Hi everyone,

I have been holding 30 Alaska blackfish (mixed ages and sexes) in an 80-gal long fiberglass tank for 6 weeks in our lab on campus. I'm studying their diet and life history and am trying to rear adults for either spawning or stripping gametes for artificial fertilization. The fish have been under 12L/12D photoperiod and a temperature of 16 degrees C. All fish are fed frozen bloodworms.

In the past 2 weeks, 2 large males have become very aggressive and territorial, jaw-locking with each other and attacking other fish. I just set up a second 80-gal tank to separate the smaller fish from these 2 territorial males. Based on your experience with mudminnows, what would you suggest I do to try to either spawn these fish or bring them into fully mature/ripe condition? I'm limited to just the 2 tanks, and I'm becoming fairly good at sexing these fish. Some are 1-2 year olds, too young to spawn.

I videotaped a male cannibalizing other blackfish and hope to post that soon on You Tube!

Thanks for your help!

Dona

Here's the video of a male blackfish cannibalizing another blackfish:



(Strongly suggest watching with the volume muted )

I had to leave and when I came back 3 hours later (see end of video sequence), the prey was gone. Can't believe he consumed the other fish that fast!

You read descriptions of these fish being sluggish bottom-dwellers, but they can hold in a water column very well (dissections reveal a very large and well-developed swim bladder), and a classic pose is a 45 degree angle tilted toward the surface watching for prey.

Dona,

Have tried a partition yet? It appears your big males are using tank mates as conditioning food. Can you get your fish to eat something other than frozen blood worms? They are high in protein but low in other nutrients and a low quality conditioning food for most fish species I have fed blood worms to. Do you have access to lumpfish or other fish species eggs? They could be mixed in with blood worms to diversify diet.

Background of tank very bright. My fish on such a background in direct light tend to be stressed.

partition is nearly ready to install (had a bit of a set-back when the sheet of plexiglass I bought kept splitting when I drilled holes in it....)

hmmm, need to think of a different food as per your advice. No lumpfish eggs available. Plenty of frozen adult artemia in the lab, but it makes such a mess I don't like using it. Is it good and nutritious?

Have found several dissected blackfish with livers showing a mysterious dark spot. Could the diet of bloodworms be causing this, do you think? I've emailed our State fish pathology lab for advice too.

I'll see about changing the white bright background. Thanks!

We use a whole saw to make holes in plexiglass because of the splitting issue with larger drill bits.

For conditioning, I strongly recommend some sort of fat laden fish product. Can you acquire chunks of salmon that are harvested before salmon makes spawning run? Can you get your blackfish to consume from your hand or from the tip of a stick? You blackfish are in many respects similar to my warmouth. I think conditioning efforts will benefit greatly if you can get your fish to "feed up" regularly with nutrient dense feeds.

I am not familiar enough with blackfish to advise in respect to normal liver appearance, but a smaller than average liver is to be expected in nutrient intake too low. With the fishes I have worked with, it is hard to get growth from bloodworm diet that compares favorably with more nutrient dense feeds.


The tank in which you filmed the cannibalism; will that be the breeding tank?

Also, are the females to be used small enough for the male to consume? If so, then you may need to control interactions between males and females more than a partition will allow.

Have you seen any behavior of males you suspect to be courtship?

I've not observed any courtship behavior by these 2 males. Other smaller males are also aggressive, though I am assuming they are too small to breed based on other literature I've read. Saw the 2 "bulls" engage in jaw-locking combat while a smaller male(?) zoomed in and latched onto the operculum of one. I thought it had taken a bite out of the bigger fish. Separated them by scooping them up in a net (they still wouldn't let go until I gently pulled them apart.)

I'm sure I could hand feed them, as they bite my hand, even jumping out of the water to do so. They attack siphon hoses, etc. I'm assuming only the males which have been held at warmer temps and increased photoperiod are the aggressive ones, as other smaller fish (assuming females) spend time hiding or sitting on the bottom.

I think I could locate some (freezer-burned) salmon in friends' freezers to use for supplemental food.

Mature females are smaller than males, but not small enough to become prey, I'm pretty sure.

Yes, the tank where the video was filmed is the spawning tank, with a second identical tank nearby. They both are on the floor beneath stacks of small glass aquaria housing stickleback (for perchlorate toxicology work; a student in our lab discovered that perchlorate causes hermaphroditism in threespine stickleback....) I have only a 24 inch flourescent light on each tank, positioned in the middle. I don't have a way of altering water temp (we don't at present own a chiller.)

In April, I will be setting up 4-5 200 gallon white plastic tanks outdoors for holding blackfish for additional spawning investigations. All fish I have used so far were collected in a blackfish-only pond, a shallow man-made pond which has abundant blackfish (although I've trapped barely 2-3 per month since December; we are speculating they are buried in sediment at present, based on what folks in rural Alaska tell us.)

Should I try to darken these white fiberglass tanks by painting the interiors a dark color?

Dona

I have spawned central mudminnows here in Michigan. I winter northern fishes in a room where the water today in about 5 C and the light is on 10 hours. We get down to 9 hours per day in Dec. Most northern fishes I work with start to spawn at 16 C the mudminnows spawned at 10 C. I am not looking for eggs at that temp and only noticed the spawn when I saw fungused eggs. I only saved one egg which I did raise to adult size. Interesting they have a notochord. I feed the mudminnows frozen brine shrimp. At present I am trying again with 2 males and four females in one tank and 2 and 2 in another. The water today is at 5 C and the light level is at about 10 hours. The room raises in temp naturally and I add 15 minutes of light each week. I would expect if I get a spawn it will be in late March. All the northern fishes I have worked with seem to use the increasing light and temp to signal spawning season. I don't know you’re out side temps and Alaska’s light conditions, but I would think 16 C is to warm.

Good Luck
Bob Muller

Reads like your males are like Siamese fighting fish or roosters. Can you take a smaller aggressive male and attempt to manually express semen from him? You may find sexual competitence that is not expressed by smaller males when larger males are present.

It appears male blackfish may normally have discrete territories during the breeding season. If so, then you will have to accommodate them or restrict male movement as we discussed before with partitions. Also, I had a similar problem with male bettas I bred without confininng females except when observed. The trick was to put a wall or mass of vegetation the female can hide in away from the core of the males territory. The male clearly tracked the females by scent through vegetation but the effort required appeared to keep the male from investing much effort in the pursuit. The females could then effectively control when interactions occured.


Try the hand feeding but do not use freezer burned salmon. The freezer burn / rancidity is caused by degredation of the very same fatty acids you want to get into your fish, expecially the female blackfish.

If the females are the target of the agression and they have no way to get away from areas where males will interact with them on a regular basis, then the females may be stressed enough to prevent normal ripening of gametes and mating behavior. Most of the fishes I have bred where the male is aggresive during courtship, the female is also in an aggressive phase as she approaches the male. If her social rank is constantly suppressed by aggressive males, then she may not be able make switch into breeding mode.


You can diffuse the light either by having rays bounce off ceiling before going into the tank (turn light source upside down) or have light shine through some sort of thin cloth or paper. To complicate things, you fish might prefer more intense light with shaded areas to hide in. My nesting fliers had that aggrevating habit.


Yes, darken white fiberglass tanks. We multiple-purpose our tanks so to limit cost associated with painting in some situations, we use gravel or sand on bottom. It reversibly covers the bottom, can help with bio-filtration and as an added bonus facilitates fixing of semi-bouyant structure such as plants. Might enable detection of substrate moving behaviors. You might consider silt or organic materials if similar to natural ponds supporting blackfish.

Dona

I have spawned central mudminnows here in Michigan. I winter northern fishes in a room where the water today in about 5 C and the light is on 10 hours. We get down to 9 hours per day in Dec. Most northern fishes I work with start to spawn at 16 C the mudminnows spawned at 10 C. I am not looking for eggs at that temp and only noticed the spawn when I saw fungused eggs. I only saved one egg which I did raise to adult size. Interesting they have a notochord. I feed the mudminnows frozen brine shrimp. At present I am trying again with 2 males and four females in one tank and 2 and 2 in another. The water today is at 5 C and the light level is at about 10 hours. The room raises in temp naturally and I add 15 minutes of light each week. I would expect if I get a spawn it will be in late March. All the northern fishes I have worked with seem to use the increasing light and temp to signal spawning season. I don't know you’re out side temps and Alaska’s light conditions, but I would think 16 C is to warm.

Good Luck
Bob Muller

Thank you, Bob. I look forward to hearing about your upcoming successful spawn and greatly appreciate the info! It does indeed sound like keeping the blackfish at 16 degrees C is much too warm. They are all in darkness under 30 inches of ice at present, in their natural pond.

Reads like your males are like Siamese fighting fish or roosters. Can you take a smaller aggressive male and attempt to manually express semen from him? You may find sexual competitence that is not expressed by smaller males when larger males are present.

It appears male blackfish may normally have discrete territories during the breeding season. If so, then you will have to accommodate them or restrict male movement as we discussed before with partitions. Also, I had a similar problem with male bettas I bred without confininng females except when observed. The trick was to put a wall or mass of vegetation the female can hide in away from the core of the males territory. The male clearly tracked the females by scent through vegetation but the effort required appeared to keep the male from investing much effort in the pursuit. The females could then effectively control when interactions occured.


Try the hand feeding but do not use freezer burned salmon. The freezer burn / rancidity is caused by degredation of the very same fatty acids you want to get into your fish, expecially the female blackfish.

If the females are the target of the agression and they have no way to get away from areas where males will interact with them on a regular basis, then the females may be stressed enough to prevent normal ripening of gametes and mating behavior. Most of the fishes I have bred where the male is aggresive during courtship, the female is also in an aggressive phase as she approaches the male. If her social rank is constantly suppressed by aggressive males, then she may not be able make switch into breeding mode.


You can diffuse the light either by having rays bounce off ceiling before going into the tank (turn light source upside down) or have light shine through some sort of thin cloth or paper. To complicate things, you fish might prefer more intense light with shaded areas to hide in. My nesting fliers had that aggrevating habit.


Yes, darken white fiberglass tanks. We multiple-purpose our tanks so to limit cost associated with painting in some situations, we use gravel or sand on bottom. It reversibly covers the bottom, can help with bio-filtration and as an added bonus facilitates fixing of semi-bouyant structure such as plants. Might enable detection of substrate moving behaviors. You might consider silt or organic materials if similar to natural ponds supporting blackfish.

So appreciate all the advice! I'll add dark sand to the bottom of the fiberglass tank for starters. I have a few smaller males I could sacrifice, to check for milt. Last summer when I unsuccessfully tried holding blackfish, collected the first week of May, in outdoor pools, to bring them into reproductive condition, their eggs developed but never quite fully ripened. Clearly some key factor was missing. All were fed with bloodworms (alive and frozen.) Plastic wading pools were too shallow and temperature fluctuations were a problem.

I agree, 16 degrees is too warm. As for darkness, 30" of ice should allow enough light to see and some photosynthesis unless snow cover also a factor. What kind of winter temperatures are experienced from southern part of blackfish range?

Yes, you will have to moderate temperature fluctuations in outdoor tanks. Larger water volumes, partial placement below ground level can help. Do you have a larger pond close by that you can pump water from into your tanks on a more or less continous basis? Would moderate temperature if pump depth can be managed.

[...]
Good Luck
Bob Muller

Bob, it's awesome to see you posting here. Hope we'll see more of you.
(Sorry to wander briefly off topic, but post #1 from Bob Muller is quite an event).

Bob,

Did you see levels of aggression in your mudminnows similar to Dona's blackfish around the time you thought spawning was taking place?



Dona,

The thermal regimen your fish have been through indoors maybe way too high, especially for females. This could easily be the case even with the proper photoperiod regimen. Your males may still be a good sperm source to use with manual fertilization. What is the typical water temperature around the time blackfish are thought to spawn?

I am totally ignorant about blackfish. Well, Alaskan blackfish anyway. I know a bit about Tautog [a large marine temporate wrasse].

my mudminnow breeding

I don't know if you saw this further back in this forum, but here is my account of breeding central mudminnows which had been kept in a bucket of ice fishing bait left outdoors. I used night crawlers to fatten the female and color the male. Worked really well and really fast. From the frozen bait bucket, the fish went to approximately 50 F in my cellar. My lighting was on a timer at 14 hours day light, almost zero influence from outside light in my cellar.

I noticed I refer to baby brine shrimp as BBS which is confusing because lately I've been using BBS for blackbanded sunfish. I know, that's why I shouldn't use common names.

Edited by mikez, 19 February 2010 - 08:19 PM.

Thanks, Mike, for your amazing post with photos of your successful mudminnow breeding. So, one can differentiate between bbs and BBS, hah! Reading your description of the fish in a partially frozen bucket of water sounds like stories of rural folks here keeping blackfish outdoors during winter, to "thaw" and boil live to eat. It would be great to fly to one of the smaller W AK communities to get first-hand accounts of overwintering blackfish. (Have never tried eating them myself.)

Bob and Jim, the pond temp right now is about 4 degrees C with variable snow cover and bad-smelling dark-colored water. Our daylight today is 9 1/2 hrs.

These fish were all trapped on Dec. 27; 12 traps in 4 holes for 3 hrs. yielded 75+ fish, more than needed for my diet study, so I placed some in our lab tank for observation. Since then, monthly trappings have yielded almost no fish. I'm wondering if they burrowed into mud for the rest of the winter? Native Alaskans describe harvesting them in winter by digging them out of mud. In an stream near this pond, blackfish trappings are also sparse, although juvenile coho are present.

The males are still aggressive; yesterday during cleaning and feeding, one kept attacking my hand and the siphon plus the operculum of another large male.

Edited by FishofSchool, 20 February 2010 - 11:29 AM.

Again, bearing in mind I haven't yet even read a wiki on blackfish....
As a life long ice fisherman and based on my observation of those central mudminnows, pretty much no fish burrows into mud for the winter. The mudminnows in the frozen bucket were alert and active and hungry.

I'd bet your recent lack of success trapping can be found in the phrase "bad-smelling dark-colored water". Great description of the beginning of winterkill. I'd bet your fish aren't buried under mud, I'd bet they're hovering just below the ice trying get oxygen. Or maybe they do settle to the bottom in a torpid state. If so, it's the reduced oxygen and building nitrates, not winter that's shutting them down.

Ever have fish come up and start gasping at the surface of a hole in the ice? Classic winterkill. Blackfish may be more tolerant and you might not see them doing it but they're still under stress.

Here's a good website for general info on blackfish:

http://www.adfg.stat...sh/blackfsh.php

This site (scroll down midway to "Blackfish are surfacing" on 2/5/08) shows neat photos of blackfish traps:

http://www.deltadisc...robertnick.html

It does indeed sound like fish in this small shallow pond must be severely stressed from winterkill conditions. I only started trapping here last summer, and I'll be interested to see if the abundant, thriving population is still there come spring break-up. A duck hunting club uses this pond to train their hunting dogs, and they were very surprised to hear there were any fish in it. I expected to see stressed fish gathering at my freshly-drilled ice holes 2 weeks ago, but did not.

A retired professor at University of Alaska Fairbanks who wrote a much-cited chapter on fish overwintering in Alaska and is quite an awesome fish expert, told me about rural folks digging blackfish out of mud during winter; fish appeared to be encased in mucous cocoons, at least in some cases. It's hard to imagine how a fish, by very nature of its physiology and structure, could survive buried in mud. By studying these fish, we are trying to sort out fact from fiction.

The stories out there of blackfish survival feats read like a freshwater version of a Jules Verne sci-fi.

The becoming encased with mud does not make sense unless the gas exchange organ can be charged with air. Do blackfish appear to stand above the water line under the nice? Fish occuring in midwest ponds can become stranded if pond level drops but they typically dessicate, freeze solid or die of suffication. Air, possibly breathable, is often present around pond perimeter.

Have not yet seen them gathering at any ice holes I've drilled so far at 3 different locations (pond, stream, and urban lake) so I can't say. Several guys at the lake have told me where to trap in winter, to get them gathering in "swarms" at open holes. I think someone said to try trapping at dusk. I'm no ice fisherman...what do you think?