Techniques for microbial control in the intensive rearing of marine larvae

The intensive cultivation conditions for marine larvae may easily cause mic robial problems, resulting in poor growth and mass mortality, and technique s for improvement by enhancing environmental and larval factors should be d eveloped. Establishment of a beneficial, protective microflora of marine la rvae can be obtained by use of microbial matured water and probiotics. Micr obial maturation of the rearing water before use in the larval tanks, can b e obtained by running the water through a maturation unit that selects for non-opportunistic microflora. A diverse bacterial flora established by non- opportunists is believed to inhibit proliferation of opportunistic pathogen ic bacteria in the water and the larvae. When used in the earliest developm ental stages of marine fish larvae, enhanced growth and survival can be obt ained. Also, the introduction of probiotic bacteria may promote the defence of the gut flora against pathogenic bacteria. Probiotic bacteria can be ad ded directly to the water or administered to the larvae via live food, such as rotifers and Artemia. Further developments in these techniques are need ed for improved control of bacterial number, growth and colonisation in the larval gut, as well as the identification of bacteria with probiotic effec t on the host. Disinfection of eggs is a positive factor for control of gro wth and transfer of bacteria in larviculture. For marine fish eggs glutaral dehyde has suitable properties as a disinfectant, which improves hatching, development and survival of larvae. Because marine fish larvae have no spec ific immune system at hatching, non-specific defence is very important duri ng the first developmental stages, and suitable techniques for stimulation of the non-specific immune defence may become important in future marine la rval rearing. Enhanced viability of marine fish larvae and juveniles, has b een obtained by treatment with FMI, which is a mannuronic acid polymer. Rou tes of administration were either into the water or via live food. A techni que for incorporating immunostimulants in rotifers and Artemia for controll ed transfer of immunostimulants to marine larvae, is described. (C) 1999 El sevier Science B.V. All rights reserved.