METHOD FOR REDUCING BACTERIAL CONTAMINATION IN AN AQUACULTURE

Abstract: In the method according to the invention live food organisms for aquaculture, such as rotifers and in particular Artemia, are treated with a bactericidal isothiazolin derivative to suppress bacterial contamination. The isothiazolin derivative is preferably a derivative of 4-isothiazolin-3-one, in particular 5-chloro-2-methyl-4-isothiazolin-3-one and/or 2-methyl-4-isothiazolin-3-one. It can be added as such to the growing media of the food organisms or be coated onto cysts of the organisms and/or included in an enrichment product for preparing an enrichment medium. The invention also relates to cysts of live food organisms coated with the bactericidal isothiazolin derivative and to enrichment products containing such derivative.

Description: "Method for reducing bacterial contamination in an qqiiacmfoire" The present invention relates to a method for reducing bacterial contamination as a result of the addition of live food organisms in an aguaculture by treating these latter food organisms with a bactericide. In practice, use is made for example of rotifers and subsequently of Artemia nauplii as live food organisms for aquaculture, more particularly as live food in early marine larval rearing. It is known that especially these Artemia nauplii are in practice heavily contaminated with bacteria which bloom during the hatching process and can reach numbers of more than 10 7 /g wet weight. As this bacterial flora consists mainly of Vibrio sp., potential fish/shrimp pathogens, Artemia nauplii can be considered as a possible carrier of pathogenic bacteria which can cause disease/mortality outbreaks in larval rearing, especially when the larvae are stressed. Several studies have been carried out to reduce this bacterial load with chemotherapeutics, in particular with antibiotics. However, the use of antibiotics should be avoided due to the risks for bacterial resistance. Other, broad-spectrum chemotherapeutics, on the other hand, such as for example chlorine dioxide, were found to be very harmful for the live food organisms themselves. An object of the present invention is therefore to provide a new method wherein the bacterial contamination can be effectively reduced without hampe¬ ring the growth of the food organisms. To this end, the method according to the invention is characterized in that said live food organisms are treated with a bactericidal isothiazolin derivative. It has been found that the use of a bactericidal isothiazolin derivative allows to achieve a significant reduction of bacterial numbers, especially of Vibrio sp. , without negative effects on the food organism. The intended isothiazolin derivatives are already known per se as biocides used for example in breweries for disinfecting ducts, etc. As to compounds included in this class of bactericidal isothiazolin derivatives, reference is made to GB-A-1,224,661 ; US-A- 3,523,121 ; US-A-3,761,488 and US-A-4,150,026 which are included herein by way of reference. The isothiazolin derivative is preferably a derivative of 4-isothiazolin-3-one. The invention further relates to cysts of live food organisms for aquaculture treated with a bactericide. According to the invention, said cysts, in particular Artemia cysts, are coated with a bactericidal isothiazolin derivative. The invention also relates to an enrich- ent product for preparing an enrichment medium for live food organisms for an aquaculture. This enrichment product is characterized in that it comprises a bacteri¬ cidal isothiazolin derivative in an effective amount to reduce bacterial growth in said enrichment medium. Further advantages and particularities of the present invention will become apparent from the following description of some particular embodiments of the method, the cysts and the enrichment product accor¬ ding to the invention. The method according to the present invention is intended to suppress bacterial contaminati- on in aquaculture by reducing the number of bacteria associated with the live food organisms. These live food organisms are for example rotifers and Artemia but also other live food organisms can be considered. In the following part, reference will be especially made to Artemia. The live food organisms can be used for different kinds of aquacultures, in particular for the culture of Crustaceae, Mollusca and fish. According to the invention, the live food organisms are treated with a bactericidal isothiazolin derivative. These isothiazolin derivatives are already known per se. For the particular application of the present invention, a selection should be made on the basis of the effectiveness against the bacteria associa- ted with the live food organisms and their possible effects on these latter organisms. A preferred class of bactericidal isothia¬ zolin derivatives are the 4-isothiazolin-3-one derivati¬ ves. A particular preference is given to 5-chloro-2- methyl-4-isothiazolin-3-one, 2-methyl-4-isothiazolin-3- one or a combination of these two compounds. It is also possible to use the isothiazolin derivatives as metal salt complexes described for example in US-A- 4,150,026. When used as live food organism for aquaculture, Artemia is put on the market as cysts. These cysts are hatched in a hatching medium, for example in seawater at 28°C for about 24 hours, and are usually subsequently further enriched with vitamins, fatty acids, etc. in an enrichment medium, also for about 24 hours. The enriched Artemia nauplii can then be used as live food organisms for aquaculture. In the method according to a particular embodiment of the invention, an effective concentration of the isothiazolin derivative is provided in the grow media, i.e. in the hatching medium and if used in the enrichment medium, to reduce bacterial growth therein. Indeed, it has been observed that bacteria, including possibly pathogenic bacteria such as Vibrio sp., develop well in these media. To suppress bacterial contamination in the hatching medium, the bactericidal isothiazolin deriva¬ tive can be added directly thereto. However, in a preferred embodiment the isothiazolin derivative is adhered to the Artemia cysts in an amount to achieve the required effective concen¬ tration in the hatching medium. In this respect, it has been found that cysts submitted to such a disinfection procedure can be stored for several months without any negative effects on the hatching efficiency and antibacterial activity. To suppress bacterial contamination in the enrichment medium, if such a medium is used, the live food organisms are preferably first of all washed. According to the invention, a bactericidal isothiazolin derivative is further added to the enrichment medium, also in an effective amount to reduce bacterial growth therein. In a preferred embodiment, the bactericidal isothiazolin derivative is included in an enrichment product for preparing the enrichment medium. Such an enrichment product contains for example vitamins and fatty acids and may in particular be in the form of a concentrated emulsion. An example thereof is the commercial enrichment emulsion SuperSelco from Artemia Systems S.A., Belgium. In both growing media, i.e. in the hatch¬ ing and in the enrichment medium, the isothiazolin derivative is preferably added until a concentration between 1 and 7 ppm is achieved. This concentration is more particularly comprised between 1.5 and 4 ppm and good results have been obtained with a concentration of about 2 ppm. In case of rotifers, it may however be necessary to use much lower concentrations. The following example illustrates the effects on the bacterial contamination of live food organisms which can be obtained by the method according to the present invention, and in particular by using cysts and an enrichment product according to the inven¬ tion. Example 1000 g Artemia cysts (GSL-strain) where coated with 7.5 g Pastosept available from S.A. SOPURA N.V. and containing a mixture of 5-chloro-2-methyl-4- isothiazolin-3-one (10.4%) and 2-methyl-4-isothiazolin- 3-one (3.5%). After drying to a humidity content of 5- 8%, the cysts were vacuum packed and stored at 4°C. A same batch of cysts was kept as a control. At different time intervals, i.e. after 2, 4, 8 and 12 weeks respectively, both the treated and control cysts were hatched in standard conditions, i.e. for 24 hours in seawater at 28°C. Two grams of cysts were added more particularly into 1 1 of seawater. After 24 hours the nauplii were harvested and samples of the hatching medium and the rinsed nauplii were taken for determination of the total count on Marine agar (MA, Difco) , and Vibrio sp. on TCBS (Oxoid) . The hatching efficiency (number of nauplii/g) was also determined. To test the antibacterial activity during enrichment, hatched nauplii of the disinfected and the control group were transferred to an enrichment tank and enriched with the commercial enrichment emulsion SuperSelco (Artemia Systems S.A. , Belgium) . The treated Selco contained 30 g/1 Pastosept and was diluted 2000 times to achieve the enrichment medium. After 24 hours the nauplii were rinsed and samples were taken for bacteriological and lipid analyses. Table 1 Number of CFU/g or /ml on MA 1 and TCBS 2 after 24h incuba¬ tion of Artemia cysts, (control and treated) and after 24h enrichment with SuperSelco (control and treated) . Treatment HA TCBS hatching control (N) 3 10* 10 7 hatching control (HW) 4 10 7 10 6 hatching disinfected (N) 10 4 10 3 hatching disinfected (HW) 10 3 10 2 enrichment control (N) 10 8 10 8 enrichment control (EW) 3 10 7 10 7 enrichment disinfected (N) 10 5 10 4 enrichment disinfected (EW) 10 3 10 3 1 : Marine Agar - general medium for growth of marine bacteria 2 : TCBS - specific medium for growth of Vibrio sp. 3 : N = numbers expressed in CFU/g nauplii 4 : HW = numbers expressed in CFU/ml hatching water 5 : EW = numbers expressed in CFU/ml enrichment water Artemia cysts, submitted to the disinfec¬ tion procedure hatched into much less contaminated nauplii compared to the control nauplii. After 24h the control nauplii contained up to 10 6 -10 7 bacteria/g, while on the disinfected nauplii the total number was reduced to 10 3 -10 4 bacteria/g. The reduction in Vibrio sp. was even more drastic (table 1) . This difference is also clearly visible in the hatching water : the hatching water after 24h hatching has a certain turbidity due to the bacterial growth, the water is completely clear when the disin¬ fection was applied. When the evolution of bacterial numbers in function of time is considered, it is clear that during a storage of 3 months at 4°C no big changes in numbers occur. The antibacterial activity is still present after that period as can be seen in Figure l. This figure shows the evolution of bacterial numbers in function of treatment and storage period at 4°C. There is no significant difference in hatching efficiency between control and disinfected cysts. When the disin¬ fection procedure is also applied during enrichment, a similar reduction in bacterial numbers is observed. Still a reduction with a factor 100 to 1000 is obtained on the nauplii after 24h enrichment (table l) . The difference is even more pronounced in the enrichment water. This leads to a much "cleaner" enrichment without slime formation on the tank walls. Lipid analyses revealed that enrichment levels with highly unsaturated fatty acids were the same in both treated and control Artemia. From this example it can be concluded that the use of a disinfection pro¬ cedure during hatching and enrichment of Artemia leads to a significantly lower bacterial contamination (especially Vibrio sp.) of the nauplii. This means that the chances of transfer of potential fish pathogens via the live food to the predator is also reduced. Cysts submitted to this disinfection procedure can be stored for several months without any negative effects on hatching efficiency and antibacterial activity. In a preliminary feeding experiment with seabass larvae the effect of feeding the disinfected Artemia was evaluated using survival, growth and stress resistance as criteria. No negative effects could be demonstrated. It is clear that the invention is not limited to the above described embodiments but that several modifications can be applied thereto without leaving the scope of the present invention. In this respect, it should be noted that in some cases, it may be preferable to add the bactericidal isothiazolin derivative only to the enrich¬ ment medium, thus without coating the Artemia cysts therewith.

Claims: CLAIMS 1. A method for reducing bacterial contamination as a result of the addition of live food organisms in an aquaculture by treating these latter food organisms with a bactericide, characterized in that said live food organisms are treated with a bactericidal isothiazolin derivative. 2. A method according to claim 1, charac¬ terized in that said live food organisms are cultivated in a growing medium in the presence of said bactericidal isothiazolin derivative in an effective concentration to reduce bacterial growth therein before being added to said aquaculture. 3. A method according to claim 2, charac- terized in that said live food organisms are grown from cysts in a hatching medium to which said bactericidal isothiazolin derivative is added. 4. A method according to claim 3, charac¬ terized in that said isothiazolin derivative is adhered to said cysts in an amount to achieve said effective dose in the hatching medium.. 5. A method according to claim 2 or 3, characterized in that said effective dose is comprised between 1 and 7 ppm, and comprises preferably 1.5 to 4 ppm, and more particularly about 2 ppm. 6. A method according to any one of the claims 2 to 5, characterized in that said live food organisms are further enriched in an enrichment medium to which said bactericidal isothiazolin derivative is added in an effective amount to reduce bacterial growth in this enrichment medium. 7. A method according to claim 6, charac¬ terized in that said bactericidal isothiazolin deriva¬ tive is included in an enrichment product for preparing said enrichment medium. 8. A method according to any one of the claims 1 to 7, characterized in that said isothiazolin derivative is a derivative of 4-isothiazolin-3-one. 9. A method according to claim 8, charac- terized in that said isothiazolin derivative comprises 5-chloro-2-methyl-4-isothiazolin-3-one and/or 2-methyl- 4-isothiazolin-3-one. 10. Cysts of live food organisms for aquaculture treated with a bactericide, characterized in that said cysts are coated with a bactericidal isothia¬ zolin derivative. 11. Cysts according to claim 10, charac¬ terized in that said cysts are Artemia cysts. 12. Cysts according to claim 10 or 11, characterized in that said cysts are coated with an effective amount of said isothiazolin derivative to achieve an effective concentration thereof in the hatching medium to reduce bacterial growth therein. 13. An enrichment product for preparing an enrichment medium for live food organisms for an aquaculture, characterized in that said enrichment product comprises a bactericidal isothiazolin derivative in an effective amount to reduce bacterial growth in said enrichment medium.

Inventors: DEHASQUE MARLEEN, DEVRESSE BERNARD, LEGER PHILIPPE, SORGELOOS PATRICK, DEHASQUE, MARLEEN, DEVRESSE, BERNARD, LEGER, PHILIPPE, SORGELOOS, PATRICK
Applicants: DEHASQUE MARLEEN, DEVRESSE BERNARD, INVE AQUACULTURE NV, LEGER PHILIPPE, SORGELOOS PATRICK, DEHASQUE, MARLEEN, DEVRESSE, BERNARD, INVE AQUACULTURE N.V., LEGER, PHILIPPE, SORGELOOS, PATRICK
Application year: 1995
Main classification: A01N43
IPC codes: A01N43, A23K1, A61K31