15 DECEMBER 1999
Date: 28 Nov 1999
From: "bayview" <twister37@panax.com>
To: <AQUA-L@killick.ifmt.nf.ca>
I raise the giant sea scallop Placopecten magellanicus. I have 10
tanks. Each of my tanks are 12' x 19' x 6'(LxWxH) holding @ 35,000 liters of salt water (12-15 c). In each tank are 24 stacks of 36" x36" x 4" trays (each 4" x4" hole initially contains 1 12-15 mm spat) which are 4 across x 6 x 30 high. I change the water in each tank by pulse feeding with a 75 liter/min pump that pumps 1 hour ON/ 2 hours OFF 24 hours/day. By means of a venturi type system, I mix +/- 175 liters (equal mix) of 8 algae: CCMP 608, 910, 898, 1336, 1010, 429, 1315, 1012 (http://ccmp.bigelow.org). I grow the algae in 32(ct) 18" x60" clear k-walls(4/algae) in 24 hours light. I pass recirculated water through a filter / biofilter system< 1 micron. I use a 10 micron screen over-flow on the near top of each tank (going to the heated recirculation tank). Remember, a sea scallop only retains food 10-40 microns. I average @ 40 million cells/ml (counting method later in report).
GOAL: Total tank cell density of +/- 200,000 c/ml at each feeding. I refeed 2hrs later at @ 40,000 c/ml. Therfore I add 175 ltr. of equal mix algae 8x/24 hrs. This gives me a c/ml cell count of 200,000 c/ml at feeding time. PROBLEM: A scallop consumes 5% of its total body weight in dry algae weight/day. How much algae must I grow/day to feed a maximum of 500,000 +/- 80 mm scallops? (assuming a "meat count of 30-35/lb).
I fear I'm under-producing algae. So far I've lost 6,500 scallops with @ 75% losses occurring the first week (transfer shock, etc). This is my 4th week and my shell height is @ 25 mm (from 12 mm). My current tank water cell density is presently @25,000 c/ml at feeding time. Down from @ 120,000 initially. I get cell densities by "assuming" an initial density level and diluting a 1 ml sample accordingly in a 10, 20, etc liter vessel of distilled water and counting cells under a microscope (I also attempt to identify the # of each type of algae to record consumption/loss/non-contact/etc). This isn't the professional way to do this, but I have a 6-month $5,000.00 budget! My pH stays @ 7.2-7.4. I need to know about oxygen consumption, ammonia/nitrite/nitrate/ levels, etc, soon because my little critters are growing up fast and I don't want to kill them out of stupidity! I still need most importantly a feed formula to make sure I don't starve them. I have room to grow more algae..... Anything else I should watch for?
P.S.
I filter all in-coming sea water to 1 micron and totally clean each tank every other week.
Clark O'Shaughnessey
Ellsworth, Me, USA, (207)-667-8096
E-mail: twister37@panax.com
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COMMENTS 1 :
If you want to feed 5% dry meat weight of scallops in dry weight of algae you will need to get a mean scallop dry meat weight x scallop number and an estimate of the dry weight of your algae to establish your total feeding cell number.
See following for some dry weight data:
Brown, M. R. 1991: The amino-acid and sugar composition of 16 species of microalgae used in mariculture. Journal of Experimental Marine Biology and Ecology 145: 79-99.
Here is some details I have tabled:
micrograms/millon cells
C. calictrans 11.3
C. muelleri 74.8
Thalassiosira. p. 28.4
Dun. tert. 100
Nannochloris atomus 21.4
Nannochloris oculata 6.1
Tetraselmis chui 269
Tetraselmis suecica 168
Iso-t 29.7
Pav. luth. 102
After you have established the total cells you need to feed/day try to
break it up, so the cell density is not too high, otherwise the spat may waste feed by putting it to pseudofaeces.
Sam Buchanan
E-mail: buchanansam@hotmail.com
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COMMENTS 2 :
Thank you to all who responded to my first inquiry. I'm in my 5th week in my scallop project. I've only had 35 mortalities this week (out of 493,300 surviving!). I used the diet formulae suggested and doubled my food capacity (I won't get the additional volume for 2 more weeks or better, but at least I'm hopefully heading in the right direction).
I need to know if I need to start watching for ammonia/ nitrate/nitrite
levels. I don't have any more tanks to expand to... If I start getting mortalities soon, should I remove smaller scallops or should I increase oxygen, water flow, or what?
My pH is still a constant 7.2-7.4. I still recirculate my total water
volume in 24 hours.
My avg. shell height is now 29.75 mm. (still 0.6 mm/day).
Clark O'Shaughnessey
Ellsworth, Me, USA, (207)-667-8096
E-mail: twister37@panax.com
***************
COMMENTS 3 :
Keep in mind that the food demands of your scallops should increase
exponentially as the animals grow in size.
Also, you want to maintain cell densities in the range of 20-60,000
(depending on cell size) cells per ml (not 200,000!). See if you can
deliver the food at a slow, constant rate rather than all at once. I used a cheap commercial peristaltic pump or gravity drips.
At higher concentrations (5-25 mg/L) most bivalves tend to produce copious pseudofeces which are wasted cells. If in doubt, look at your feces under the scope and see if you have lots of intact cells.
Also, scallops prefer slightly larger cell sizes than other bivalves since
they lack the eulaterofrontal cirri. Therefore they have poor retention rates for particles smaller than 3 um. Stick with the larger diatoms and
dinoflagellates like Tetraselmis or Rhodomonas as opposed to T-iso or C. calcitrans.
I tried this with bay scallops about ten years ago, but they quickly ate
me out of house and home. As I recall, I had a few hundred animals about this size consuming about 200L of algae a day (3-5 million cells/ml) in three two-hour pulse feedings.
Robert B. Rheault
Moonstone Oysters
Narragansett RI
E-mail: oysters@ids.net