Fermented Organic Matter as Possible Food for Rearing Anguilla japonica Leptocephali

뱀장어(Anguilla japonica) 자어 먹이로 유기물 분해산물의 활용 가능성

Abstract

We prepared flocculated detritus-like organic marine snow originating from various organisms by fermentation using microorganisms; this fermented organic material was fed to the leptocephali of the eel (Anguilla japonica) to investigate whether or not such organic matter was an appropriate food source for the larvae. A strain was isolated from a biofloc technology system used to culture fish, and seven types of organic material from hen's egg, eel muscle, tuna muscle, lugworm, shrimp, manila clam, mussel, and sea squirt were fermented using isolated bacteria (Bacillus sp.). The fermented matter did not show any specific form and was larger than $10-20{\mu}m$ but no more than $100{\mu}m$ in size. Four diets (A-D) were prepared using the various fermented products, and the larvae were fed the prepared food from 20 days after hatching. The leptocephali fed the A, B, and C diets survived until 37, 39, and 37 days after hatching, respectively. However, the leptocephali fed the D diet survived for 60 days after hatching. The protein content of each diet was very similar, but the n-3 HUFA concentration in the D diet was approximately twice as high as that of the others.

본 연구에서는 BFT (biofloc technology) system 수조로부터 분리된 미생물(Bacillus sp.)을 이용하여 Marine snow와 유사한 유기물 분해산물을 만들어 뱀장어 자어먹이로 활용 가능성을 조사하였다. 유기원으로는 계란, 참다랑어, 뱀장어, 담치, 갯지렁이, 멍게, 바지락 그리고 새우를 이용하여 8 종류의 유기물 분해산물(HE, TM, EM, PC, TA, MS, HA, SP)를 생산했다. 생산된 유기물 분해산물은 특정한 형태는 나타나지 않았으며, 크기도 $10-20{\mu}m$의 미세한 것부터 $100{\mu}m$ 이상 되는 것까지 다양하였다. 부화 후 20일부터 다양한 유기물 분해산물을 이용하여 제조한 4 종류의 먹이(A, B, C, D-type)를 급이한 결과 A, B, C-type의 먹이를 급이한 뱀장어 유생은 각각 부화 후 37일, 39일, 37일까지 생존하였으나, D-type의 먹이를 급히한 뱀장어 유생은 부화 후 60일 동안 생존하였다. 각 먹이의 단백질 함량은 비슷하였지만, D-type 먹이의 n-3 HUFA 농도는 다른 type의 n-3 HUFA 농도보다 약 2배 높았다.

Fig. 1. Artificial organic decomposition products formed by fermented organic particles by microbial strain Bacillus sp.

Fig. 2. Photographs of leptocephalus larvae fed each feed type shown in Table 1. Photographs A, B, C, and D show larvae fed each type of feed (feed type A, B, C, and D) listed in Table 1. Photograph E shows larvae fed dogfish shark egg yolk-based feed received from the Nationcal Institute of Fisheries Science.

Fig. 3. Changes in survival rates of leptocephalus fed each diet (A, B, C, D-type and dogfish shark egg yolk-based diet) shown in Table 1 and from day 20 after hatching.

Fig. 4. Changes in body length of leptocephalus each diet (A, B, C, D-type and dogfish shark egg yolk-based diet) shown in Table 1 from day 20 after hatching.

Table 1. Feed formulation table for investigating the survival effect of diets on leptocephalus larvae of eel (A. japonica) from day 20 after hatching

Table 2. Amino acid content and protein concentration of each diet listed in Table 1

Table 3. Fatty acid content of each diet listed in Table 1