Natural Growth Promoters in Fish

Saponins are naturally-occurring defense compounds produced in some species of plant, and while most nutritionists off the top of their head would tell you that feeding them to fish is probably a bad idea, new evidence has suggested otherwise.  Recent experiments have found that cultured carp and tilapia fed a small level of saponins in their diet experienced increased growth rates and lower oxygen demands than fish fed a normal diet.  Upon closer examination, it was concluded that saponins help the digestive tract of the fish take up dietary components, as well as stimulate the activity of digestive enzymes: both of these effects lead to an increase in feed utilization and efficiency of uptake, and thus better growth rates.

This has some massive implications for the aquaculture industry: the use of synthetic growth promoters such as antibiotics or steroid hormones is experiencing more and more resistance from consumers and industry alike, and rightly so.  These compounds are not natural and their effects on the fish (and the people who eat that fish) are still being studied.  However, saponins are natural, plant-based, renewable compounds, making them a seemingly more healthy and sustainable option for a feed additive.  

‘Four Fish’: A Crash Course in Sustainability

I recently finished reading Paul Greenberg’s ‘Four Fish’, a book that looks at four of the main fish species in the human diet and analyzes them from a historical, economic, and sustainable perspective. In addition to being a great read, the book made some important points as to the future directions that we should be taking regarding these species.

The fish covered are salmon, bass, cod, and tuna. Greenberg delves into the fishing history of these species and shows how each one is closely tied to human diets and economies. He then discusses their future prospects with respect to continued fishing as well as aquaculture.

Essentially, his message is clear: we are fishing these animals too heavily, and we need to rely more on farming. However, he accurately points out that, like current fishing pressures, many current farming practices are also unsustainable. He calls for a revamping of the aquaculture industry by such methods as farming fish that have lower feed conversion ratios, as well as adopting more sustainable management practices such as polyculture.

Overall, this is a must-read book for anyone interested in the future of seafood!

MSc Module 2: Aquatic Animals and the Environment

The second two-week module in the Sustainable Aquaculture MSc program at Stirling was titled ‘Aquatic Animals and the Environment’. It covered the different environments where aquaculture is carried out, with a focus on physio-chemical processes, community structure and function, and environmental impacts and remediation.

The first two days of the module were lectures given by Trevor Telfer on a variety of different topics, including inland and marine systems, the basics of environmental impact, and different factors affecting water quality. These lectures were given to prepare our class for our first field exercise, which was a site visit to Howietoun Fish Farm (see previous blog article). There, we conducted experiments and took water samples to analyze the impacts that the farm was having on the environment.

This analysis took place on Thursday, when we spent the entire day in the laboratory. In the morning, we analyzed the water samples for a number of different parameters, including alkalinity, conductivity, nutrients levels, and suspended solids. The results of this chemical analysis helped us to determine the overall water quality at different locations around the farm, which in turn allowed us to comment on the environmental impact of the facility. In the afternoon, we analyzed the biological samples, identifying plankton in water samples and going through sediment to find and identify different invertebrates.

The second week was spent in the field at Campbeltown (see previous blog article). There we completed an in-field exercise in aquaculture site selection, taking into account all the different factors that affect the decision of where to put a fish farm and what to grow there. This experience was invaluable, as we were given the opportunity to actually look around, test the water, and then make a decision and defend it. Plus, it was our first overnight trip and even though there was a lot of work, it was a blast!

Overall, I am greatly enjoying my experience here at Stirling, and I hope to continue learning as much as I have over the past month. The next module is Aquatic Animal Nutrition and Food Safety, and while there is no field work associated with this module, it should still provide interesting and valuable.

4-Day Field Exercise: Aquaculture Potential of Campbeltown Loch

Salmon farm in Loch Fyne

This week our MSc class loaded onto two minibuses and drove 4 hours from Stirling to Campbeltown Loch, a small bay on the west coast of Scotland. There, we conducted a field exercise in aquaculture site selection, attempting to take all the different biological, environmental, and social factors into account and select an appropriate fish farming site within the loch.

On the drive up on Monday, we visited a commercial salmon farm in Loch Fyne. At this facility, state-of-the-art underwater cameras are used to monitor the fish during feeding: a computer program monitors the fish and recognizes uneaten food pellets falling past the camera. When this occurs, the computer automatically shuts off the feeders, preventing the release the excess food and minimizing the environmental and economic loss associated with this problem.

On Tuesday, we split into small groups to conduct field work in the morning. We went out on the loch in boats to take water and sediment samples, as well as monitor the currents using drogues and GPS positioning equipment. Additionally, we toured the coastal town to discuss the social impacts of an aquaculture site on the local economy. The objective of the exercise was to distill the information gathered and select a site within the loch for an aquaculture venture. In our groups, we were to select a site, choose a species to farm, and then defend our decisions in front of the class and our professors. This group work, and the resulting presentation, was done on Wednesday.

Tuesday afternoon we were given the opportunity to tour the Machrihanish Fish Farm, another commercial and research facility owned and operated by the University of Stirling. Here, we saw their revolutionary wrasse program, where they are growing cleaner wrasse to be used as biological pesticides of sea lice in salmon cages. The wrasse eat the lice directly off the salmon, reducing the need for chemicals in the environment. Additionally, there is some evidence to suggest that the wrasse eat bio-fouling organisms off the nets, adding an additional level of value to their use!

Loch Fyne Oyster Farm

Thursday we returned to Stirling, but on the way stopped at a salmon hatchery, as well as an oyster and mussel farm. These visits were very enlightening, and gave us some exposure to the wider aspects of the aquaculture industry in Scotland.

Overall, the trip was incredibly valuable, as this was a real-world scenario and we were given direct access to the site. We discovered that it is difficult to balance all the factors involved in site selection, but in the end the six different groups all produced six different viable ventures!

Site Visit: Howietoun Fish Farm

This week our MSc class got the opportunity to visit Howietoun Fish Farm, a commercial and research facility owned and operated by the Institute of Aquaculture. At this site, there is a hatchery for brown trout (Salmo trutta) and Atlantic salmon (Salmo salar), as well as a smolting unit for salmon and a fishery for brown trout.

This visit was during our module on ‘Aquaculture and the Environment’, and as such our focus was on the environmental impacts associated with the fish farm. The facility is fed from a stream that runs through the area, and so we started by looking at the entire catchment to help determine the quality of water running into the farm. We then visited the farm itself, touring all three units in detail.

We took water samples to analyze for different water quality parameters, as well as measurements of the physical characteristics of the water (dissolved oxygen, temperature, and oxygen saturation). Additionally, we took biological samples in the forms of plankton tows, kick samples, and sediment grabs. All this data will be synthesized back at the Institute and the assessment for this module will be based on a group presentation, as well as individual reports, focusing on this information.

The tour started in the hatchery, were we covered spawning techniques and egg husbandry for both brown trout and Atlantic salmon. We then moved to the smolting unit, where salmon are prepared to make the transition from the freshwater they were born in to the saltwater where they will spend a majority of their lives. Finally, we visited the fishery for brown trout, where the fish are kept in large earthen ponds until they reach a size suitable for stocking sportfishing waters.

It was a very interesting tour, and it was really cool to see some of the practices we have discussed in class put into action. It will also be interesting to work up the samples that we obtained, as that is the only way to determine what sort of impacts the operation is having on the surrounding environment.