kj23502
lazy dayz
I've been wondering what exactly the proper terms mean just to know, I guess. I did a search and came across this. It's also written by an Andywg....our Andywg?? 
http
/www.bsacforum.co.uk/forums/archive/...php/t-7760.html
http
/www.bsacforum.co.uk/forums/archive/...php/t-7760.htmlBeing a member of fishkeeping forums I often came across the words fish, fishes, shoal and school. Many people are a little unaware of their correct usage.
The differences between the first two are probably better known:
Fish can mean an individual fish, or many fish of the same species
Fishes refers to a group of fish comprising of more than one species.
The below is something I wrote a while ago to inform people of the actual scientific use of the terms. Happy reading:
Many people (myself included) tend to use the terms "school" and "shoal" somewhat indiscriminately without thinking too much for the difference between them.
However, I happened to come across the scientific definitions while reading.
The below information was gleaned from Fishes, An Introduction to Ichthyology Fifth Edition by Peter B. Moyle and Joseph J. Cech, Jr.
Shoaling is perhaps the most fascinating social behaviour possessed by fish, although most attention has been focused on the most spectacular aspect of shoaling: schooling. A School of fish often seems to have a mind of its own, moving in co-ordinated fashion through complicated manoeuvres with the members precisely spaced within it. A shoal is any group of fishes that remains together for social reasons, whereas a school is a polarised, synchronised shoal (Pitcher and Parish 1993)
The distinction is necessary because experiments have shown that schooling is just an extreme example of many shoaling behaviours. It is important also to note that fish shift in and out of schools on a regular basis.
A shoal can go from the classic grouping of fish into an amorphous mass in a matter of seconds. The stimulus for this is a change of activity from travelling, feeding, resting, or avoiding predators. The shape of a shoal can vary widely depending on activity and type of fish; fast moving shoals typically assume a wedge shape whereas feeding shoals are more or less circular.
Shaw (1978) estimated that 25% of fish shoal throughout their lives and that approximately half of all fishes spend at least part of their lives shoaling. In many commercial species the largest shoals are formed when a number of smaller shoals merge. Radakov (1972) mentions “chains” of shoals of migrating mullet (Mugil)in the Caspian Sea that were 100km long! Radakov further noted that in the North Atlantic, herring shoals can occupy 279 million to 4,850 million cubic metres with a fish density of 0.5 to 1.0 fish/cubic metre. That's almost 3 billion fish in one group
How do fish school?
Schooling requires precise sensory contacts among individuals within the schools. The fact that most schools (but not shoals) disperse after dark indicates that vision plays an important part in schooling. Laboratory experiments with temporarily blinded fish support this, but also show that other senses are used. It is believed that the lateral-line system (seeing as it is so sensitive to the movement of water) also plays an important part in ensuring the fish in a school maintain their spacing. It is also believed possible that sound or pheromones play a part but at this time there is no evidence to support this.
Why do fish shoal?
Landa (1998) argues that the combined effects of the below benefits of shoaling provide strong selective incentives for fish to join shoals.
1) Increased Hydrodynamic Efficiency
This applies mainly to schooling fish and is appealing both because of the regular spacing of fish in schools and because shoals tend to be uniform in size (Hoare et al. 2000). However, laboratory experiments have not shown the positioning of fish in schools to gain any advantage from the hydrodynamic lift created by their neighbours (Pitcher and Parish 1993) though it is still believed that this is the case in the wild. Landa (1998) argues that the leadership of a school is always changing, because while being immersed in a school incurs hydrodynamic advantages to individuals, being the leader of a school means you are the first to food.
2) Increased Efficiency of Food Finding
The reason for this is the presence of many eyes searching for the food. Fish in shoals “share” information by monitoring each other’s behaviour closely. Feeding behaviour in one fish quickly stimulates food-searching behaviour in others (Pitcher and Parish 1993)
3) Increased Reproductive Success
Little energy has to be expended to find a mate within a shoal. Also, for migrating spawners that travel long distances it is more likely that the average direction taken by a shoal is better than one taken by a single migrating fish.
4) Reduced Risk of Predation
This comes in two main interacting ways: dilution, and confusion (Pitcher and Parish 1993). The dilution effect relies simply on safety in numbers (Pitcher and Parish 1993). In any given attack, a smaller percentage of a large shoal will be eaten compared to a small shoal (Major 1978).
The confusion effect is based in the common observation that shoaling fish tend to get eaten mostly when they have been separated from the shoal. Shoaling fish are the same size and silvery, so it is difficult for a visually oriented predator to pick an individual out of a mass of twisting, flashing fish and then have enough time to grab its prey before it disappears into the shoal.
There is plenty more in the book on this subject (begins on page 192) and also in Biology of Fishes by Carl E. Bond (Second Edition).
And my sincere congratulations to any divers who managed to get to the bottom without falling asleep
Andy
