Category Archives: Trout life cycle

Alevins, North Walls, Trout life cycle

North Walls School alevins released in the Ore Burn

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I’m delighted to publish this report which Cameron Stout, the Class 2 teacher at North Walls emailed me. It was written by his pupils for the April issue of The Blether, “the newsletter of the community of Hoy and Walls” and when reading it, we can tell how much enthusiasm and commitment went into the project:

Brown trout fry, ready to be released by Levi in the Ore Burn

Away back at the beginning of Term 3 (January), Class 2 got some trout eggs from Jim Erskine so that we could take part in the Troot in the Shed project. Everyone was very excited about it since some of us did a similar project a few years ago and we were really looking forward to taking part in it again.

First of all we had to prepare a tank in the shed – the shed is best because it is at a cooler temperature. If the eggs and baby fish (alevins and fry) get too warm it can kill them.

We put the eggs in the tank carefully. We had to watch in case the eggs went white. That meant they had died. We were fortunate though, because not many of them died. Out of our total of 300, only about 40 didn’t survive. We think it’s possibly because they had to make an extra journey across to North Walls on the boat.

We had to check on the eggs frequently, recording the air temperature and water temperature, and whether any had died. If they had, we had to remove them from the tank within 24 hours.

As they grew, we noticed that their yolk sacs started to shrink. The yolk sac contains the food that they use when they are first hatched. At this stage, they are approximately 1.5cm in length.

They were very small and their eyes looked gigantic. They wriggled in the corners of the tank – probably trying to hide among the stones.

There is a microscope in the science room so we used that to examine them closely. It was fascinating to see them so close up.

When they got older, their colour turned darker and we noticed that their yolk sacs had almost disappeared. At that stage they start being called fry and they come up to the surface to look for food.

Almost at the end of the project we took a walk to the Ore Burn to release them. Everyone had a shot of scooping out a net with between 5 and 20 in it, and transferring them to a bag of burn water that we had at the ready. The reason we do that is so that there is not too big a change of temperature, and so that they do not fall in from too high a height.

We took great care handling the troot as they were very small.

Now that they are in the burn, the survivors will probably stay under the brig until they’re a bit bigger and then they will head to the sea.

We learnt about life cycles and we can now compare the trout life cycle to the human life cycle and other parts of nature.

We would like to say thank you to Mr Erskine and the Orkney Trout Fishing Association for preparing the whole project and involving us in it. We hope to do it again.

Craig scooping the alevins before release in the Ore Burn

Alevins, Stronsay, Trout life cycle

Stronsay pupils release their fry into the Meikle Water

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Spring was in the air on March 28th when the time had come to release the alevins hatched at the Stronsay School. The island was bathed in sunshine and the surface of the Meikle Water was hardly broken by a gentle breeze from the east.

The 200 odd young trout hatched at the Stronsay School were carried in a basin to the edge of the loch and then transferred into plastic pouches to allow every pupil to release a dozen fish each.

It was a good opportunity to learn about the wildlife with which our trout would be sharing their new habitat: we realised that the tiny alevins would need to be extra careful as many predators such as mergansers, herons, cormorants, eels, otters and even some of the bigger trout wouldn’t mind a little fishy snack! Our alevins would have a more modest diet for the first year, consisting mainly of daphnia, midges at various stages of development, freshwater shrimps and insects.

Pupils gently released the fry in the vicinity of weed beds to provide them with enough cover from predators, after checking the loch water temperature (3⁰C) was as close as possible to the water in which  the alevins had been transported  (4⁰C), in order to avoid thermal shock.

A big thank you to Mrs. Evans who accompanied the children and also to Steve, our janitor who supervised the pupils’ visits to our hatchery on a daily basis over the last couple of months.

Check the video clip by copying and pasting in this link in your browser:

Mr.P

Alevins, St.Andrews Primary, Trout life cycle

St.Andrews fry released in the Burn of Quoykea

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On Tuesday 19th March, the time came to let the small trout go into the Burn of Quoykea, situated within walking distance of the school. Led by Mr. McIntosh, their teacher and Sandy Kerr from the Orkney Trout Fishing Association, who very kindly supervised the project, the Primary 7 pupils were very enthusiastic and knowledgeable, as Sandy’s presentation back in January was still very fresh in their minds. The little burn, in spite of its diminutive size,  remains a crucial watercourse for the reproduction of Orkney sea-trout in the East-Mainland and bringing young people by the burn raises awareness about the importance of its role in the local biodiversity.

Actually, the pupils may well be back in the summer, as Sandy offered to give an electro-fishing demonstration in order to monitor the health and growth of the alevins.

In the meantime, let’s hope the weather improves and that the warmer water brings our fry plenty of food!

Thank you to everybody who helped to make the project happen.

Mr. P

Alevins, General info, Kirkwall Grammar School, Trout life cycle

KGS release their alevins in the Wideford Burn (Inganess)

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The KGS pupils and their teacher releasing the alevins in the Wideford Burn.

It was on March 18th that Mr. Ewing and his dedicated team from KGS met at Inganess Beach to release the  alevins they hatched in the school shed. Spring was in the air and it was a glorious day which seemed just perfect to set the small trout  free in the crystal clear water of the Wideford Burn. This burn not only holds a small population of  brown trout but is also one of the main spawning burns for our migratory sea-trout.  

However, what should have been a great start for the small trout ended in a rather tragic way when last Monday night, merely a week after the fish were released, we were alerted about a severe case of pollution in this very burn. Most if not all of the fish population in the Wideford Burn was wiped out and the source of the pollution is still being investigated. This is a serious blow to the environment but also  to our project as we were planning to come back in June or September to monitor the growth of our trout using electro-fishing equipment.  

One of the casualties of pollution at the Wideford Burn (27/03/12).
Alevins, General info, ova / eggs, Trout life cycle

Hatching Time & ATUs…

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AFYD outing at the Kirbister Loch.
This is a little bit technical but does make sense when you put your mind to it: it is recognised that from the stage of “eyed” ova, brown trout eggs need about 230 ATUs (Accumulated Temperature Units) to hatch into an alevin. 1 ATU = 1 day at a temperature of +1°C or 10 ATUs = 1 day at 10ºC.
The first eyed ova were observed on Stronsay around 20th January and hatched 26 days later; the water temperature in the shed has been averaging +9ºC so, to work out the number of ATUs we just need to apply the formula: number of days x temperature in ºC – 26 x 9 = 234 ATUs
This does explain why the ova at North Walls haven’t hatched yet. The water temperature in the shed there is about 2ºC colder and the eyed ova appeared about the same time (20/01). If we want to know when the eggs are due to hatch, we can use the number of ATUs needed for the eggs on Stronsay to hatch (234) and divide that number by the average water temperature on Hoy (+7ºC): 234 : 7 = 33.4 (about 33 days which is roughly a week later than on Stronsay).
So, as I’m typing this, if everything works according to plan, our alevins must be wriggling out of their shells right now! Don’t forget to look for the foam on the surface which is caused by enzymes breaking down the egg shells.
Let me know about any new developments on Hoy!