Interdisciplinary Project on Climate change in Tropical Aquaculture (iAQUA)

Project summary

To understand how global warming will affect tropical aquaculture, we will study how a temperature rise from the current value of 27-32 °C to 32-37 °C will affect physiological performance, food conversion efficiency and growth in air-breathing fish. Particular emphasis will be placed on the role of the cardio-respiratory and digestive systems to address the prevailing hypothesis that compromised oxygen transport capacity determines temperature tolerance of aquatic ectothermic vertebrates.
4 air-breathing fish of importance in tropical aquaculture (pangasius, snakehead, climbing perch and rice eel) with marked differences in structure and function of their gills, air-breathing organs and cardiovascular systems have been selected. By correlating temperature sensitivities, physiological functions and anatomical structures, we will identify physiological bottlenecks and key-adaptations that allow some species to thrive, while others perish, in face of environmental change.  Thus providing an essential basis for future decision making in light of climate change.

The capacity to continue this research beyond the time frame of the project (PhD's and Facilities) will be established in Can Tho. Further, an International annual PhD course on the physiology of air-breathing fish will be established at Can Tho University employing modern teaching techniques. This course will place emphasis on training young researches from universities in Southeast Asia (Indonesia, Bangladesh etc.).

Outputs

Project completion report:

The project exceeded most of its objectives. We planned for 1 Danish PhD and 4 Vietnamese, but end up with 2 Danish (due to kind funding from Faculty of Science and Technology at AU) and with 5 Vietnamese PhD. We aimed for 25 publications in international peer reviewed journals but have ended with 33 published and several more in line for publication as well as 19 Vietnamese journal publications. The international journals are all highly respected in the fields of comparative physiology, fish biology and aquaculture and many of these publications are in top journals such as Physiology, Journal of Experimental Biology and Aquatic Toxicology. We have also been very busy presenting our findings at International and National conferences and workshops and here also have exceeded our promised outputs substantially.

There were two main research goals within the iAQUA project:
1.To set in place a capacity for advanced respiratory physiology research at CTU.
2.To examine the effects of temperature elevations on the respiratory aspects of air-breathing fish from the Mekong delta, chosen for their importance in the aquaculture industry Our initial hypothesis was that we would either see no effect or a negative effect of elevating water temperature above the present level. We set into place an extensive range of experiments examining the effects of temperature and were met with very surprising results:

We found that the temperature elevations forecast for the next century in the region are, in isolation, unlikely to negatively impact the chosen air-breathing fish species (Pangasionodon hypophthalmus, Chitala ornata and Monopterus albus). This conclusion was based on a wide range of studies spanning studies of circulatory system morphology and regulation, respiratory surface quantitative morphology, blood oxygen binding and transport characteristics, and oxygen uptake and partitioning between air and water phase. In addition, growth and feed conversion efficiency (FCR) studies were performed over long periods in the same temperature regimes. The wide range of these findings, all pointed to the same conclusion and we have considerable confidence in its validity. In particular, we found that it was possible to reduce the current industry FCR from its present 1.6 to around 1.1, which represents a very significant potential saving for farm production costs. This may well provide the economic incentive for technology investment in water quality.

On a more basic science level we made several exciting discoveries, including:
+Discovery of the first teleost fish showing convincing air-breathing control linked to blood carbon dioxide levels. This result highlights the transitionary position of these animals between water and air-breathers.
+Discovery of the role of lactic acid in the stimulation of air-breathing.
+A surprising plasticity in the respiratory surfaces linked to both environmental temperature, environmental oxygen and the activity level of the animal itself.
+The discovery of the mechanisms underlying the extraordinary pH regulatory ability of these animals.

Brief popularized abstract:

The Mekong delta in southern Vietnam houses a huge aquaculture production with global export of household names. Notable among these products are air-breathing fish including the well-known Pangasius. These air-breathing fish can breathe both air and water and their physiology makes it very difficult to predict reactions to stressors based on knowledge garnered from water-breathers. The main purpose of iAQUA was to establish a capacity for research in fish respiratory physiology and use this to understand the impact of increasing environmental temperatures on these animals. We examined the impact of temperature elevation on a wide variety of aspects of their respiratory physiology, as well as on their growth and their food conversion efficiency. Surprisingly, we found significant benefits to the temperature elevations expected within the next century across all parameters. Indeed the improvements in growth and food conversion efficiency that we discovered are so large that they hold the potential to for significant savings in production costs as well as improved well-being and product quality. Researchers in Vietnam are now examining ways to achieve controlled temperature elevations in order to take advantage of this improved growth efficiency.

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