Learning About Fish

June 10th - 22nd (A Wednesday to a Monday)

Another twelve days of work has passed for us at the Mowi fish farm.  It was an exciting shift for us because every few days we were getting another load of fish.  The fish came up from one of the hatcheries near Campbell River and they arrived by boat in loads of about 510,000 fish.  Each of the large tanks at the farm holds 340,000 fish, so we would put 340,000 in one tank and the rest into another tank.  On the next load we would top up the last tank with 170,000, and then another 340,000 would go into the next tank.  Over the span of this shift we filled seven tanks, so we now have roughly 2,380,000 fish on site.  That is a lot of little mouths to feed.  

Because the fish arrived to us by boat they had to be pumped through large four-inch hoses to a small tank up on shore.  From there they were once again pumped through hoses to their main tank.  They had to get pumped into the first small tank from the boat because the distance was too great to pump them straight from the boat to the large tank.  

We also had to work around the tides since the lower the tide was, the lower the boat sat and the harder it had to pump to get the fish up into the small tank on land.  And, since we had to work around the tides, it meant that one of the days we could not start unloading the fish until around 16:00, so it ended up being a late night of work for us.  

The fish that we got are what are called parr.  They are older and bigger than fry and they are about an average weight of 20 grams.  They have very distinct parr marks on them, which help them to blend into a natural streambed.  From above they look very much like pebbles.  Atlantic Salmon have quite large ventral fins and when they swim with them out to the side they look like baby sharks from above.  

One thing that we learned that I found very interesting is that Salmon gulp air from the surface to regulate their buoyancy.  They then can burp this air when they are below.  Herring and some other baitfish also gulp air from above, but they fart it out instead of burping it to regulate their buoyancy.  In comparison, Rockfish have a way of taking oxygen from their bloodstream, which of course they get from their gills, to fill their swim bladders.  They cannot purge this air quickly like Salmon or Herring and instead it is a slow process in which they put the air back into their bloodstream to get rid of it.  This is why often when we pull a Rockfish up from the depths it has a very overinflated swim bladder and it cannot get back down to the bottom on its own.  

It has been quite interesting learning about raising fish; there sure is a lot to learn with everything from desired water composition and required dissolved oxygen levels, to best feeding practices, to feed and growth ratios.  It is quite neat that Salmon have the best food to growth ratio of any farmed animal.  It is 1.2, which means that if you feed a fish 1.2 kilograms of food it will grow 1 kilogram.  Quite impressive!  In comparison, beef, which has one of the worst feed conversion ratios, ranges between 6-10.  In other words you have to feed a cow between 6-10 kilograms of food in order for it to gain 1 kilogram of weight.  It will be very neat to come back for our next shift in two weeks (on July 7th) and see how much bigger the fish are.  

Now that we have fish on site, one of our daily tasks is to fill the automatic feed silos.  Even though the fish are still quite small, and only seven tanks are filled, we were still putting in one ton of food each day.  Like I said, it’s a lot of little mouths to feed.  The automatic feeding system feeds out about 90% of their daily food and the other 10% is hand fed.  This was a fun job as we got to go around to the tanks and throw feed to the fish.  It was definitely a skill to learn to be able to throw a scoop of food out in a nice even spread across the tank, but we got better and better at it with practice.