[Some of what follows appeared in a 11/15/16 blog I wrote. I've also broken this piece up with three nice pictures of students at Bellows Free Academy. Thanks, Melinda!]
Predicting and controlling when swim-up happens
At this fall's TIC workshop, we discussed two of the biggest challenges of raising brook trout:
when the fry swim up. A future post will talk about how to keep the breeder basket clean.
"Swim-up" is a stage that occurs when alevin become fully developed. Prior to that point, alevin have been living on the bottom of the breeder basket, but when they approach being 100% developed, they start making tentative movements towards the surface. Experienced fisheries biologists like Roxbury hatchery's Jeremy Whalen can recognize the fairly subtle cues that indicate the alevin have reached the swim-up stage (when they'll be called fry). But TIC teachers and volunteers, who observe only a comparatively small number of alevin and who raise trout just once a year, usually find it very difficult to spot the telltale signs of the swim-up stage. As a result, we need to use data to predict when fry will swim up.
And for this, we've created a data entry sheet and a special "swim-up calculator," which you can find here. (You can also find this spreadsheet in a folder called "Calculating Development Index," which is in the TIC Google Docs Collection, available from the TIC Resources page of this Web site.)
Thanks to the efforts of Lorena Schwarz and with some help from Castleton University statistics professor Abbess Rajia, this new file is much improved over the one we demonstrated at the workshop. A quick note about the Excel file attached to the link above: it contains four worksheets. The first provides instructions, the second is used to PREDICT swim-up and to record water temperature data, the third will allow you to DETERMINE or CONTROL when the alevin swim up, and the fourth you won't need to use, it simply allows a formula to perform a "lookup" function. Below I've included a screenshot of the four tabs that give you access to the three worksheets you'll need to use.
Predicting the swim-up stage
Development is a function of water temperature and time. With each day that hatchery or tank water is at a particular temperature, a constant is added to the previous day's cumulative Development Index (DI). This chart (below) shows the relationship between temperature (in tenths of a degree, which appear at the top of the columns) and the constant that is to be added to DI.
So, for example, at 49.3 degrees, the value of 1.146 is added to whatever the cumulative DI was on the previous day.
When schools got their eggs earlier this month, you should have entered the date you received your eggs into cell B4 in the "mm/dd" format, e.g., "01/06" would represent January 6 (image below). Either hatchery staff or your egg deliverer will be able to tell you how developed the eggs are on that day, that is, what their Cumulative DI is. This number is very important and should be entered into cell C5 of Sheet B.
From that point forward, all you needed to do is enter the daily water temperature into the cell in Column B that corresponds to the correct date. The spreadsheet will automatically calculate the new Cumulative DI.
It is important to enter water temperature data for every day, including weekends and school breaks, even if you haven't checked the tank temperature. For those days when you don't/didn't visit the tank, estimate (or "interpolate") the water temperature. So if the temperature was 51 when you left on Friday afternoon and it was 49 when you returned to the classroom on Monday morning, enter a temperature of 50 for each of the weekend days.
And don't let the bottom of the net breeder get too dirty! (More on this later.)
Controlling the swim-up stage
But what happens if you realize that swim-up is likely to occur when your school is scheduled to be on vacation or at a time when, perhaps because of a conference trip or personnel leave, you won't be able to diligently monitor your fish, looking for those subtle signs of the swim-up stage?
Here's an exchange between teacher Ted Nathanson (of East Montpelier Elementary School), volunteer Shawn Nailor, and Roxbury hatchery supervisor Jeremy Whalen:
TN to SN: Hope you had a nice weekend! Wanted to give you an update. On 1/11/17 we had 2 eggs that hatched. When I got in this morning we had 6 more over the weekend for a total of 8. Now at 3 o'clock, we have almost 30 total. They are going crazy!
The water temperature is at 52.2 and the water chemistry is all normal. Our pH is at 8, is that an ok level? Should we stay on track with the water temp of 52? Thanks!
SN to JW: Any suggestions or is this 'normal'?
JW to SN: At 52 degrees, this is normal. They must be pushing 58 DI at this point. If he stays at 52, though, the fish will start feeding before or during the next break. If his goal was to start feeding after February break, he needs to cool the tank off. (I later learned that Ted's DI was 53.67 on 1/16.)
SN to TN: I sent along your email to Jeremy and here's his reply (above).
TN to SN: Thanks for looking into that. Our last day before break is Feb 24th and we don't return until March 8. When I use the swim-up calculator and set the swim up for March 9th, I need to get the tank down to 46 degrees. Our break is longer than normal and starts later than most schools with presidents week off. Should we still shoot for swim up after break? Does this sound like a good plan?
So, sometimes you have to take control of your tank and its temperature to ensure that you're around and able to give lots of attention to your fish when they start to swim up.
That's when you need to use the third tab of the Excel file we discussed above (see image below).
When you click on that tab, it will take you to this "calculator" form.
As long as you've been maintaining the DI total (by keeping up the "Temp. entry and DI record" spreadsheet, as described above), you will be able to enter the three data elements called for in Cells B5, B6, and B7. Once you've entered the third of those ("Total DIs as of today"), you'll find out what temperature (it'll appear in B12) you need to set your tank at in order to have your fish swim up on the day you've chosen.
If the specified temperature is more than five degrees lower or higher than what it currently is, you might want to step your tank down (or up) more gradually. In that case, I'd recommend that, after your tank temperature has reached the target number, you redo the calculation (using the Swim-up calculator a second time) with the new numbers for DI and dates. This will permit you to fine-tune the temperature setting.
In a future post, I'll discuss breeder basket cleanliness as well as some tips for identifying when alevin are approaching the swim-up moment.
Joe Mark, Lead Facilitator, Vermont Trout in the Classroom
In June 2012, I retired after 40 years in higher education, having spent the last 32 years of my career as dean at Castleton. One of the first things I volunteered to do in retirement was to work with Jim Mirenda to help the Dorset School, where his kids and my Vermont grandkids attend, start a TIC program. Gradually that commitment grew into my current role, which is both demanding and highly rewarding.