Now we are approaching the cooler months of the year in the southern hemisphere and backyard aquaponics guys will be stepping down their barramundi culture and will be starting to look at sourcing rainbow for the winter months.
So, why this change from barramundi to rainbow trout? This is because their temperature requirements are different. In a previous post, I outlined the temperature requirements for barramundi (Lates calcarifer) (link to previous post). But to summarise the findings, the optimal temperature range is 26-32°C and their tolerance range is 15-37°C. This is why they make a good summer crop in Perth and harvesting should be underway.
But what about rainbow trout? In “Fish Vetting Essentials”, we published that the optimal temperature range for rainbow trout is 14-18°C and their tolerance range of 1 – 25°C. The Food and Agriculture Authority (FAO) publishes optimal temperature ranges of 9 – 21°C and a tolerance range of 0 – 27°C (link to source). The Department of Primary Industries Victoria considers the optimum water temperature range is 10 – 22°C and a tolerance range of 0 – 30°C (link to source). The Southern California Edison who published a literature review on (rainbow) Trout Temperature Requirements found that the upper incipient lethal temperature (UILT) for rainbow trout is within the range 25 – 30°C, but were able to maintain weight at 25°C for 30 days (link to source).
The combined experiences of myself and my co-author of “Fish Vetting Essentials” are that the water temperatures in Tasmania this summer (2012/2013) hit 25oC. Whilst it did stress the trout, most survived. We have clients with aquaponics setup who do not experience any signs of ill-health in their rainbow trout until the water temperature exceeds 24-25oC. There was another case at a hatchery in Victoria where most fish survived despite the water temperature reaching 25oC during the summer of 2009.
So, what’s the correct “optimal” and “tolerance” ranges? Well, you’ll have to decide on these based on a combination of literature reviews of natural occurrences and experimental data, and professional experience. Note that the natural optimal and tolerance ranges of any species are a lot wider than their commercial production values. Having revisited my published data, I am staying firm with our published optimal and tolerance temperature ranges for rainbow trout (i.e. optimal as 14-18oC, and tolerance as 1-25oC), although the research shows they can tolerate up to 30oC! I guess that these ranges can be extended or restricted within biological limits, and will also be influenced by genetic differences, other environmental parameters, health and nutrition and so on and so forth.
So, what does all this mean for you? With outdoor pond water temperatures at the moment of below 25oC, the time is about right for stocking rainbow trout, but make sure you monitor the water temperature that it you don’t continue to rear the fish when the water temperatures rise again during late spring.
Survival temperatures are much higher than optimum for intense culture (raceway or circular tanks). Constant temperature water at 15 to 16C, as from a spring (Magic Valley Idaho USA) seems to give maximum growth rate versus Oxygen depletion/disease problems. The limiting factor is the ability to obtain suffient Oxygen through the limited gill area. At these temperatures the Trout, can or should grow about 2 inches (5cm) a month when fed to satiation. This means the body shape (depth to length ratio, sometimes refered to as “condition factor”) becomes very deep, dorsal fin to belly. But the boney head stays the slim shape of a skinney trout. This has consquences: you are feeding a high metabolism fish with the gill area of a fish possibly 1/4 its size! At his growth rate trout will outgrow a happy environment very quickly. “Standard stocking levals” might need to be cut to 25 to 50% to account for conditions. The weight of feed per unit of flow probably should be lower since the fish need all the Oxygen the can use. For a given flow the economical sparsness limit (this the initial leval of stocking that you calculated as being economicaly prudent) might be 50% of the “safe” maximum carrying capacity. At high growth rates the capacity will be reached before you expect. Astute management, anticipating high growth rates, considering decreased Oxygen availablity from fish shape and the temperature is required. This means when the fish weight capacity is reached, the excess half must be removed (processed and frozen), you can’t wait for a sales order.
Moving the fish through the production cycle quickly with fast growth, but fewer of them, can work out to helping the cash flow/morgage pay off consideration, but you need to calculate it out first.
Holding Management to carry the fish through Summer temperatures means training the fish to accept reduced feed (it can help the feed conversion rate) or periodic fasting will help them get through a hot spell. However the potential production is lost. Figure it this way: Your facility Capital and opperation Finacing is costing 5% to 15% a year; the fish could be growing at 1% a day interest compounding daily! Fasting could cost Negative 1% a day compounding daily (2% if you calculate on potential). Fortunatly if the fish are prepared, shrink rates may be considerably less.
For Raceways:
Another option for high temperature trout management is supersaturation of Oxygen. As long as other gases are controlled with Nitrogen below saturation and Carbon Dioxde and Ammonia/Ammonium levels are safely low. Production will work, if the fish’s consumption of Oxygen reduces the out going levels below saturation. Circular tanks might work best here. Air injection or frothing will help but will not suprsaurate Oxygen without supersaturating Nitrogen. Pure Oxygen injection is the only safe way.
For Ponds:
If the water source is colder (higher in Oxygen and Nitrogen) than the production pond, Deaeration is required. Photosynthetic Oxygen production during the day will be equalled by nightime Oxygen consumption. You can not manage high temperature fish growth by the late afternoon Oxygen levels but by somewhere between Morning minimums and average levels. Each weight unit of feed requires the equal weight of Oxygen availabe to the fish. Consideration of a Recirculation Production System should be considered where temperature can be controlled economically (RAS systems were invented for temperature control). Tempering water with a deep in the ground temperature exchange system is an other idea.
Paul Roberts
Aquculture Consultant
316 North 500 West
Brigham UT 84302 USA
435-723-6531
fotbaulpaul@mstar.net
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Thank you Paul for your detailed reply. I like your observation that the fish’s body grows at a faster rate than the rest of its head that the relatively small gill surface area predisposes them to hypoxaemia and all the detrimental effects associated with the condition. Your economic analysis of the situation is very sound. This sort of real life experience cannot be obtained from textbooks.
Thank you very much for your reply.
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From: Susan Kueh
Date: Thu, Apr 11, 2013 at 5:33 PM
hello Richmond & all,
Thanks for getting our think-tank into gear!
The large variation in temperature range quoted maybe because the temperature is not the direct ‘killer’, rather something underlying as you pointed out together with temperature extremes or, perhaps something that temperature affects, such as oxygen – trout is a fast swimmer, there requires more oxygen. And barra kept in seawater may be more affected with temp extremes, as oxygen levels are lower in seawater at any temperature. So perhaps with more research, a ‘temperature-oxygen number’ could be generated, same as degree days for drug withdrawal.
Hope to hear from the rest, Susan
Susan Gibson-Kueh BVSc, MSc (Aquatic Vet. Studies)
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See also this link – http://www.fish.wa.gov.au/Species/Rainbow-Trout/Pages/default.aspx.
Rainbow trout is a coldwater species inhabiting freshwater creeks, dams, rivers and lakes. It thrives at 5-20ºC but there are mortalities once water temperature increases to 26-27ºC. However, the trout produced at PFRC are unique because they have adapted to withstand the higher temperatures of local conditions.
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