Mullet, unlike the rest, are just and mild,
No fish they harm, by them no seas are spoil'd;
Not on their own nor different kinds they prey,
But equal laws of common right obey.
Undreaded they with guiltless pleasure feed,
On fattening slime, or bite sea-grown weed.
(0ppion.)

Grey Mullet in the Aquarium

by John B. Clark, B.Sc.
First published in http://www.smartgroups.com/groups/Euromarines
Aquarticles

   In recent years marine fishkeeping has received a well deserved boost in popularity. Today there are many shops that stock marine tropical fishes in quite a wide variety, and there are many books which tell us how to look after them, and yet we still seem to know very little about our own native marine fishes.        We have amongst our British fauna a large number of marine fishes that can be kept quite successfully in the aquarium, and many of these are also suited for tropical community conditions, but there is very little written information on the subject. Most of the popular books on British marine fishes are of very little help and are mainly aimed at anglers. In many cases the information given is incorrect, as also are some of the drawings. Mistakes seem to have been copied blindly and it is quite obvious that many so called authorities have never seen their subjects.
   I shall try to give a little relevant information on a small group of British fishes, the Grey Mullets. Small specimens of these are excellent aquarium fishes and are ideal for the beginner learning the ways of a marine aquarium before graduating to the exotic and expensive. 'I'he well established expert will also find them ideal, because they perform so many important functions in the aquarium that few other fishes can do with such efficiency. =    Throughout the world there are more than 100 species of Grey Mullet, over half of which belong to the genus Mugil. Most inhabit tropical seas but there are a few temperate species. From British waters at least three species have been reported: Mugil labiosus (thick-lipped Grey Mullet); Mugil ramada (thin-lipped Grey Mullet); Mugil auratus (golden Grey Mullet).
   M. labiosus is by far the commonest species. These fishes all grow to a fairly large size, 2 feet or more. They are fished for commercially and are frequently seen on the fishmonger's slab (incidentally they are excellent to eat). In the past, they have been specially cultured in artificial ponds to supply the tables of noblemen in the Mediterranean region.
   Grey Mullet are not closely related to Red Mullet. They are, however, quite closely related to the sand smelt (Atherina), with which young specimens can easily be confused. The major distinguishing character is that Grey Mullet have four spines in their first dorsal whereas sand smelts have more than four.     Unfortunately there is little variation between the different species of Grey Mullet and hence little satisfaction would be gained from keeping together more than one species. In any case one would really need to be an expert to identify the different species with certainty, but, not to worry, they all mix with the greatest of harmony.
   All the British species are the typical fusiform fish shape with a wedge-shaped snout terminated by a broad mouth which cannot be opened very wide. The lower jaw bears a central peg which fits into a socket in the upper jaw. The lips are well developed and are used extensively in feeding. All the fins are of moderate size. The pectorals are set high on the body and tend to point upwards. There are two dorsals, the first of which is spiny, with three spines all arising together at the anterior end and the fourth weaker spine sets a little farther back. Most of the time the first dorsal is folded and fits into a depression on the back, giving a streamlined contour. The background colouring of these fish is mainly silver grey. Dorsally on each side there is a prominent greenish or golden iridescent stripe and the flanks are traversed by longitudinal stripes produced by a dark spot on each scale.
   Not quite as attractive as many of the tropical marine fishes, but nevertheless a very useful fish in the marine aquarium and exceedingly easy to keep. In any marine set-up there should be room for a few Grey Mullet, since they are one of the best marine scavengers that one could ever find. Constantly in motion, they flash up and down sampling anything that might be edible. This includes cleaning rocks, plants and glass in batch fashion and also the bottom.

   Anyone who has kept marines will know that sometimes there are tremendous fluctuations in bacterial numbers, resulting in a very rapid lowering of pH and oxygen content. More often than not this is caused through uneaten food but there are many other reasons. Often one realises too late that something is wrong and within a few hours a tank full of expensive fishes can be dead. This is one of the hazards of keeping marines, and it has resulted in many people giving up or not starting to keep marines.
   Grey Mullet are typically coastal fishes and therefore run the risk of being trapped in tidal pools by the ebbing tide. Unlike the open oceans these smallish bodies of water can rapidly change their temperature, salinity, pH and oxygen content, while the tide is out. Grey Mullet also frequent estuaries and even penetrate into fresh water at times. These fishes can, and do tolerate very changeable environmental conditions. Like rock pool fishes, and also the majority of freshwater fishes, they possess a mechanism for coping with foul conditions. The commonest mechanism in littoral fishes is simply to leave the water temporarily and utilise the atmospheric gases. No doubt they would probably prefer to do as Mullet and the majority of freshwater fishes do, which is to surface and mouth the atmosphere, but unfortunately most littoral fish lack a swim bladder and would use a lot of energy staying at the surface, thus defeating any benefit gained. Most of the tropical marine fishes which we can buy in this country come from open waters where conditions are rather stable and thus they do not need to be able to fight adverse water conditions, and many cannot. When oxygen is lacking few tropical marine fishes will rise to the surface to mouth the atmosphere. If they do their efforts are generally very feeble. Most seem to grin and bear it, perhaps hoping that the stupid idiot staring through the glass at them will do something before adding them to his (or her) obituary. Grey Mullet, probably because they are a very active fish, are soon affected by an oxygen deficit and rise to the surface, still swiftly swimming around, and mouth the air long before conditions have grown serious for most other fishes. Incidentally they will still be swimming around, long after all the other fishes are dead! So efficient is their adaptation that in the past I have had them swimming around in putrid water containing rotting seaweed, which proved to be of pH 6.2.
   As far as temperature requirements are concerned, the species are not fussy. They thrive equally in cold water or tropical conditions. Owing to a thermostat which short-circuited I once had survive the ridiculous temperature of 117º F, which wiped out a lot of tropical marine fishes. Although temperate fish, they do seem to enjoy warmth. My fish are kept in a tank with tropicals 68º F (20º.C) and during the night their resting place is huddled above the heater.
   British species are also indifferent to changes in anything from neat sea water to fresh water systems, but they do not thrive very well in completely fresh water, tending to become rather sluggish and pale in colour; however, a small quantity of salt soon 'perks' them up.
   During the night Grey Mullet rest just above the bottom, usually grouped together head to tail. Although they do not move bodily in the water in this condition, their pectoral and caudal fins are continually in motion and the tail half of the fish is always folded around the side of the body in a most awkward-looking fashion. If the lights are switched on it takes them a good ten minutes or more to wake up, provided that they are not otherwise disturbed. Although Mullet are not likely to attack other fishes they are rather prone to have their own fins nipped. This takes place mainly at night, probably when they are sleeping. During the day they seem to have enough speed to escape from aggressive characters. The favourite morsel seems to be the lower lobe of the tail, which gives them a very shark-like appearance when it has been reduced. Luckily they are very fast to regenerate damaged fins.

   Fungus Infection:  These fishes seem to be immune to marine 'white spot' disease, since I have never found a specimen with this ailment, even when the rest of the fishes in the tank are heavily infected. They are very susceptible to fungal infections of the body and fins, and parasitic copepods, both of which may result in the loss of scales. Both these infections are easily cured by a simple freshwater treatment by placing them directly into fresh water (if they are kept in sea water) and keeping them there for 2 or 3 days. The fishes can survive this rather drastic change but the infective agents are killed. A fish in very bad condition may not be able to stand this treatment and it may be necessary to add some salt (or sea water) to the fresh water after an hour or so to relieve the stress. One can use judgement as to whether this will be necessary or not by the reaction of the fish. After 2 hours a fish has normally quite well adjusted to the new conditions. Alternatively methylene blue or potassium permanganate can be used in fresh water or dilute sea water. Copper sulphate should not be used since they are very susceptible to copper poisoning.    Grey Mullet are not often seen in the shops, but periodically they can be sometimes obtained from commercial sources. The easiest way of obtaining them is to go and collect them. From the middle of summer to the end of winter small specimens are often found trapped in the larger rock pools around most of our coast. In summer they appear as small fry about a half inch long and by the end of winter they have reached about 2 in. long. Occasionally larger specimens are found, about 4-5 in. long, which represent the previous year's generation. Whenever they are found they are quite numerous since they are a shoaling fish.
   To catch them a large net is required and a little patience. This is not a fish which one chases to catch. They move fast and are good at hiding. A sudden movement will result in the shoal dispersing in all directions, making it very difficult to select a single fish to follow and net. The best method of catching them is to leave a large net immersed in an area that a shoal is known to frequent, wait quietly until they assemble over the net and then raise it slowly until near the surface, when it must be lifted well clear since when first trapped they try to jump over the sides of the net but soon resign to their fate. This habit of jumping over a net is troublesome in commercial fishing since once one fish leads the way the rest follow. In the past this trouble has been overcome by sprinkling straw on the water inside the net and the fish try to jump over the straw, thinking that it is the edge of the net and in doing so expend their energy.
The fish can be caught quite easily during the day, but I prefer to catch them at night, going armed with a strong flashlight, when they can be found in groups in the deeper parts of the pools in their static sleeping posture and they can be netted more easily.
   They travel very well and require only a small quantity of water. They settle down very rapidly in the aquarium and will start to eat dry food within minutes of introduction. At first one would think that their appetites are insatiable since they will continue eating as long as food is available and will rapidly put on weight, so one must learn to limit their daily intake, since fat fish do not make good scavengers. In a community tank it is advisable to add all the food necessary in a large quantity and not in small amounts, hoping to satisfy the Mullet first before feeding the other fishes, since they are always the first to the food. Placing all the food in together allows the other fishes to get their share before the Mullet can devour it all.
   I have kept Mullet for some time now and although they are not the most beautiful of fish I would not wish to be without them.