So went the joke-line from Finding Nemo's regal blue tang fish Dory: "I suffer from short term memory loss, it runs in my family… at least I think it does."

Now, a new study doesn't just challenge that old cliche about fish having poor memory - but suggests they have capacity to pass information down through generations.

At the centre of their new findings is what's called DNA methylation – a process that encodes additional information across generations, and which scientists are only just beginning to understand.

DNA is often compared to a large book, with the words representing an instruction manual for life, while DNA methylation might be likened to leaving handwritten notes in the margins of the book saying which pages are the most important, or recording newly acquired information.

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In humans, these notes are removed at each generation but this apparently does not occur in fish.

"Methylation sits on top of DNA and is used to control which genes are turned on and off," said the study's first author, University of Otago anatomy PhD student Oscar Ortega.

It also helped to define cellular identity and function, he added.

"In humans and other mammals, DNA methylation is erased at each generation; however, we found that global erasure of DNA methylation memory does not occur at all in the fish we studied."

In recent years, much attention has been paid to the idea that significant events such as war or famine can have a lasting effect on subsequent generations through the inheritance of altered DNA methylation patterns.

While these "trans-generational" DNA memory effects appeared to be potentially important, because of DNA methylation erasure events during development, it is thought to be extremely rare in humans.

However, because fish apparently did not have these erasure events, it seems possible they can transmit life experience through their DNA in the form of methylation.

Dr Tim Hore, research team leader and Senior Lecturer, at Otago's Department of Anatomy, said the study's findings provide new avenues for scientists to study how the memory of events in one generation, can be passed on to the next.

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Cells transmitting information to the next generation in fish (highlighted green) do not erase memory attached to DNA as humans do. Photo / University of Otago
Cells transmitting information to the next generation in fish (highlighted green) do not erase memory attached to DNA as humans do. Photo / University of Otago

"Mammalian biologists have searched long and hard to find reliable examples of where altered DNA methylation patterns are passed on to subsequent generations; yet only a handful have been verified in repeated studies," Hore said.

"However, unlike humans, DNA methylation is not erased at each generation in at least some fish.

"So, we think intergenerational memory transfer through DNA methylation could be much more common in fish."

The researchers hope this new knowledge into DNA methylation inheritance will drive new understanding into what molecular secrets are passed from parents to their offspring, ultimately, rewriting the book of life as we know it.

The findings have been published in the journal Nature Communications.