After a morning spent trying to catch some more broodstock with Carlos and Daniel from Achotines Bay, we headed back to catch up with the RSMAS students as they got ready to depart, writes Alex Mühlhölzl. Myself and John Hutapea were the only two remaining workshop members for Thursday afternoon and Friday.
The group had completed the 48 hour transport trial stage in the morning, and had done a count out on the larvae to calculate the survival rates. The 10,000 larvae shipment had a survival rate of 22 per cent with the higher density 40,000 shipment having a lower 16 per cent survival rate. Both of these shipments were in 20 litres of water and by hour 48 the water temperature was at ambient temperature of 25.5 degrees.
This afternoon John and I spent time working on our own reports on the course as well as comparing notes on our own individual projects. I gave a few ideas on broodstock anti-walling to John and look forward to hearing from him as to how successful they are upon his return to Indonesia.
The spare time this afternoon gave me a chance to see some of the more detailed management work that goes on behind the scenes to keep everything running, and got to see the full broodstock water analysis work that happens several times a week. The results were logged and were all consistent with the previous readings and were well within the acceptable parameters needed for the health of the broodstock.
We also started to see visual signs of walling with the juvenile tuna. Now at 35+ days the tuna still seemed tentative in taking artificial feed preferring to hunt the tank for live feed. At dusk we could see and hear the juveniles colliding with the tank walls with some of them displaying visual evidence that they had suffered wall collisions. With a stock of 50+ juveniles the fact that there had only been one mortality was a good sign, however the walling issue was becoming more prevalent as the fish grew in size.
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