Effects of addition of 2 lactic acid bacteria on the development and conformation of sea bass larvae (Dicentrarchus labrax) and the influence on these microbiota

Developmental bone conformation problems such as spinal/skeletal deformities cause considerable issues for fish hatcheries. It is suspected that many of these deformities are caused by environmental, genetic or nutritional factors. Consequently it is important to research ways to limit development of these problems. Use of probiotics has been proposed as a possible means to reduce such deformities. Previous studies looking at use of lactic acid bacteria as a probiotic have shown that they are useful to reduce some causes of skeletal deformation in certain fish species. The mode of this interaction is not yet clearly understood and may be indirect but arise due to reduced numbers of pathogenic bacteria or reduction of inflammation of the larvae which may contribute to the risk of deformation. 

Lamari et al. (2013) aimed to study the effects of two strains of lactic acid bacteria; Pediococcus acidilactici and a strain of Lactobacillus casei on gene expression, associated microbiota and larval development. These strains of lactic acid bacteria were chosen because previous studies recommended that bacteria were chosen from the local environment or from the host to be used in the environment to improve potential for colonization. The bacteria were administered at 10⁶ and 10⁷ CFUs in two consecutive experiments. The 10 fold increase was decided on for the second experiment to boost the level of lactic acid above the detection threshold. There were three dietry groups; C which was the control, P had added Pediococcus acidilactici   and L had added Lactobacillus casei.

In both experiments growth of larvae was promoted by the addition of the bacteria but there was no significant difference in the number of spinal deformities between the control and experimental groups but significantly more spinal deformities were observed in group L than P.  Mineralization was delayed in group P but was overcome by most fish. Osteocalcin, a marker of ossification (the laying down of new bone material) was over expressed in group L. It can be concluded from these results that both types of bacteria influenced bone mineralization in different ways.

Counts of lactic acid bacteria remained low in both experiments therefore it can be inferred that dietary addition of the two strains of lactic acid bacteria does not lead to gut colonization. The fact that the dose was changed between the two experiments may be responsible for some of the differences observed between the experiments as dose is an important factor to consider when looking at the efficiency of probiotics.

This experiment confirmed use of Pediococcus acidilactici imporved skeletal conformation but the mode mode of action is still unclear. Ca conclusion cannot be made on the hypothesis of inflammation reduction because more observations and further work are needed to come to a conclusion.

Overall I found this paper quite interesting, it was easy to follow and I feel that its results form a basis for a lot of future work as it shows that probiotics are not only useful for growth but also some may have properties which may help to reduce skeletal bone deformation.

Lamari F, Castex M, Larcher T, Ledevin M, Mazura D, Bakhrouf A, Gatesoupe F. 2013. Comparison of the effects of the dietary addition of two lactic acid bacteria on the development and conformation of sea bass larvae, Dicentrarchus labrax, and the influence on associated microbiota.  Aquaculture 376-379; 137-145.