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collection of bluegill from spring


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#1 Guest_centrarchid_*

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Posted 11 April 2007 - 06:36 AM

I have been attempting to acquire 6 to 9 inch bluegill (Coppernose / Southeastern / Florida subspecies) from a Otter spring (privately owned) off the Suwannee River, FL for use in a genetics / breeding study. Success has been low owing to complications that manifest even before fish removed from water. I suspect the bends. Observations of free ranging bluegill indicate they ventilate / breath heavy without being stressed. The Suwannee River drainage has to date not offered an easier collection site.

Fish captured at depth ranging from 12 to 25 feet using either angling / 12 foot deep x 100 foot long seine / dipnet. Angling resulted in the greatest losses. Seine requires driving fish into shallow water where they clearly to not want to go and stresses non-targets (also too much work). Dipnet works best after dark. Fish brought to near surface will immediately float the rest of the way up unless they actively power swim back down. Fish darken and eyes cloud. Ventilation rate picks way up and on about half of the fish necrosis of all fins begins within hours. I use water from spring, and initially transferred the fish to a fish hauler, increased salinity (NaCl) to 2 ppt and added oxygen using compressed O2 and a fine pore diffuser. A co-worker suggested increasing oxygen concentrating may slow gas balancing by slowing ventialtion rate so I stopped supplementing. No change. Contacts at the Tennessee and Shed Aquariums suggested use of a decompression chamber which then employed and started at a depth of twelve feet. The chamber was moved into shallower water at 2 foot increments every hour. Over all survival improved but some animals were clearly very stressed (extrememly high ventilation rate and fin necrosis) in the chamber and ultimately required the most intensive hospitalization. Animals that were easiest to catch had the greatest problems but generally all were easily caught even as a I used a dipnet while free diving (snorkeling) without flippers. Fish taken to the lab frequently had eye problems. I resorted to treating fish agressively with antibiotics to control necrosis. Oxytetracline was ineffective therefore Marycin-2 or Furacin were used. Use of the latter two increases the time required to get animals into breeding condition and thus a better option is desired.

Any ideas on this mess?

#2 Guest_fundulus_*

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Posted 11 April 2007 - 07:14 AM

Is the spring water supersaturated with O2 or some other gas at depth? Otherwise the only solution I could offer would be extremely slow removal of the fish. Bluegills in my experience aren't typically found at the depth you're collecting them, these are almost extremophile bluegills.

#3 Guest_centrarchid_*

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Posted 11 April 2007 - 08:03 AM

Oxygen concentrations were definantly low (4 mg/L) although in themselves not low enough in my opinion to cause such a problem. We suspect the water welling up is superated with molecular nitrogen (N2). In the mainstem of the Suwannee the bluegill have access to such depths and in the midwest with the northern bluegill with which I am more familiar that can be found at depths exceeding 35 feet so long as oxygen concentrations are high enough and even greater if food is also present. Thermocline seems to be a partial barrier but this not an issue in the spring of concern. This fall we may increase the intervals between moving decompression chamber but as I indicated previously signs of stress were apparent even then and often when the chamber was at the maximum depth of 12 feet.

#4 Guest_gerald_*

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Posted 11 April 2007 - 10:33 AM

Try bringing a tank of non-spring water (salted) that you know is fish-safe with you and put the fish directly in this after capture. sounds like something in that spring water itself jest aint right; the fish tolerate it OK until theyre stressed by capture. maybe something stirred up from the sed during collecting ?? when i collect in extreme acid habitats i often bring along salted water for dilution for this reason. also try a DARK color container to reduce the fright response, with a "roof" of floating plants to ease their tender fishy nerves. that fin necrosis sounds like rapid ion loss associated with fright. you might also consider using a mild sedative ?

Is the spring water supersaturated with O2 or some other gas at depth? Otherwise the only solution I could offer would be extremely slow removal of the fish. Bluegills in my experience aren't typically found at the depth you're collecting them, these are almost extremophile bluegills.



#5 Guest_bullhead_*

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Posted 11 April 2007 - 11:48 AM

Yes, gerald has a good idea. It almost sounds like the upper water layer contains some toxin or chemical difference, probably not just temperature or salinity. Further evidence of this is that the fish started showing distress while still in relatively deep water in the decompression chamber (am I reading your remarks correctly?). Is there flora/fauna in the upper layer?

#6 Guest_centrarchid_*

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Posted 11 April 2007 - 04:37 PM

Yes, gerald has a good idea. It almost sounds like the upper water layer contains some toxin or chemical difference, probably not just temperature or salinity. Further evidence of this is that the fish started showing distress while still in relatively deep water in the decompression chamber (am I reading your remarks correctly?). Is there flora/fauna in the upper layer?



Otter spring is a spring with volume of pool being turned over in less than 30 minutes. Yes, for remarks correctly. Water not stratified owing to spring flow and only fauna / flora layering evident associated with aufwuchs that varies as a function of sunlight and grazing activity. Will make the decompression chamber black or gray and add a mineral / salt block next run.

Thanks

#7 Guest_smbass_*

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Posted 12 April 2007 - 12:10 AM

Is there a reason why you are targeting fish from this exact location or do you just want fish from the Suwanee river drainage? I ask because I was there last May and had a great time catching Florida bluegill, spotted sunfish, redear sunfish , redbreast sunfish, and warmouth from some pools in a spring run that had been cut off due to low water. These fish were very abundant and easy to catch on a fly rod off the surface which would say you all the trouble from getting them down so deep. Anyways this was at the Suwanee River state park so it was public access.

#8 Guest_centrarchid_*

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Posted 12 April 2007 - 05:40 AM

Is there a reason why you are targeting fish from this exact location or do you just want fish from the Suwanee river drainage? I ask because I was there last May and had a great time catching Florida bluegill, spotted sunfish, redear sunfish , redbreast sunfish, and warmouth from some pools in a spring run that had been cut off due to low water. These fish were very abundant and easy to catch on a fly rod off the surface which would say you all the trouble from getting them down so deep. Anyways this was at the Suwanee River state park so it was public access.


I needed native fishes from the Suwanee river drainage and a reliable place to get them since I iniitially intended to acquire them from 2 other locations in the state with six hour drives between. I obtained all I need for now but by this fall I wil need to acquire another 20 animals and if conditions allow I will try what you suggest.

The Florida biologists indicated that bluegill were not particularly abundant anywhere in the Suwannee River drainage, relative to the other species you mention, and by the time I went down for the first time in January the river was coming back up because the drought was easing. Also during the times I sampled (January and Febuary) mainstem water temperatures where not conducive to angling for bluegill. Another point was the photo opportunity as the spring I collected from was far the best (based on number of fishes, size) relative to the at least ten publically owned springs I checked. The latter appeared angled to death and the bluegill that were present looked like crap.

#9 Guest_Mysteryman_*

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Posted 06 May 2007 - 09:09 AM

Dumb question time: Why is 12 feet the maximum depth of your decompression cage? As any SCUBA diver can attest, the zone between 10 and 33 feet is where the most risk lies, so if you haul them up from 30 straight to 12, you've already done most of the damage you can do. If you set up your decomp cage at 25 feet and only bring it up two feet per 4 hours, you should probably not have any of these problems. Yes, that is extreme overkill, but you seem to be in an oddly extreme situation.

#10 Guest_centrarchid_*

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Posted 06 May 2007 - 10:05 AM

The cage could be set deeper but difficult owing to vertical cave walls. Gases super-saturated all the way to surface just as discharged from spring opening. Most fish actually captured 10 to 15 feet down. This is not the classical bends problem where only a change in depth of fish is issue. It is water they are immersed in as well. Problems become evident even before fish begin staging up for decompression. Super-saturated nature of spring water may also be transient and related to drought.


I have at this point gotten a few animals back and will breed them to generate needed experimental animals for next year. I have no intention of wasting time on fishes from such a situation again! I think now that at least some of those Florida springs are population sinks for fishes that occupy them. I have never seen so many sick fish even without my disruptions. Otherwise the springs are quite scenic. The little fishes seemed to do alright.

#11 Guest_Irate Mormon_*

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Posted 06 May 2007 - 06:18 PM

It's possible that they are stressed by the light (higher intensity close to the surface). I've seen dramatic reactions to stong light in fishes which were not used to it.



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