Fish in the Bay – January 2019, UC Davis Trawls – Parasite Paradise.

Field notes from the dark underbelly of the Bay:  Folks, I must do a short note about fish parasites.  This is off-topic and doesn’t quite fit into my regular “Fish in the Bay” narrative which is largely driven by a rosy-goggled (and mostly accurate) vision of a beautiful Bay filled with hundreds of species, from microbes to fish, birds, and harbor seals constantly cycling through endless interconnected life-processes.  The complete picture is even more complex, and not always so beautiful from a human point of view.

I occasionally see disturbing signs of fish parasites.  Any avid sports angler will tell you about them.  If you search “Fish Parasite” or similar words on YouTube you will find hundreds of videos even grosser than pimple popping. The whole truth must be told.

With that in mind, I assembled a rogue’s gallery of voracious parasites spotted during Hobbs trawls.

1. Copepod.

Parasitic copepod on a Northern Anchovy.

Caligidae Copepod, or “Sea Louse.”  This is a creepy bug.  I have seen a similar, but different-looking parasitic copepods on a brown smoothhound shark.  The above photo shows the copepod stuck to the side of an anchovy.  From left to right, you see the Copepod’s oral cone (or siphon), round shaped cephalothorax, and one of two egg-strings trailing behind (the other one probably broke off).

The term “Sea Louse” or “Fish Louse” is a very loose one.  As discussed below, numerous species of copepods and isopods are generically referred to as “lice.”  However, copepod parasites seem to get the most official recognition as “lice” of the marine world; here:, and here:

Copepod closeup after removal.

I scraped the bug off with my fingernail to get a better look. (Also, I always try to help a fish out when I can.)  The cephalothorax came off intact.  The oral cone kind of rolled into a ball of jelly though. 

When I showed this bug to Micah Bisson, he said, “Oh, that’s the one with a triangular shaped mouth that I saw in a presentation.”  I haven’t found the presentation, but this copepod’s mouth appeared triangular before I scraped her off.   

Another parasitic copepod on a Northern Anchovy.

Second copepod, different Anchovy.  Literature indicates that Caligidae Copepods can be very host specific.  I do not know if this particular variety infects any fishes other than Anchovies.

Two more copepod parasites.

Two Anchovies, Two different nasty copepod parasites!  All copepods shown are females with twin egg-strings trailing behind.  From what I read, males are much smaller and probably less conspicuous. 

Yet another revolting Caligidae Copepod parasite.  I could not see the oral cone on this one.  I have a suspicion that the soft oral cone projects out from the cephalothorax after the bug has latched on to the Anchovy.  I might have captured this copepod before she had a chance to really dig into her host. 

I could have further investigated these copepods this month, but frankly they are pretty gross, and that was all I could handle at the time.

2. Isopod.

Cymothoida Isopod

Cymothoida Isopod.  I first encountered this bug in November.  Jim Hobbs picked it out of the net and identified it as a likely gill parasite.  It is definitely Isopod of the Cymothoida suborder:

Cymothoida is a huge suborder of over 2,700 species!  Even the Bopyroidea parasites on Crangon discussed in the January Fish in the Bay report are part of this same suborder.

Isopod-Trilobite comparison

Cymothoida suborder, genus Lironeca.  Lironeca is my best guess for genus based on internet photos. 

My first reaction to many isopods is “Wow, they look like trilobites to me!”  This one resembles a trilobite even more than Synodotea.  Even so, I know that trilobites are long extinct and only remotely related.  Somehow, this segmented oval body-plan works so well in the marine environment that evolution favors it again and again.

My second reaction is, “What a pretty bug!”  I feel inclined to forgive her parasitic ways. (Larger Cymothoida-type isopods are females.) 

Strange but True:  Literature says that in many species of Cymothoida, the bug is born male. The younger male seeks a fish already hosting a bigger female Cymothoida.  The female broods a batch of young then dies.  Then not much later, after another molt or two, the male becomes female and waits for a new boyfriend!  If a male never finds a female, he will eventually turn into a female in any case.

Isopod parasite on a Longfin Smelt

Cymothoida isopod walking across the face of a Longfin Smelt.  I did not see this tiny Cymothoida in the photos until later when I got home.   The bug appears to have emerged from under the operculum (gill cover) as I was holding the fish.  Look closely to see the lost little bug as it wonders from fish gill cover to snout.

This was first proof-positive that Cymothoida infect Longfins!  (Important scientific knowledge – first for me anyway.)

Two different Cymothoida from Station Alv2.  These two bugs were a little smaller and had no distinct “nose” segment compared to the first big bug shown far above.  I presume these were younger bugs.  The “nose” segment may appear after additional molts, but I am only guessing. For all I know, these could be a different related species.

The third bug from station Alv2 was not noticed until I looked at the photo at home:  Yet another sneaky little Cymothoida was crawling under the chin of a Longfin Smelt!  The longfin looks to be “Young of Year” and therefore may not have migrated out of the Bay yet.  Until now, I assumed that Cymothoida live in coastal waters and arrive in Lower South Bay as hitchhikers.  Now, I suspect that some may live their full life-cycle inside the Bay.

Another Cymothoida found crawling on an American Shad.  This is another young one.  But, the eyes are wide-spaced compared to the youngsters shown further above.  Are these different species?  Or, just different age appearances? 

Cymothoida Isopods on YouTube:

Very similar isopod from the gills of a perch in the Chesapeake:   Everyone tends to identify these as Cymothoa exigua, because that one is the well-known “Tongue-eating Louse.”

Cymothoa exigua is discussed in detail here: 

Isopod, male, female, and babies from a Lingcod: 

Some tilapia heavily infested by gill parasites:  

This video shows isopods on an Alligator Gar starting at the 3:30 mark.  The isopods shown in the video are larger. I presume they are a freshwater species that latches onto the side of the fish. 

This video shows a different type of Cymothoa, (Again wrongly identified as Cymotha exigua (sic)), under crab carapices  This isopod variety looks more like Bopyroidea isopods I found on Crangon shrimp in January.

3. A Virus … or something.

Cauliflower lumps on the side of English Sole.

English Sole.  We are now catching young English Sole.  These come in from the ocean to feed and grow as cold rainwater flushes the rivers.  But, as seen last year, a plurality, if not a majority of Sole display awful looking skin lesions.  Both Dr. Hobbs and general literature confirm that English Sole are susceptible to more parasites than most fish.  I am going to say, these cauliflower-looking warts look like cases of Lymophocystis virus: 

More English Sole.  Two showing cauliflower warts.
English Sole with reddish warty protrusion near tail.

This English Sole has a reddish protrusion near the tail.  So many English Sole abnormalities look like cancer, but I am sure these result from parasites.

English Sole, and result of excisional biopsy (inset).

This Sole had defined welt on its side (bottom side in the photo).  I scraped it off hoping to find yet another one of the 2,500 Cymothoid isopod varieties.  What I found was yet another unidentifiable gelatinous mass.  There may be an isopod in there, but I didn’t feel motivated enough to continue the investigation.

A Howard et al. (2018) paper explores nematode (roundworm) parasite trends in Puget Sound English Sole:  The nematode causes bumps and welts on the bottom side of the fish.

This abstract from a 1978 paper describes an attempt to use 29 species of parasites (microsporidians (fungi), nematodes, trematodes, acanthocephalans (another worm type), leeches, and copepods, among others) in or on English Sole in Oregon.  The study attempted to correlate the fishes’ migrations with parasite infestation.

CONCLUSION:  English Sole have a lot of parasites!

4. Tapeworm.

Striped Bass caught on 16 June 2018.

A Unique San Francisco Bay Parasite wound in Striped Bass.  Click on this link:, then click on the menu item:  “Lesions in Striped Bass from San Francisco Bay.”  This explains red lesions we often see on striped bass – usually on the right side.  It’s a tapeworm! … Lacistorhynchus tenuis.

Neither the tapeworm nor Striped Bass are unique to SF Bay.  The same tapeworm infects the bass in other parts of the world as well.  But, according to the above link, only in SF Bay does the same tapeworm leave red lesions on our Striped Bass!

For years I had been blaming Lampreys for those red wounds.  My bad.

5. Lamprey.

Lampetra tridentata

Pacific Lamprey, or “Three-toothed Lamprey.”  We caught this jawless, boneless, ancient fish in Pond A21 using a 20mm larval net on January 19th.  The holes along the side are gill slits.  I read elsewhere that all lampreys have seven on each side. 

25 Lampreys have been caught in Hobbs’ trawls since 2011.  I am certain that normal Hobbs “Otter” trawls substantially undercount Lampreys because this eel-like fish can easily slip through the larger Otter mesh.  Holding it was an extreme challenge.  I don’t recall ever attempting to hold onto a fish with no bones.  As it slipped through my fingers and whipped itself into knots, the suckermouth was constantly bending back to plant itself on my hands or arms. 

Intellectually, I know that this little guy’s teeth are way too small to break my skin.  Even a full adult Lamprey is supposed to be fairly harmless to humans.  But, … EEEEEWWWWWW.  Just NO!  I couldn’t let him latch on to me.  And, that sucker mouth is strong.  I literally could not pull him off the plastic tray once he got a grip owing to his slipperiness and lack of bones.

Lamprey teeth against the magnifying glass.

In a panic over what to do with this writhing little monster, I remembered that Christina Parker ( had Facebook posted advice to always sucker-plant your lamprey on a magnifying glass.  That way you can easily examine his or her teeth.  So, that’s what I did.

I think we identify this as a Pacific Lamprey because the top three teeth of the inner ring look like fangs with a smaller tooth in between.  However, both Pacific Lamprey and River Lamprey inhabit these waters.  Identification between the two is tricky.  River Lamprey is described here:

This is a very long video from Oregon State University featuring two Lamprey experts.  The second presentation by Carl Schreck, starting at 15:14, is best.  If you have time, Carl’s presentation will teach you more about the life-cycle and importance of Lampreys than any book can: 

I learned from the Oregon video that our Lamprey shown above is likely a 5-to-6 year old “Smolt,” or “teenager” who has grown past the larval stage and is now heading out to sea. 

Did you know …

  • Pacific Lampreys can live 8 to 13 years? 
  • Millions and millions of their tiny larva pervade muddy and gravelly creek sediments? They are the earthworms of creek bottoms.
  • Practically all estuarine and riverine lifeforms evolved under the influence of Lampreys for roughly 360 million years?, AND
  • All of us advanced life forms, from fish, to reptiles, to birds and mammals are all descended from jawless fish somewhat like Lampreys?   

Lampreys are both traditional native food in the Pacific Northwest, in Baltic nations, and the food of royalty in England.  All sources agree that Lampreys have far higher fat and caloric content than just about any other river fish.  Like salmon, they deliver an enormous amount of protein up the rivers when they spawn and die.  They are delicious if you know how to cook them: 

This YouTube video shows a Lamprey restocking program that is being carried out in the Columbia River Basin.  Like many anadromous or catadromous fishes, dams and other barriers block them from their native streams. 

A USFWS video about Pacific Lamprey conservation, again in the Pacific Northwest:  (It makes me wonder, why are we not conserving Lampreys here?)

A recent story about success of a Lamprey ladder at the Cape Horn Dam in Mendocino County: 

Don’t eat the Lampreys! They are far too important in the local environment.  We need more lampreys!

… In summary, I read somewhere that there are at least three or four parasitic organisms for every potential host in the world.  I think it’s true!

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