Here at C.E. Fish Essentials, we receive questions upon questions daily about the best products, best way to feed fish and occasionally a question or two from the more scientifically literate about digestion. Finding ways to improve nutritional uptake and digestion in ornamental fish species is central to the core ethos of our company. In fact, it’s what sets us apart from all the rest; that being said, it is not easy to devise new and inventive ways for fish to absorb nutrients!
One of my key ‘fish nutrition’ interests as of late has been the connection between mental stimuli and digestive processes that occur as a result of taste, smell and more interestingly for me, visual stimuli. Much like when our stomach grumbles at the smell of bakery goods or we salivate at the sight of a succulent steak, our minds are programmed to prepare our digestive systems for the influx of food materials and this is not exclusive to humans, fish do it too!
This preparative biochemical action by the brain on behalf of the digestive system is known as the cephalic stage; ‘cephalic’ arising from the Greek word κεφάλη (pronounced ‘kefali’), meaning ‘head’. The head stage of digestion is usually initiated by one or more of three contributing sensations, namely, olfaction (sense of smell), gustation (taste) or visual stimulation. These sensations evoke the release of various neurotransmitters, e.g. acetylcholine which act on both the sympathetic and parasympathetic nervous systems to initiate digestive reflexes, one of which being the secretion of oesophageal mucus to line and lubricate the throat. As fish do not possess salivary glands, it is this mucus which acts to aid motility of food through into the gastrointestinal tract for digestion. Other secretions directly influenced by cephalic stimuli are those of hormones such as insulin and the catecholamines, these hormones are responsible for various neurological responses, notably the regulation and breakdown of lipids / fats (lipolysis), respectively.
Science jargon aside, I am inferring that;
1. Fish are like us, their bellies grumble & they ‘salivate’ when they see, smell or taste food
2. We can do certain things to initiate the cephalic stage (and assist digestion).
Some fish keepers tap the aquarium lid before feeding; I personally use a hand signal (waving my fingers at the fish), but there are endless options. The key things are that it is consistent (e.g. you do it every time you feed) and you do it a short time before feeding so the fish associate that action with food. At first, you may want to do it immediately before feeding for a period of time (it usually takes only a few days for fish to understand what it means), then as they learn, you can begin to increase the waiting time between your indication that it is ‘dinner time’ and the actual feeding. This form of classical conditioning is known as conditioned hunger or “the appetizer effect”, where a neutral stimulus such as a hand signal to your fish (or the dinner bell at school) can stimulate the involuntary digestive responses which aid and support effective digestion.
Photo: James Leagas ©