‘It is important that fish, as well as humans, get enough folate and other B vitamins before they breed. Deficiencies can have consequences for offspring, both regarding the number produced embryos and their health, says Kaja Helvik Skjærven, scientist at the National Institute of Nutrition and Seafood Research (NIFES). She is leading a study that examines how low B vitamin levels in feeds for zebrafish affects both the parents and the offspring.
Zebrafish is a vertebrate model species that is often used to study mechanism of embryonic development. The short life cycle and availability of good diagnostic tools makes this an excellent species to do investigative studies that can be of great relevance to the aquaculture industry.
Vegetable feed raw materials do not contain enough B vitamins
In order to sustain the growing demand of fish feed, more plant-based feed ingredients are used in the diets. Plant ingredients often contain less natural B vitamins and must therefore be supplemented to the diet. To ensure the welfare and health of the fish, it is essential that the right amount of various B vitamins are added.
‘The offspring of parents with B vitamin deficiencies were much less robust and could be more prone to diseases. The wrong nutrition of the parents at an early stage can have a domino effect on their offspring, changing the offspring’s development and health all the way to adulthood,’ says Skjærven.
Sixty percent fewer offspring and risk of disease
In the feeding trial, both male and female parents were given a diet containing slightly too little of the B vitamins folate, vitamin B12, vitamin B6 and the amino acid methionine. The scientists first found that the parents were shorter and weighed less than the fish in the control group. In addition, the composition of nutrients in their bodies had changed. They also found an effect on fecundity. Parents that received a diet with low levels of B vitamins produced 60 percent fewer offspring than the fish in the control group; they were less fertile.
When the scientists examined the offspring, they appeared to be visually fine, but had hidden deficiencies. Parents’ vitamin deficiencies affected the genetic expression in the embryo. Genes associated with infection and stress were higher expressed. Changes were also found in genes related to lipid transportation.
Cell division and gene regulation
‘Folate, vitamin B12, vitamin B6, and the amino acid methionine are very important in early embryonic development,’ says Skjærven.
These vitamins are important for many reasons including the rapid cell division that characterise early embryonic development. New DNA must be synthesised to complete cell divisions. The B vitamins are essential for the building blocks in the DNA, called nucleotides. Skjærven also explains that this is important for gene regulation, i.e. which genes are turned on or off in the offspring.
‘The parents’ nutrition thereby has a direct effect on the health of the offspring and their gene regulation. We are now studying how the offspring are doing as adults and we are initiating a bigger project in which a similar trial will be conducted on salmon. The study is funded by the Research Council of Norway and the purpose of the study is to investigate whether these mechanisms found in zebrafish can help to improve salmon health.
The scientific article: ‘Parental vitamin deficiency affects the embryonic gene expression of immune-, lipid transport- and apolipoprotein genes’ has been published in the international journal Scientific Reports.
The article is written as a collaboration between NIFES, Nord University and Rikshospitalet University Hospital OUS.