There are many types of fish in the world that have different appearances, different behaviors, and live in different habitats. So the initial discussion focused around what makes a fish a fish. While many people seem to think they know exactly what you are talking about when you say the word fish, sometimes it can be pretty challenging for them to give a simple definition of what a fish is. The students brainstormed a bit and came up with many of the important characteristics. In general, fishes have three important traits in common: 1) they live in water, 2) they have fins and 3) they use gills to get their oxygen from the water.
When it comes to identifying fish, it is also important to know that life is full of changes. Most fish go through a cycle where they start as an embryo (or fertilized egg), hatch into a larval form, develop into a juvenile form and finally mature into an adult form. Fish from the same species can look very different from each other depending on which of the forms you are trying to identify. For example, the picture below shows a larval (left) and adult (right) fish from the same species.
One fish, two fish, red fish, blue fish (Dr. Suess).
The students then worked through the classification system that most biologists and scientists use, and that many of them had already learned in school! This system is a method by which biologists group and categorize organisms by biological type, arranging organisms into a hierarchical series of nested groups. The scientific approach is to take all things and group them (from largest group to smallest group) by: Domain, Kingdom, Phylum, Class, Order, Family, Genus and Species (which usually has a related common name). The following questions helped CRFPO biologists and the students determine if what they were looking at could be a fish. To possibly be a fish, they needed to answer “Yes” to the following: 1) Does it have cells with a nucleus? (Domain = Eucaryota), 2) Is it a multicellular, heterotroph? (Kingdom = Animalia), 3) Does it have a hollow, dorsal nerve chord? (Phylum = Chordata). Within this Phylum there are three Classes of fish. Chrondrichthyes are the cartilaginous fish for which there are over 900 species. Agnatha are the jawless fish for which there are over 100 species. Osteichthyes are the bony fish for which there are over 30,000 species. The goal of FWS 101 was to focus on five particular species and be able to identify two jawless fish as well as three bony fish. The jawless fish were both from the Order Petromyzontiformes and Family Petromyzontidae and their common names were Pacific lamprey & western brook lamprey. The bony fish were all from the Order Salmoniformes and Family Salmonidae and their common names were Chinook salmon, coho salmon and cutthroat trout.
Its All In The Sequence?
CRFPO biologists then went through a series of questions to help determine which of these five species a student might be looking at.
Question 1) “Is it jawless or jawed”? The pictures below show a jawless fish (left) and jawed fish (right).
To be a lamprey a fish would have to be jawless. In addition, lamprey have gill slits, no paired fins and a notochord.
Question 2) Is it a Pacific lamprey or western brook lamprey?
If it was jawless, what does the caudal area look like? Two common species of lamprey in the Pacific Northwest are Pacific lamprey and western brook lamprey. The larval forms of these species can be difficult to identify (see the picture below). Larval Pacific lamprey (left) have a relatively light caudal ridge with a dark, uniformly pigmented caudal fin. Larval western brook lamprey (right) have a relatively dark caudal ridge with a clear, or speckled caudal fin.
Question 3) Is it a trout or a salmon?
Approximately 18 species of trout can be found world wide. Five of these species are found in the Pacific Northwest. Three of the species found in the Pacific Northwest are native (cutthroat trout, bull trout, rainbow trout) while two of the species have been introduced (brown trout and brook trout). Although trout and salmon can look somewhat similar, trout have less than 13 rays in their anal fin (while salmon have more than 12).
Question 4) Is it a cutthroat trout?
A trout is generally a cutthroat when it has red/pink marks (slashes) in the throat area, speckles on its body and dorsal fin, and teeth on its tongue.
Question 5) Is it a Chinook or a coho salmon?
Five species of salmon can generally be found in the Pacific Northwest (pink, chum, sockeye, Chinook and coho). In FWS 101, if the students identified a fish as a salmon, it could have been either a Chinook or coho salmon. Chinook salmon have parr marks that are wider than the spaces between them, an adipose fin with a clear center and no spots on dorsal fin. Coho salmon have parr marks that are oval and narrower than the spaces between them, anal and dorsal fins with leading edges that are white followed by black, an orange hue (mostly on adipose, anal and caudal fins) and no spots on the dorsal fin.
Every day, from here to there, funny things are everywhere (Dr. Suess).By the end of the day the students had done a tremendous job absorbing all of this information. They skillfully used the key below and had become experts identifying these five species of fish. And you never know when they might find one of these fish in their neighborhood stream!
FWS 101 - Dichotomous Fish Key (Abbreviated to help tell the difference between five species … Pacific lamprey, western brook lamprey, Chinook salmon, coho salmon, cutthroat trout).
1a. Fish is jawless (Petromyzontidae – lamprey) .................... 2
1b. Fish is bony with jaws (Salmonidae – salmon and trout) .................... 3
2a. Caudal ridge is lighter relative to surrounding areas; caudal fin is more pigmented relative to other species of lamprey …… Pacific lamprey – Entosphenus tridentata
2b. Caudal ridge has consistent dark pigmentation; caudal fin has relatively no pigmentation (clear) with some spotting possibly present .................... Western brook lamprey – Lampetra richardsoni
3a. Anal fin with 9-12 fin rays, dorsal fin speckled (trout) .................... 4
3b. Anal fin with 13-19 fin rays, dorsal fin not speckled (salmon) .................... 5
4. Red or pink streak on underside of each mandible; presence of basibranchial teeth .................... Cutthroat trout – Oncorhynchus clarkii
5a. Parr marks are wider than interspaces; adipose fin has clear center; no spots on dorsal fin .................... Chinook salmon – Oncorhynchus tschawytscha
5b. Parr marks are oval and more narrow than interspaces; leading edges of anal and dorsal fins have white followed by black; orange hue in adipose, anal, and caudal fins; no spots on dorsal fin .................... Coho salmon – Oncorhynchus kisutch
Submitted by Tim Whitesel, Jeff Jolley, Mike Hudson, and Courtney Newlon