Tuesday, March 27, 2018

28/03/2018: Diving deeper for a sea lice solution

by Keith Filer, Ph.D. Research Project Manager for Aquaculture, Alltech

The small crustacean Lepeophtheirus salmonis, commonly referred to as sea lice, has a major impact on the production of Atlantic salmon (Salmo sala). Sea lice feed on fish skin, mucus and blood, with severe damage caused during high infestations. 


 
Lepophtheirus Salmonis,
commonly referred to as sea lice
Image credit: Alltech
Large rates of infestation lead to severe damage and possibly mortality due to the exposure of subcutaneous tissues, bacterial infections and stress. Various treatment options are available to reduce the impact of sea lice, but the treatments do result in increased mortality and reduced growth, as well as higher production costs. The estimated costs to the aquaculture industry due to sea lice are as high as US$1 billion annually. A combination of treatment and management strategies are commonly used to combat the impact of sea lice on salmon farms.

Conventional treatments

The treatments for sea lice control generally involve medicine administered through the feed, chemical baths and cleaner fish.

Maintaining low numbers of sea lice throughout a production cycle after transfer to sea can require all three treatments to be utilised. Medicated feed treatments are used for fish up to about two kilograms, with the cost being the prohibitive reason to not use it in larger fish.

Bath treatments can be incorporated into grading and transition periods with fish larger than two kilograms, but baths tend to be avoided with smaller fish because of the increased risk of mortality.

Cleaner fish such as wrasse are typically added to the pens with the smolt and remain in the pens throughout the entire production cycle. Treatments lose effectiveness as the salmon become larger than two kilograms.

Management strategies are also utilised to reduce the impact of sea lice and ensure that other treatment strategies are as effective as possible. An integrated pest management approach has been proposed in production areas with high incidence of sea lice. Such an approach could include stocking of single year classes, rotating production sites and coordinated treatment among farms in the same region. The industry in Norway has turned to mandatory and synchronised control efforts to reduce the impact of sea lice as much as possible.

A new approach
The active ingredients in the oral medications used to control sea lice move through the fish to the skin and into the sea lice once it has attached. With the skin and the associated mucus layer being the contact point for the sea lice, another approach is reducing the ability of the sea lice to attach to the skin. Critical to this approach is the innate immune response, which is an important component of fish health, and the epithelial and mucosal barrier, which are important because of the constant exposure to the environment. The mucus contains lectins, lysozymes, complement proteins, antimicrobial proteins and immunoglobulin M.

Information has been generated to suggest that a nutritional approach to the manipulation of the mucus layer, as well as the innate immune system in general, can reduce the incidence of ectoparasites on fish. These nutritional approaches have been used to increase the mucus layer in fish and supports additional innate immune responses. Alltech has used nutritional approaches with Bio-Mos® to support the innate immune response in a variety of fish species.

Bio-Mos consists of the complex carbohydrate mannan oligosaccharide that is derived from the yeast cell wall of a selected strain of Saccharomyces cerevisiae. Bio-Mos stimulates the natural defences of fish by optimisation of the immune function’.

Years of work with Bio-Mos led to the production of a soluble mannan-rich fraction (MRF). The soluble MRF can be used in very small quantities to maintain innate immunity responses of very young animals, even during development. The concept for the MRF was initially demonstrated in chicken eggs. Injection into the egg indicated that early life exposure optimised the innate immunity of the chicken throughout its growing period. Nutrigenomics was also used to identify changes in gene expression patterns when eggs were treated with the MRF.


Read the full article, HERE.

The Aquaculturists
This blog is maintained by The Aquaculturists staff and is supported by the
magazine International Aquafeed which is published by
Perendale Publishers Ltd

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