a) eastern rainbowfish b) injecting a female rainbowfish with enriched stable isotopes, c) removing otoliths from a larval rainbowfish and d) otolith of a larval eastern rainbowfish after laser ablation mass spec.

All about rainbowfish

Eastern rainbowfish are one of the most numerically abundant fish in the wet tropics region of far north Queensland. Furthermore, they are hugely popular in the aquarium trade, due to their beautiful colours, and propensity to breed readily in captivity. However, we know little about their early life history, and this is partly due to having limited techniques available to study their biology and spatial ecology. Previous research as demonstrated that rainbowfish otoliths can tell us about age and growth, but an opportunity exists to examine if mass-marking of rainbowfish larvae is possible, via injections of enriched stable isotopes into adult female rainbowfish. If such a technique was effective, it would pave the way for future studies exploring the early life history ecology of this very important species.

This research was published in Marine and Freshwater Research. We also got the cover (see below)!

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Transgen marking

Removing otoliths from larval fish is painstaking work.

This study examined the effect of dosage of enriched stable isotopes on both offspring morphology, and marking efficacy. An important consideration is how long after an injection with isotopes does a female continue to produce marked offspring? Rainbowfish, being daily spawners, are an excellent model species to examine this question. By collecting eggs from females at regular intervals post-injection, it should be straightforward to work out the longevity of maternal transmission of enriched stable isotopes.

Transmission longevity

A mass spectrometry time trace of an otolith marked with Sr87. The Sr88/Sr87 ratio declines due to the increased abundance of Sr87

In this study I found that a female rainbowfish injected with a single dose of enriched stable isotopes can continue to produce marked larvae for at least 6 months post-injection. This is an exciting finding, as previous studies report longevity up to 3 months, and in some studies, considerably less. There is clearly an effect of dosage, with higher doses potentially having greater longevity. In the present study, I did not identify the time point in which all isotopes were depleted, but may be in the order of 10-12 months. This presents the opportunity to mass-mark the vast majority of a female's reproductive effort over her entire lifespan, with just a single injection.

Starrs, D., Ebner, B.C., Eggins, S.M., and C.J. Fulton (2014) Longevity in maternal transmission of isotopic marks in a tropical freshwater rainbowfish and the implications for offspring morphology. Marine and Freshwater Research 65: 400-408 doi: 10.1071/MF13150 LINK

Cover image of Marine and Freshwater Research, Volume 65, issue 5! Photo by B. Ebner