Collecting and identifying fish

Article | Updated 4 months ago

Curators at the Western Australian Museum are regularly involved in scientific projects that aim to increase our understanding of Western Australian biodiversity and biogeography. In this podcast Curator of Fishes Dr Glenn Moore explains the methods used to collect fishes in order to survey as much of the biodiversity as possible, and his approach to identifying species.

 

Image of the skeletal structure of a fish

Cleared and stained leatherjacket – Fish specimen that has undergone a chemical treatment called ‘clear and stain’. This method makes it possible to see through fishes and to study their skeletons without dissecting specimens
Image copyright WA Museum 

Transcript

The first thing is knowing where we are going and that determines how we collect. Then that determines how we prepare for the field trip, so if we are doing marine type work – it’s mostly diving, so we will spend a lot of time underwater so we need to get out all that dive gear and all that stuff, sorted, that’s probably the biggest part and of course they is a lot of health and safe issues. We also then have to decide how many things we want to collect and how we might collect them, so we use a variety of methods of collecting by hand, by fishing, chemicals, we use chemicals to anesthetise the fish, or to knock them out.

We collect what we need, so mostly what we collecting we’re collecting to keep in the collection, the State’s collection. So usually if we collect (we plan to keep it). When we are fishing it’s a bit different, because you don’t know what you are going to get. So when we are fishing we’ll often just get things (and) we might take a tissue, take a bit of a fin, a clip of the fin for tissue, take some photos and maybe some measurement and then release them.

When we are underwater we will usually see a range of reef fish and all that sort of fish, like that swimming in an aquarium but you don’t see the big things: the tuna, and the mackerel, and the marlin and whatever else is around. You don’t often see them when you are diving, you sometimes do but you don’t see them all the time. So we fish as well and that allows us to sample a group of fish that we don’t normally see while we are underwater. So that is the idea, we try and use a range of methods so that we capture as much of the biodiversity that’s in the area as possible.

We use a lot of visual census, so we do what’s called UVC – Underwater Visual Census – and we basically just swim a transect and just count and write down absolutely everything we see. That is a very common approach that we do,  of course that means you need to know the fish very well because you don’t catch them in your hand, so that’s quite challenging, especially when we are working in the Kimberley where there is one and a half thousands species of fish known, it’s a big job. I would say that I know the vast majority of them but there are definitely things that we don’t know, and that the things that we don’t know that we usually then try to collect and then we can try and figure them out. We might take photo as well if we can’t catch it, but sometimes they are hard to catch, but if we can catch them then we try to catch them and that way we can identify them properly.

First of all we sort them out, which is a bit of a process – depending on the method that we used to catch them, so if we use one of the chemicals for example we might get a whole lot of fish so we need to go through them. For the most part we take some samples of them, we take little piece of tissue from them, so we can store that for doing DNA work, and that’s important for a couple of reasons: one is it’s a useful tool, actually a really important tool now to try and identify different species, but secondly it’s also really useful to look at what’s called connectivity which is how different parts of the reef are connected to other parts, so how the fish that live on this reef are related to the fish that live on that reef, or fish that live in Indonesia or in Queensland, or whatever, so we can start look at differences in populations, and then we can overlay the morphological things that we can measure as well, so you know scales, and fins, and all those sorts of things.

With fish what else do we do? We do morphometrics, it’s called, so that’s relative measurements, so you know, how deep the body is compared to how long it is, or how long the fins are relative to the body, how big the eye is, these sort of shape things, and it’s usually proportional. And sometimes the skeleton is really important, so the number of vertebrae they have, or the structure of the bones in certain parts of the jaw or in the fins - things like that as well, so we use X-Rays for that. You can also do clearing and staining which is a method that turns all the flesh – it uses an enzyme to turn all the flesh clear and then you stain all the bones with a bright coloured stain and then you can basically see through the fish.