October 2004 - Mercury?

Hey Chuck...I will attempt to answer your question, but don't be offended if I insult your intelligence. I just want to make it as understandable as possible and I'm sure much of it is common knowledge to many fishermen and conservationists.
Mercury accumulation in fish occurs through what is called biomagnification. The process goes like this: 1) Mercury enters the system through the burning of fossils fuels, specifically coal, and proceeds into the atmosphere. 2) The mercury in the atmosphere is re-introduced into the system either through rain or simple deposition. 3) The mercury enters the aquatic system and is held in the water and soils. 4) This is where the biomagnification occurs.
Biomagnification is the process by which mercury concentrations magnify as you go up the food chain. Plankton and macroinvertebrates are the first level of mercury consumers. They are subsequently eaten by your minnows, juvenile predators, other inverts, etc. These are then eaten by the larger predators and so on.... The level of mercury concentration rises with each level of the food chain.
Now you ask why would a bowfin be that much higher than a largemouth? Consider how much food a bowfin eats compared to a largemouth. Comparable, right? Now consider the maximum age of each species, this is where the difference comes about. Bowfin are longer lived fish than largemouth, pickerel, etc. Thus the amount of food a bowfin eats in its lifetime will be considerably higher than that of other predators.
To answer your other question about mercury metabolism, fish do not have effective methods of metabolizing mercury; once it is in the fish it is basically there for good. So overall it is relatively easy to make an estimate on the mercury concentration you will find in fish within the same system. Fish that eat fish will be higher in general, and the oldest of these fish eating fish will be the highest. NOT ALWAYS TRUE, BUT IT IS PRETTY CLOSE!!
Dusty E

September 2004 - Historical Range and Stocking

Yes, bowfin fossils exist out west. At one time much of the west was under water. This expedition at Bryce Canyon in Utah reports Amia at several levels in the strata. Several Eastern states have stocked bowfin, but this was many years ago. The only current stocking ideas are for aquaculture, since bowfin roe is sold as a "poor man's" caviar. Self-stocking is discouraged, and there is no current interest is stocking bowfin as a sportfish. Washington State explictly bans the stocking of Bowfin, but I was unable find a similar statement in the CA 2006 Freshwater Fishing Regs. It may there, I just couldn't find it.

February 2004

If you or any of the BAG members want to do your own database searches, you can logon to the National Library of Medicine website (http://www.ncbi.nlm.nih.gov/) and get a list of articles (some will have links to the actual articles) on whatever topic you wish. Go to the site and click on the 'PubMed' tab. Type in any keywords in the the 'for' box (e.g. Amia calva), hit 'GO' and see what comes up. I got 78 hits for Amia calva. This is not a comprehensive site since it will only find journals that submit results to the National Library of Medicine, but it's not bad.

You can also try the FishBase website (http://www.fishbase.org/), but I think I saw that listed somewhere on the GASSBAG website.

The periodicity paper was based on videotaped observations of 8 hr sessions (overnight) with individual bowfin in aquaria. I saw lots of interesting behaviors, including 'yawning' and the ability of bowfin to 'abort' air-breathing attempts. They certainly can sit on the bottom and not surface breathe if there is a threat at the surface. This is well-known from observations of other air-breathing fish, too. They appear to rely more heavily on gill ventilation during times when they are avoiding air-breathing.
Air-breathing will also depend to a large extent upon water temperature - the higher the temperature, the higher the metabolism and the greater reliance on air-breathing to support that metabolism and buoyancy. I don't have any data on whether feeding or satiety influences air-breathing behavior. My gut feeling is that it probably doesn't influence it very much - but if it does, then I might expect them to breathe more after feeding since feeding will raise metabolism. But I am just speculating here. There may be some data on feeding/air-breathing in other species and I will see if I can find it.
Bottom line is that air-breathing is a complex behavior that can't be classified as an involuntary reflex; although 'simple' signals like decreases in oxygen and lung volume may trigger the air-breath, higher centers in the brain can override these signals under certain conditions (e.g. the threat of a BAG member).

The distinction, and purpose, between Type I breaths and Type II breaths was a major part of my research on bowfin. Type I breaths had been described, but Type II breaths had not. It is clear to me that Type II breaths (inhale only) serve a buoyancy function while Type I breaths (exhale-inhale) are used to gain oxygen. This makes 'sense' because fins (and gar) must use the same organ (gas bladder) for both purposes. The two functions (gas exchange and buoyancy) have different requirements: a good 'lung' needs to have oxygen leave quickly (and loses volume) while a good 'buoyancy organ' needs to retain the gas, but is a lousy gas exchanger. I think that fins (and perhaps other air-breathers) have 'invented' the two breaths to take care of these different roles of the gas bladder. Type I breaths do take slightly longer (about 0.5 sec) than Type II breaths (0.1-0.2 sec), but you may not notice this at the surface. If you took a fin home and put in in an aquarium, you could easily distinguish the two breaths. Sometimes bubbles are lost through the opercular (gill) cavity after inhalation during descent. Again, you probably wouldn't notice them unless it happened right next to you. Exhalation occurs through the mouth in fins, which is different from gar which exhale through the operculum just before breaking the surface.

There is a large spectrum of fish gill 'efficiencies'; bowfin are not the worst or the best. My friend, Steve Katz, and I created a computer-generated model about this and found that air-breathing could enhance the efficiency of the gill, but whether this happens in 'real life' we can't say with certainty. Another hypothesis (Colleen Farmer) is that air-breathing improves cardiac oxygen levels and is there to improve cardiac function. In other words, like an external coronary circulation. My own view is that air-breathing evolved to regulate buoyancy first, and then became important in low oxygen situations.

Air-breathing can reduce the recovery time after strenuous activity, which has been shown in both bowfin and gar. But bowfin are generally not too active in general (i.e. not continusly swimming), but are more 'sit and wait' predators that will strike at prey (or your favorite lure). But if they are active, chances are they will air-breathe more to help in the recovery process.

Both questions are related, so I'll give one answer: The question of 'why' something evolved is almost impossible to answer. But, again, my own view is that buoyancy was the dominant reason for air-breathing, and hypoxia occurred secondarily. The reason I think this way is starting from basic physics: any gas taken into the body of an aquatic animal automatically changes the buoyancy of the animal, regardless of whether that gas (oxygen) is used by the tissues. The earliest fish were very heavy-bodied, bottom feeders; having a way to exploit a bigger niche by air-breathing and adjusting buoyancy is a nice way to increase survival. Most of the modern air-breathers evolved in hypoxic habitats and became air-breathers secondarily.

Bowfin are the sister-group to all modern teleosts. That is, all teleosts are more closely related to bowfin than other fishes. Gar are older than bowfin. All of these fish are ray-finned fishes which split from the other group (lobe-finned fishes) several hundred million years ago. True lungfish are lobe-finned fishes and are the only air-breathers that lead to the lineage of all terrestrial animals, including us. Therefore, bowfin are just part of a continuum of fishes that split from the group that was evolving toward terrestriality.

The design apparently does work well. Teleosts probably displaced all of the bowfin (except Amia calva) because of the 'invention' of a true gas bladder and the ability to exploit more niches. It's not clear how common air-breathing was - it could have been pretty commmon. Modern air-breathing teleosts have used a number of structures to hold air, especially in hypoxic environments (e.g., mouth, gut, etc) while using the gas bladder for buoyancy.

A large bony plate in the ventral part of the mouth, the gular plate probably serves to protect the animal. It moves a lot during an air breath. Other fishes do have a gular plate.

It wouldn't surprise me to find that the barbels serve some tactile function for finding prey; I don't know of any studies that have looked at them for a possible chemoreceptive function. There are lots of data on catfish (John Caprio at Louisana State Univ. has done a lot of work with this) but none that I know of with bowfin. In the grand scheme, very few of us care at all about bowfin. That is shocking, I know, but true. I really appreciate the efforts of the BAG members in raising the awareness of the bowfin! Great job!

Being on the west coast, where there are no bowfin, I am not in touch with any potential projects. You could contact your local F&G guys and ask them if they know about any projects.

The gas bladder is vascularized, but is a very simple structure. It doesn't have any real elaborations like alveoli. The capillaries drain into a venous sinus that empties into the venous supply just outside the heart.