dry feeds are manufactured either by steam pelleting or by extrusion pelleting. The results of the nutrition investigations performed all over the world have been materialized in the existence of several fodder types, meeting the requirements of a large range of options, as to: diversification on species and age; control of floatability; particle stability in water; pigmentation degree; the protein/energy ratio; the content of drug substances; pollution prevention, a.s.o. 245

4 Costică Misăilă A proper selection of the adequate fodder assumes firstly knowledge of the six major classes of nutrients that assure the organism s energy and take part in tissues maintenance and growth: proteins, lipids, hydrocarbons, minerals, vitamins and water. The optimum physiological requirements for such nutrients differ considerably as a function of species, age and sex, and equally as a function of the available natural food. Thus, a diet containing 3-35% crude protein is vieved as optimum for carp rearing, while the optimum amount of protein for the rainbow trout lies between 38 and 5%, namely: 38-42% for the one year old rainbow trout; 4-45% for fry and fingerling 246

5 Ecological fish feeding strategies in aquaculture ones, and, respectively 45-5% for the sires (BATTES et al., 1975; MISAILA et al., 1976; WATANABE et al., 1987; MORALES et al., 1994). One should mention the fact that attainment of the percent level of raw protein in the diet is a necessary, yet not sufficient condition, once known that, simultaneously, at least two other legal requirements should be met, related on the side -, to the nature of the incorporated protein and on the other - to the protein/energy ratio in the diet. For example, in rainbow trout feeding, besides the large amount of raw protein required in the diet, it is necessary that at least 5% of this protein should be of animal origin, while in its turn - half of it should come from fish meal, an aspect much less restrictive in the case of common carp and other reared cyprinides. The strict observance of such requirements is sometimes neglected in practice, the economic losses recorded evidencing the necessity of a professional type of feeding management. Our data evidenced that the production losses caused by protein deficiency in the common carp diet amount to 28.4% (fig. 4), while the percent ratio decrease between the animal and the vegetal protein (AP:VP) in the rainbow trout diet (fig. 5), from 44: 56 to :1, caused a production loss of 51.7% (MISAILA et al., 199; 22). g/piece/162 days Fig.4: Common carp weight gain as a function of food protein level 633 1% % FCP = food crude proteins % 4% FCP 3% FCP 2% FCP 1 A B C Variants 247

6 Costică Misăilă Fig.5: Rainbow trout weight gain as a function of AP:VP food percent ratio g/piece/1 days AP = animal % animal proteins proteins 1% 53.9 VP = % vegetal proteins 9.7% % % AP:VP 44:56 AP:VP 2:8 AP;VP 6:94 :1 44:56 2:8 6:94 :1 A B C D Variants Nevertheless, the proteins from the recipe may be saved through their partial substitution with lipids or even carbohydrates, on condition of keeping an optimum protein:energy (P:E) ratio. For example, for the normal development of common carp juveniles (C 1+ ), the value of the P:E ratio is of 9-95 mg/kcal (MAGOUZ, 199) while, for the common carp fryies (C + ), the value recommended for this ratio is of 19 mg/kcal (MEDALE & GUILLAUME, 1999), worth mentioning being the fact that its possible diminution, up to 75 mg/kcal, might be obtained by substituing the protein with easilydigestible lipids, which does not affect fish growth. Increasing the lipid level in common carp food by addition of fish oil, as well of soya and sunflower oils - led to certain additional production growths, up to 6-7% (STEFFENS, 1977). In the case of the production carp (C 1+ ), fed with low protein level diets (27-33% crude protein), fodder s plastic performances were improved by the addition of sunflower oil. Therefore, the partial substitution of the protein with 5-1% lipids (fig. 6), resulting in decreasing of the P:E ratio from 11 to 73 mg/kcal led to the obtention of some supplementary weight gains of 12-26%. A possible explanation might be that the organism s energetic requirements are taken over by the lipids, wihe the proteins are more efficiently employed for plastic purposes. An important characteristics of the additional aquafeeds is the presence in their composition of some ingredients of fishing origin (such as fish oil, fish meal, crustacean byproduct meals, trash fish etc.). Such products represent between 5-7% by weight of compound aquafeeds for most farmed carnivorous finfish species, and between 25 and 5% by weight of the marine shrimp diets (MISRA et al., 23). 248

7 Ecological fish feeding strategies in aquaculture g/piece/64 days Fig.6: Common carp weight gain as a fonction of P:E food ratio 8 P:E = protein:energy proteins : energy (mg/kcal) % 126% 1% mg/kcal mg/kcal. A B C 73.7 mg/kcal. Variants mg/piece/6 days Fig.7: Rainbow trout fry weight gain fed with Spirulina biomass as partial (trial 1) and total (trial 2) substitute of fish meal % 97.5% % Trial 1 Trial 2 S = Spirulina S = Spirulina % Control Control S 1% 1% Control S 1% As the necessity of fish meal exceeds by far the predictable stocks, several alternative ingredients, that might support a durable development of aquaculture in the present millenium, have to be considered. Among such alternative ingredients of animal origin, mention should be make of: meat meal, blood meal, shell fish meal, flour obtained from poultry farming subproducts, etc. The list of substituents of vegetal origin is much more ample, including different types of biomass (of bacterian, algal and fungus type), as well as soya, sunflower or even cereal groats. Replacement of fish meal represents quite a laborious step as, besides its high protein (6-65%) and energy (2.72 kcal/kg) content, this fodder type is characterized by a total digestibility of the forage (TDF) of 7%, and a biological value of the proteins (BVP) characterized by a high content of essential aminoacids, especially methionine, cystine and lysine, 72% of these essential aminoacids occurring as balanced ratios. 249

8 Costică Misăilă Usually, a group of 2-3 ingredients is being formed (meat meal, soya groats, fodder yeast, wheat bran, dicalcic phosphate, fodder aminoacids, etc), in precisely calculated participation ratios, able of substituting a certain fish meal ratio. The unidirectional fish meal substitution, especially with vegetal non-balanced kinds, defficitary of essential aminoacids, causes significant retards as to fishes bodily weight (figs. 7 and 8) to which in the case of trout and of other carnivorous species certain perturbations of the alimentary behaviour should be added, such as exacerbation of cannibalism (MISAILA et. al 198; 1981a; 1981b). The advances recorded in the substitution of fish meal with alternative ingredients are related both to the development and utilization of modern techniques of aquafeeds processing and production, and to the elaboration of some new diets, extending the utilization of some specific additives, such as feeding stimulators, free aminoacids, fodder enzymes, probiotics, immunostimulators, etc. In this way, the ingredients digestibility and the biological value of the incorporated proteins are improved, while the ratio of catabolites released in the growing medium is reducing. For example, incorporation of natural zeolites from vulcanic tuffs in the concentrated food of farming animals has benefic effects on the general physiological condition, the growing increase included, as well (MUMPTON et al.,1977; TORII, 1978). The observation was made that enriching of the rainbow trout s food with 15% Mirsid tuff (MISAILA et al., 199) induces an additional weight gain of 14% (fig. 9). Fig.8: Weight gain in rainbow trout fingerling fed with Cladophora and Scenedesmus biomass as partial (5%) fish meal substitute g/piece/8 days % % % Control Cladophora Scenedesmus Variants 25

9 Ecological fish feeding strategies in aquaculture Weight gain (g/piece/77 days Fig.9: Weight gain in rainbow trout fingerling fed diet containing 15% natural zeolites from Mirsid volcanic tuffs % 114% 35 1% Control Tuff 15% Variants Such effects may be explained by the more efficient utilization of the nitrogen present in food (the protein retention increasing with 16%), as a result the additive s protective effect versus the toxic levels of the ammonium occurring in the digestive tract. 4. Selection of the aquafeeds processing, handling and administration methods A suitable and relatively uniform grinding of all ingredients from the diet contributes to the obtention of a homogeneous mixture, increases granule s stability in water and favourizes an uniform access and the hydrolyzing action of the digestive fluids. Even the raw materials with a superior chemical composition will give poor results if grossly ground. For example, only fine grinding of the soya groats, which represent 1/5 of the trout diet (fig. 1), leads to additional growth increases, up to 1%, comparatively with an identical composition diet, yet with grossly ground soya groats Besides the increase of the plastic performances of diets, a fine grinding of the compounding raw materials represents, too, a means of protecting water s quality, if considering that the more complete assimilation of the ingested food lowers the content of catabolites released in the environment. Feed pelleting for aquaculture represented an immense leap, regarding both fish balanced feeding with modern diets, including vitamino-mineral, biostimulating, drug, immunoprotecting microcomponents and reduction of the losses of noningested food, which increases nutrients input into the ecosystem. More than that, besides an easy handling and the advantages of storage and preservation they present, pelleted fooders permit a perfect sizing of alimentary particles to fishes dimension, favourizing the introduction of automated feeding in industrial-type farms. All such facilitaties brought about an unparalleled extension of granulated food application in aquaculture. Some researches (MISAILA et al., 1995) performed on the common carp evidenced that granulation increases fodder s price by 1-15%, however, the additional production thus obtained may exceed by 5% the one attained with an 251

10 Costică Misăilă identical composition, yet nongranulated diet (fig. 11). Finally, it is obvious that the fine ingredient grinding and a optimal finished feeds particle size, which affects the growth and feed conversion efficiency, represent equally important management elements, from both economic and ecological points of view. g/piece/77days Fig.1: Weight gain in rainbow trout fingerlings, as a function of grinding fineness of the soya groats from diets % 11.1% Control Fine groats Variants g/piece/145 days Fig.11: Weight gain in common carp, as a fonction of the type of supplementary food 165 1% 1% % 152.7% UNPELLETED PELLETED Variants Storage of dry, pelleted diets requires optimal levels of moisture and temperature. Under poor storage conditions, serious problems in feeds may arise from loss of vitamins, contamination with toxins, very dangerous for fishes, and from the effects of oil rancidity. The aquafeds preserved in deposits should be labelled in 252

11 Ecological fish feeding strategies in aquaculture accordance with national and international regulations in force, a strict inventory of the inputs and outputs being made. However, in some fish farms, the classical administration of unpelleted feeds, preceeded by their moistening, is still applied. Also, dry pellets are administered using the traditional hand feeding method, except of a few modern marine farms or some intensive or superintensive, freshwater stockfarms, in which automated feeding devices have been introduced. They may be operated by means of a programmed clock or through self-feeding of fishes which, on the basis of conditioned reflexes, provoke the release of some parts of their daily ration. In aquaculture, the daily food ration is calculated as a percent of total weigth of the fish population from an aquaculture pond. To this end, feed equations or feeding charts establishing the necessary percent as a function of fish size, water temperature and total biomass of the batch are applied (LEITRITZ, 1969; GUILLAUME et al., 1999). Besides feeding in restricted amounts (according to the ration), food administartion ad libitum (i.e., in excess) up to apparent satiation is practised, for catching the moment in which fishes start not eating, any more. The literature data recommends, with a certain reserve, of course, feeding ad libitum, as well as the utilization of feeding devices based on conditioned reflex, as a result of a higher food consumption - in spite of the fact that the increases recorded exceed the ones obtained by rationalized feeding. For example, in the case of the one year old rainbow trout, reared in cages and fed ad libitum (MISAILA et al., 1979), an additional production of 41%, has been obtained, comparatively with the rationalized feeding (fig.12), at an additional feed consumption of 35%. From an ecological viewpoint, of special interest are exclusively the feeding methods of limiting as much as possible the losses of non-ingested food. These leftovers become organic wastes which, together with the dead natural biomass and the excretory products (catabolites) released by the fish under culture, is associated with high BOD, the toxicity of NH 3, SH 2 and CH 4 contributing to the eutrophication and, further on, pollution of the ecosystem in which the aquaculture is practised. 5. Influence of aquaculture on water and sediment charging with nutrients Naturally, both water and the sediments of aquatic basins are exposed to an evolutive process of nutrient accumulation which, depending on the local hydrometeorological and biological conditions, may be slower or faster. Since the introduction of aquaculture activities, the eutrophising pressure upon the ecosystem has been considerably higher. Theoretically, any agglomeration of captive and artificially fed fishes induces a local organic water and sediments charging, which is proportional to the reared biomass. The main overflown nutritive elements are C, N and P, however, such elements produce unequal effects on the eutrophication processes. According to STUMM et al. (1971), the algal N requirement is more than 16 times higher than that of P, so that small P amounts may eutrophise to a considerable extent, which means that P may serve as a synthetic index of some water s organic charge. 253

12 Costică Misăilă A rainbow trout commercial diet, with 4% crude proteins, contains around 1.5% P (TACON et DA SILVA, 1983), which means that, with each tonne of pelleted food, 15 kg P are being introduced into the ecosystem. If the FCR value is 1, there follows that this amount of P is introduced into water for each tonne of produced trout. From this input, the amount of P fixed in the carcass (,48%) - i.e., 4.8 kgp/tonne of fish is subtracted, thus resulting a remanent charging of water and sediments of 1.2 kg P for each tonne of delivered trout. If diet s digestibility and the biological value of proteins are lower, the FCR value increases and, consequently, the amounts of remanent P also arise, reaching values of 32.7 kg/tonne of fish, if the value of food conversion is of 2.5 (fig. 13). Fig.12: Weight gain in the one-year-old rainbow trout as a function of feeding method g/piece/1 days % 141.9% RATIONALLY AD LIBITUM Variants Fig.13: Remanent phosphorus into water in rainbow trout fed with six diets containing 4% crude protein, but different FCR values kg P / tonne fish produced FCR values (kg ingested food / 1 kg weight gain ) Apart from their theoretical character, such calculations evidence the amplitude that the uncontrolled exploitation of the aquatic resource might reach, alongwith the 254

13 Ecological fish feeding strategies in aquaculture absolute necessity that the management of fish feeding, in aquaculture, should be viewed as a basic concept, substantiated on strategies of both economic and ecological nature. Conclusions 1. In order to preserve aquaculture s benefic character for mankind, this activity should efficiently produce useful biomass, in parallels with maintaining the quality of the aquatic environment. Such purpose requires, beyond any doubt, a professional type of fish feeding management, capable of obeying both economic and ecological criteria; 2. The literature data, our own results included, evidence that the utilization of qualitatively unsuitable or unproperly processed fodders, alongwith the application of inadequate foddering methods or excess rations reduce the production of both cyprinides and rainbow trout and increases the catabolite ratio and that of noningested food; 3. The measures taken for protecting the quality of the aquatic medium, already in force in some reputed in such problems countries, e.g., Demnark, Norway, France, etc., represent conditions for obtaining the notifications necessary in aquaculture farms operation referring mainly to: making the farmers conscious of the necessity of a suitable processing of the raw materials, as well as the utilization of granulated fodders, which assures the protection of water s quality; prohibition, by legal means, of unsuitably conditioned fodders, with ecologically unacceptable digestibility; permanent granting of a strictly specialized technical assistance, for the fish farms; adequate equipments of the nutrition laboratories, that would permit differentiation of the authentic fodders from the forged ones, containing substituients with unsuitable digestibility, as well as the possibility of an operative control of the catabolite ratio. References 1. Battes, K. W., Misaila, C., Artenie, Vl., Brevet RSR nr Chamberlain, G.W., World Aquaculture, 24 (1): Cutuhan M., Symp.on prod and use of fish meal, Bucureşti, C, 1-C Guillaume J., Kaushik S., Bergot P., Metailler R. (ed), Nutrition et alimentation des poissons et crustaces, INRA Editions, IFREMER 485 p. 5. Leitritz E., Die Praxis der Forellenzucht, Ed.P.Parey, Berlin, New York 6. Magouz F.I., Studies on optimal protein and energy supply for tilapia (O. niloticus), in intensive culture, Teza de doctorat, Univ. Gottingen- Germania 7. Medale Francoise, Guillaume J.,Nutrition energetique, in:guillaume J. et col. (ed.), Nutrit. et alimentation des poissons et crustaces, INRA Ed., IFREMER 485 p. 8. Misaila C., Battes K.W., Artenie Vl., Brevet RSR nr Misaila C., Misaila Elena. Rada, Tr. St. Stejarul, Limnol. 7,

14 Costică Misăilă 1. Misaila C.,Artenie Vl., Trav.Station Stejarul, Limnol. 8, Misaila C., Misaila Elena Rada, Caraus I., 1981a - Trav.Station Stejarul, Limnol. 9, Misaila C., Misaila El. Rada, Caraus I., 1981b - Trav.Stat. Stejarul, Limnol. 9, Misaila C., Misaila Elena Rada, Referat ştiinţific parţial, tema ICAS, 8., 46, D 14. Misaila C., Misaila Elena Rada, Marton Al., Bucur N., Lucr.S.C.P. Piscicolă Iaşi, 1, Misaila C., Misaila Elena Rada, Lucr.S.C.P. Piscicolă Iaşi, 1, Misaila C., Watson J., Misaila Elena Rada, Lucr. Simpoz. Internaţ. AQUAROM 95, Galaţi, Misaila C., Misaila Elena Rada, 22 Analele Şt. Ale Univ. Al.I.Cuza din Iaşi, vol. omagial, Misaila C.K., Das B.K., Mohanta K.N., 23 - Farmer International file, vol. 17, 1, şi vol.26, 2, Morales A.E., Cardenete G., Dela Higuera M.,, Sanza A., Aquaculture, 124, Mumpton Fr. A., Fishman P.H., J. of Animal Sci., vol.45 (9) 21. Steffens W., Fish Nutrit. and Feed Develop., Internat. Seminary, Hungary, Stum W., Leckie J.D., Adv. Water Pollut. Res., 5 (III-26): Tacon A. G. J., Da Silva S. S., Aquacultura, 31, Tacon A. G. J., Internat. Milling Directory, Uxbridge, Turrer-RAI, Torii K., Nat. Zeol. Occ. properties use, ed. Sand L.B., Mumpton Fr.A., Perg. Press, Oxford and N.Y.,