The Carry-Over of Fluoride from Krill Meal Pellets Into Rainbow Trout (Salmo Gairdneri)

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I~ternatlonal.Council for the C.M. 1981/ F:6 Exploratlon of the Sea Mariculture Committee

THE CARRY-OVER OF FLUORIDE FROM KRILL MEAL PELLETS INTO RAINBOW TROUT (SALMO GAIRDNERI)

by K. Tiews1). M. Manthey2) and H. KOOpsl)

1) Institut für Küsten- und Binnenfischerei der Bundesforschungsanstalt für Fischerei Palmaille 9. 2000 Hamburg 50 2) Institut für Biochemie und Technologie öer Bundesforschungsanstalt für Fischerei Palmaille 9. 2000 Hamburg 50 -.:I,', I ,

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ABSTR';cr

An experimental group of 70 9 rainbow trout fingerlings were fed krill meal pellets containing 2,500 mg/kg fluoride, and, a simila'r control group received the conunercial trout feed, "Trouvit", from 26 June to 17 October 1980. It was clearly shown that the fluoride content did not increase in the muscle tissue of the trout fed with krill meal pellets, but deposition of fluoride in the skeleton was considerable reaching concentrations as high as 3,100 mg/kg (wet weight). The regression of the increase withtime is linear. The fluoride content of the filets is similar to those of ~ filets from captured wild sea fish.

1. INTRODUCTION

As part of a research program carried out at the Institut für Küsten- und Binnenfischerei, Hamburg, to replace fish meal in pellet feeds for rainbow-trouts with other protein feed-stuffs, krill meal obtained during German Antarctic Expeditions was tested. Several 'experiments in 1976 and 1977 showed that it is an excellent replacement for fish meal in pellet feeds. The nutritional value of krill meal for the trout was found to be more or less equal to that of fish meal (Koops et al.,1979). In 1979, SCevik and Braekkan reported that they had found very high fluoride concentrations of up to 2.400 ng/kg fat free dry matter in Antarctic krill. The high fluoride content of krill was unknown at the'time of the feeding experiments. It was therefore essential to repeat the feeding experiments, in order to determine the amount of fluoride carry-over from pellet feeds containing krill meal to the rainbow trout. ~

2. MATERIAL AND METHODS

The experiments were carried out from June 26 to November 17, 1980 in conjunction with experiments on the protein-energy interrclation ships in rainbow trout feeds, described in full by Schwalb-Buhling

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Iab1e 1: Feed conversion rations for the perioö June 26 - October 17, 1980 (+) rations.used in protein-energy studies

Crude protein: ~ 45 40 35 30 Trouvit Krill 10 ·1.16+ 1.21+ 1.39+ 1.64+ 12.5 1.12+ 1.23+ 1.38+ 1.59+ - 1 ~.+ 15 1.16+ .,,~ 1.28+ 1.32+ 1.49 1.28

Ihe Trouvit ration had a fluoride content of 44 mg/kg. while 2.536 mg/kg was present in the krill meal ration. • The experiment clearly demonstrated the following (Iab1e 2): 1. There was practically no increase in the fluoride content of the skinless filets of rainbow trout fed the krill meal ration. Concentrations found were equal to those of rainbow trout fed the Trouvit ration. Ihey varied between 2 and 4.5 mg/kg (wet weight) • There was no increase with time. 2. There was only a relatively slight increase in the fluoride content of filets with skin of rainbow trouts fed the krill meal ration. Ihe fluoride content of the filets with skin was found to be roughly three to four times higher (4-16 mg/kg) than in the skinless filets. apparently because of storage of fluoride in the scales. 3. There was a very considerable amount of fluoride stored in the skeleton when rainbow trouts were fed the krill meal ration. Values up to ·3.143 Fe mg/kg were found (Iable 2). The regression of the concentration increase on time 1s linear. After 6 weeks on the krill meal diei. the fluoride content increased 6 fold. and after 11 weeks. 10 fold. After the krill diet was discontinued: the slight decrease in fluoride content which was o?served is not statistically significant. The increase of the fluoride content amounted to 190 mg/kg per week. corresponding to 30 ~g/kg per feeding day (6 feeding days per week). Table 2: Fluoride ~nt as F0 mg /kg (values refer to wet weight) ~two groups of trout. one fed ~rllJit pellets and the other. krill meal pellets #,« '~f t------"r------.-.--.--- '. f-.--.------tt------.------Trouvit Krill meal ...._... _- Sampling Total weight Fluoride content Total weight Fluoride content date or trout in g Filet Filet Skeleton or trout in g Filet Filet Skelt'l,'" with skin without skin with skin without skin

20.Vl.1980 65 1.6 2.9 207 68 1.9 2.7 263 , 71 2.4 2.2 312 11 2.9 2.7 233 ...... ~Z ~:~.•...•.. ~:~ •..•...•...~~~ ...... • l· 64.4 2.3 2.7 259 I s • 10.0 0.51 0.36 41 1------#------1I 13.VllI.80 95 4.3 228 109 8.8 4.0 1.31~ i i 118 2.7 192 134 7.3 2.5 1.145 I 11 3.2 272 98 9.4 3.0 1.739 I I 109 3.5 268 116 11.1 3.6 l,Z83 , ...... ~~ __ ._ _ ~:~ __ ~~Z . ···················································-1119 9.0 2.4 2 2!,2 ! x· ·95.4 3.5 237 115 9. 1 3. 1 1• 544 ; •• 18.8 0.60 33 13.2 1.36 0.69 449

17.X.1980 154 5.3 3.4 272 213 9.9 2.0 Z.721 231 2.6 1.6 182 195 4.4 2.9 2,144 227 3.1 1.3 195 212 13.5 2.2 Z,661 i 132 3.6 1.8 280 206 12.1 3.4 2,718 I ..... !Z~ ~:~ ~:~ ~2! ...... ~QZ ~:~ _ ~:Q ~.!~~ ! ll. 184.0 3.4 2.1 244 206.6 9.6 2.7 2,677 I •• 43.9 1.12 0.82 51 7.2 3.56 0.58 355 10. Xl.l980 278 3.5 2.6 251 193 10.1 4.5 2,454 201 3.3 2.3 369 228 10.3 2.4 :!,S74 257 3.5 3.3 208 240 14.6 3.3 2,655 156 4.5 2.8 288 192 16.3 4.1 I,R15 , .....!22 ~:~ ~:~ ...... •. !~~ ...... ~Z~ !~:Z_ ~:~ ~.Z~Z ' x. 218.2 3.5 2.7 256 225.0 13.2 3.4 2,~51 •• 49.0 0.71 0.38 79 33.7 2.82 0.94 372 I ,r ~'. /. >'"".., - 6 - Gravc (1981), who fed salmonids kept in net cages in Kiel Fjord for up to 3 years with frozen krill, also came to the conclusion that the fluoride content in the muscle tissue increased only slightly with time during the experiment. It never exceeded the concentration in several wild fish species from the North Sea. found by other authors. He also detected a considerable accumulation of fluoride in the skeletons of fish (up to 670 mg • kg-1 of dry matter). As the skeleton is not eaten. there seems to be no health risk for the consumer who eats rainbow trout raised on krill meal pellets according to our methods or fed deep-frozen krill' in the manner of Grave.

4. REFERENCES

Grave. H. Fluoride content of salmonids fed on Antarctic krill. 1981 Aquaculture, 24: 191-196. Koops. H.: Tiews. K.: Gropp. J. and Beck. H.: Krill in trout diets. 1979 In: Halver. J. and Tiews.K. (eds.): Finfish nutrition and fish feed techno1ogy. Vol. II. Schriften der Bundesforschungsanstalt für Fischerei 14/15: 281-292. Manthey. M.: Fluorid-Gehalte in antarktischen Fischen. 1980 Inf. Fischw. 27 (6): 261-262. Schwalb-Bühling. A.: Gropp. J.: Koops. H. and Tiews. K.: 1981 On the protein-energy interrelationship in rainbow' trout feeds. ICES. C.M. 1981. F:4 Soevik. T. and Braekkan. O.R.: Fluoride in Antarctic krill (Euphausia 1979, superba)and Atlantic'krill (Meganyctiphanes noryegica). Fish. Res. Bd. Canada. 36 (11): 1414-1416.