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Substance essential for metamorphosis of fish larvae extracted from Artemia
Aquaculture, 27 (1982) 83-85 Elsevier Scientific Publishing Company, Amsterdam -
83
Printed in The Netherlands
Short Communication SUBSTANCE EXTRACTED
ESSENTIAL FOR METAMORPHOSIS FROM ARTEMIA
OF FISH LARVAE
J. FLUCHTER Bayetische Landesanstalt fiir Fischerei, Republic of Germany) (Accepted
Weilheimerstr. 8a, 8130 Starnberg (Federal
12 June 1981)
ABSTRACT Fliichter, J., 1982. Substance essential for metamorphosis Artemia. Aquaculture, 27: 83-85.
of fish larvae extracted
from
Up to now the larval stages of fishes could not be reared successfully past metamorphosis when fed exclusively upon dry food. In rearing whitefish larvae, living Artemia nauplii could be replaced by shock-frozen ones (at -196°C). This suggested that a substance essential for the whitefish larvae is present in living Artemia and preserved during rapid shock freezing. This substance seemed to be insoluble in water. It could be dissolved and extracted from the nauplii by acetone and could be transferred to a dry food. This enriched dry food offered to the whitefish larvae enabled them to grow up to and past metamorphosis successfully.
In recent years it has often been reported that the larval stages of different fish have an essential requirement for a special kind of living food up to metamorphosis. In rearing whitefish larvae, natural zooplankton can be replaced by the nauplii of the brine shrimp, Artemia salina. Larvae have not yet been succesfully reared on dry food or even on slowly frozen Artemia, but Artemiu nauplii shock-frozen in liquid nitrogen (at -196°C) were found to be as acceptable as living ones and enabled the larvae to metamorphose. This suggests that there is an essential substance to be found in living Artemiu nauplii which is connected with intermediary metabolism and so it may be absorbed by enzymatic action that does not immediately stop during slow freezing. That would explain why this essential substance is preserved when Artemiu is rapidly shock-frozen. This substance, which initially was only hypothetical, must be largely insoluble in water, because the nauplii of Artemiu burst during shock-freezing due to the expansion of the water in the body tissue. If the substance were water-soluble it would be washed off during feeding. This substance might be soluble in a solvent other than water and so may be extractable from the shock-frozen Artemiu nauplii and used to enrich a diet for fish larvae. 0044-8486/82/0000-0000/$02.75
o 1982 Elsevier Scientific Publishing Company
84
To test this hypothesis a basic diet is required, consisting of a dry food which is acceptable to the fish larvae and contains all nutrients, vitamins, etc. which are known up to now to be essential for fish nutrition. Larvit A (Trouw Co., Putten, The Netherlands) was found to fulfill these criteria. It was at first taken up voraciously by the whitefish larvae, and initially good growth and low mortality could be observed. However, the larvae could not survive past metamorphosis. An attempt was next made to separate the factor preserved in the shock-frozen Artemia nauplii by dissolving it in a special solvent and so removing it from the nauplii by filtration. This separation would allow enrichment of the dry food and so enable the whitefish larvae to get past metamorphosis when fed on the supplemented dry food. Several experiments were carried out and the following method was found to be successful: to 25 g shock-frozen Artemia nauplii (wet weight) 100 ml acetone were added, stirred for one hour, and left untouched for one night. Then the extract was separated by filtration and added to 30 g Larvit A. Acetone was removed by vacuum of ca. 70 mm Hg for 10 h as well as possible, and then the “cake” was powdered again and offered to the whitefish larvae. Although the results of the feeding experiments (Table I) are not yet fully evaluated, it can be stated that, after 42 days feeding, the whitefish larvae fed on the dry food Larvit supplemented with acetone extract from Artemia nauplii metamorphosed without difficulty. They grew as well as those fed on living Artemiu. Their survival rate was remarkably higher than the control fed upon living Artemia and appreciably higher than the control fed upon shock-frozen Artemiu. Though the rearing conditions were not ideal (as the high mortality of the control fed on living Artemiu indicates), the survival rate demonstrated that the factor essential for TABLE
I
Success of feeding whitefish larvae on an enriched dry food Food
Survivors (%I
Average length (mm)
Metamorphosed
Larvit A
10
16
none
Larvit A + acetone extract of Artemia
48
23
all
21
23
all
14
20
all
Living Artemia nauplii Shock-frozen Artemia
85
metamorphosis of the larvae was dissolved from Artemiu and was transferred to the dry food. Moreover, the larvae showed marked vitality. This provisional result cannot yet clear up the question of whether this factor isolated from Artemiu nauplii but up to now identified only biologically as essential for metamorphosis of whitefish larvae is a single chemical compound or a complex of several substances. The biochemical identification of this essential factor will be the important step to developing a synthetic exclusive larval food to replace Artemiu nauplii when rearing fish larvae.
83
Printed in The Netherlands
Short Communication SUBSTANCE EXTRACTED
ESSENTIAL FOR METAMORPHOSIS FROM ARTEMIA
OF FISH LARVAE
J. FLUCHTER Bayetische Landesanstalt fiir Fischerei, Republic of Germany) (Accepted
Weilheimerstr. 8a, 8130 Starnberg (Federal
12 June 1981)
ABSTRACT Fliichter, J., 1982. Substance essential for metamorphosis Artemia. Aquaculture, 27: 83-85.
of fish larvae extracted
from
Up to now the larval stages of fishes could not be reared successfully past metamorphosis when fed exclusively upon dry food. In rearing whitefish larvae, living Artemia nauplii could be replaced by shock-frozen ones (at -196°C). This suggested that a substance essential for the whitefish larvae is present in living Artemia and preserved during rapid shock freezing. This substance seemed to be insoluble in water. It could be dissolved and extracted from the nauplii by acetone and could be transferred to a dry food. This enriched dry food offered to the whitefish larvae enabled them to grow up to and past metamorphosis successfully.
In recent years it has often been reported that the larval stages of different fish have an essential requirement for a special kind of living food up to metamorphosis. In rearing whitefish larvae, natural zooplankton can be replaced by the nauplii of the brine shrimp, Artemia salina. Larvae have not yet been succesfully reared on dry food or even on slowly frozen Artemia, but Artemiu nauplii shock-frozen in liquid nitrogen (at -196°C) were found to be as acceptable as living ones and enabled the larvae to metamorphose. This suggests that there is an essential substance to be found in living Artemiu nauplii which is connected with intermediary metabolism and so it may be absorbed by enzymatic action that does not immediately stop during slow freezing. That would explain why this essential substance is preserved when Artemiu is rapidly shock-frozen. This substance, which initially was only hypothetical, must be largely insoluble in water, because the nauplii of Artemiu burst during shock-freezing due to the expansion of the water in the body tissue. If the substance were water-soluble it would be washed off during feeding. This substance might be soluble in a solvent other than water and so may be extractable from the shock-frozen Artemiu nauplii and used to enrich a diet for fish larvae. 0044-8486/82/0000-0000/$02.75
o 1982 Elsevier Scientific Publishing Company
84
To test this hypothesis a basic diet is required, consisting of a dry food which is acceptable to the fish larvae and contains all nutrients, vitamins, etc. which are known up to now to be essential for fish nutrition. Larvit A (Trouw Co., Putten, The Netherlands) was found to fulfill these criteria. It was at first taken up voraciously by the whitefish larvae, and initially good growth and low mortality could be observed. However, the larvae could not survive past metamorphosis. An attempt was next made to separate the factor preserved in the shock-frozen Artemia nauplii by dissolving it in a special solvent and so removing it from the nauplii by filtration. This separation would allow enrichment of the dry food and so enable the whitefish larvae to get past metamorphosis when fed on the supplemented dry food. Several experiments were carried out and the following method was found to be successful: to 25 g shock-frozen Artemia nauplii (wet weight) 100 ml acetone were added, stirred for one hour, and left untouched for one night. Then the extract was separated by filtration and added to 30 g Larvit A. Acetone was removed by vacuum of ca. 70 mm Hg for 10 h as well as possible, and then the “cake” was powdered again and offered to the whitefish larvae. Although the results of the feeding experiments (Table I) are not yet fully evaluated, it can be stated that, after 42 days feeding, the whitefish larvae fed on the dry food Larvit supplemented with acetone extract from Artemia nauplii metamorphosed without difficulty. They grew as well as those fed on living Artemiu. Their survival rate was remarkably higher than the control fed upon living Artemia and appreciably higher than the control fed upon shock-frozen Artemiu. Though the rearing conditions were not ideal (as the high mortality of the control fed on living Artemiu indicates), the survival rate demonstrated that the factor essential for TABLE
I
Success of feeding whitefish larvae on an enriched dry food Food
Survivors (%I
Average length (mm)
Metamorphosed
Larvit A
10
16
none
Larvit A + acetone extract of Artemia
48
23
all
21
23
all
14
20
all
Living Artemia nauplii Shock-frozen Artemia
85
metamorphosis of the larvae was dissolved from Artemiu and was transferred to the dry food. Moreover, the larvae showed marked vitality. This provisional result cannot yet clear up the question of whether this factor isolated from Artemiu nauplii but up to now identified only biologically as essential for metamorphosis of whitefish larvae is a single chemical compound or a complex of several substances. The biochemical identification of this essential factor will be the important step to developing a synthetic exclusive larval food to replace Artemiu nauplii when rearing fish larvae.