One of the most interesting discussions I found take place at the reef geek convention MACNA was regarding water temperature and the fish we love to keep. As more and more deepwater fish are coming into the industry their cool temperature requirement is also becoming better understood–but it’s not just these deepwater fish that seem [...]
One of the most interesting discussions I found take place at the reef geek convention MACNA was regarding water temperature and the fish we love to keep. As more and more deepwater fish are coming into the industry their cool temperature requirement is also becoming better understood–but it’s not just these deepwater fish that seem to benefit from the mid to low 70 temperatures. Many reef fish that are typically found in 80 degree water in their natural habitat have been noted to thrive and improve in health at cooler temperatures.
Fish are ecothermic, meaning they rely on the temperature of the water they live in for their own body temperature which has a positive correlation with their metabolism. Lower water temperature slows the metabolic processes and, generally speaking, less oxygen is used while more oxygen is available in the water–that is because oxygen solubility increases as water temperature drops.
Matt Wittenrich’s MACNA talk shined an intense spotlight on the role temperature can play in fish breeding. He compared the larval development and mortality rates of larval fish at different temperatures. Hopefully these poor photographs, but interesting slides will book Matt a few speaking engagements. Even for the non-breeder his dialogue on captive breeding was captivating and educational.
Matt’s slide above shows the same species at the same age–yet when kept at 78F the overall size and jaw structure is much more developed and mortality rates (curve to the right) are much less (x axis = time, y axis = living fish) than those kept at 81F. When larvae are maintained at lower temperatures they hatch out significantly larger making it easier for them to feed and survive. This occurs because lower temperatures reduce metabolic rates so that better absorption of limited food occurs. The relationship between temperature and metabolism in fish and ectotherms has been well studied. Matt did a great job of touching on this past work and presenting his first hand information and experiences in a clear and easy to follow manner.
Some noted aquarists have observed an increase in health with tropical reef species such as anthias, angelfish and butterflyfish when kept at the mid to low 70s. There seems to be a logical link between metabolic rates and feeding frequency that aquarists will learn to better balance in the future with temperature. In the wild fish have the opportunity to eat large volumes of food throughout the day. For example, a small Chromis or Damselfish has been found to eat the equivalent of nearly one cube of frozen prepared food in a single day in the wild!
Even with modern aquarium filtration methods it is impossible for most aquarists to feed that much. Temperature may help bridge this gap in feeding frequency and volume that we see in captivity vs. the wild. These are just my thoughts based on my own anecdotal observations and those from other industry professionals. It is an area that must be explored and studied, and I believe it will. Understanding the nutritional needs and metabolic processes in ornamental marine fish is critical for their long term care.
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