MARINE NATURE NOTES

Otago Daily Times, Issue 21940, 29 April 1933, Page 15

MARINE NATURE NOTES

Written for the Otago Daily Times. By David -H. Graham, F.Z.S. FISH AS FCOD FOR FISH. The subject of the food of fish is one N that will crop up in fishery research -till the end of time. Fish as a rule feed on many other forms of sea life besides fish. ' There are certain species that do mot devour any. food but crustaceans; others’ again nothing else but shellfish, but this article relates solely to fish feeding on fish. The habits of fish which feed on the animals lower' in the - scheme of Nature are surprising, and in some instances the writer has found that these fish are more or less related and adapted to the mode of life of the particular food that is eaten. I have numerous instances of fish feeding on one .particular food for a limited period and then changing to a totally different form of sea life and feeding on that alone for weeks. Fishes. feeding ; in the sea and seeking food either on, at; or near the . surface or along the. floor of the ocean, could easily be compared to a flock of 'birds which feed on insects, worms, and other forms on the land. _ There is, however,- an interesting distinction between those fish which almost confine themselves to fish as food and those which feed upon the lower organisms and creatures. But withal, the division is not complete as there are fish which feed upon other fishes, and some that do not devour fish at all, While the general run of fishes take a mixed diet which includes fish, ' crabs, shellfish, worms, coral, and sea- ■ weed.' , ■ ' The most important and, to me, the most interesting part of a work which I, have just completed relating to my findings while at the marine station at Por- . tobello, concerns the food found in the stomachs. Of fish that, feed on fish, I find that 41 species devour no fewer than 43 distinct species. I am fully convinced that, if this research could have been prolonged, possibly 80 or 90 per cent., of them would have been found feeding on fish. The familiar red cod, as was expected, devoured the greatest variety of fish. No fewer than 27 species of fish were identified by the writer from their stomachs. No doubt further examinations will enlarge this number, as the red S cod are ever ready to prey on anything that moves or is moving in the sea. All “ : ' ! t*ies of fish were'eaten—from fiat fish , such as flounders and soles, which live on the floor of the ocean, to those fish ■uch as " Maori Chief ” and taumaka which restrict their habitat to rocky situations, find to roving fish such as mackerel, garfish, and even dogfish in the small stages. Red cod was the only fish that I found feeding on elephant fish. It is not 6urprising to find juvenile red cod m the stomachs of adults. Speaking generally, the red cod is, of course, a gi'oss feeder, end is unsurpassed in greediness and ferocity, and nothing comes amiss to its insatiable maw. From my observations in the ponds and tanks at the station i estimated that a red cod will consume in one day its own weight of food, thus showing how great its appetite must be and its rapid digestive powers. Fish are its popular diet when it is roving and moving in shoals outside the harbou , these are seized and swallowed head first. As soon as a victim is within sight Jhe red cod is seen ter move with,a sudden rush, and, withamazing rapidity, the victim disappears. Cannibalism in fas is not rare, but the red cod is the one and only fish to my ' knowledge that habitually devours its smaller and younger, - with the next greatest number of species to its list is the blue Although it is not a rover m the same manner as the red cod, no fewer than L> species of fish, including those of its own species, were found in the stomachs o blue cod, and ou examination 6 howed that most of the prey inhabited rocky situations. Groper was found to feed on 11 species of fish, including an occasional small -one of their- own ? peciesThe food of the groper goes to pro>e that the mackerel must be more abundant in deeper waters than we realise, as they are frequently found in gropers stomachs at all times of the year, including those periods when groper migrate or move inshore and back again to 80 and 100 fathoms. It is common belief „ tha A t So mackerel disappeared from? e ro J?hen» coast on the appearance of the southern kingfish, but -the finding of mackerel in the stomach of groper and Porbeagle sharks, goes to Jirove that mackerel axe still.in our water. Just why they are not seen close inshore is a problem to l.’lie barracoota, which is a fast moving fish and continually °n. the ’^ e ’ found to devour 10 specnes of fish, of them being rovers, and the other two rock-inhabiting fish. I no iced that he barracouta devoured the ling and the liner devoured the barracoota, but did not apparently prey on their own kind. In numerous instances fish vertebrae found iu the stomachs of a number ot fish that were uifidentifiable, or could be only guessed at, and I always refrained from recording my guess. In many instances I found small fish less than three inches in length and difficult to piove with certainty, although I could often recognise the family to which they belonged. ■ *' The rock-loving Maori Chief preyed on • eight species of fish and, strange to re-late,-the following roving fish were found in their stomachs;— Sprat, red cod, ahuru, opalfish, ling, and ' red gurnard., J h ■ •was surprising as the Maori Chief is never caught i away from rocky parte_of the coastline. Then again, I found sand - flounders, 11 inches in length, m their stomach, so. that they must wander moie th The 9 skate° S which inhabits the sandy situations of-the sea, also. feed on eight species of fish, four of which are ove s and fast moving, viz., sprats red cod, ahuru and opal fish. Just how those alow-moving fish caught suchi fast-movi „ fish, I am unable to. say. Common and lemon soles in the juvenile stages were .. both found in the skate, and sea horses and pipe fish were also preyed upon by therm p erc p,/ kahawai, and spined dogfish were fourid feeding on six species ot fish. All three preyed on sprats, while the spined dogfish was not averse from feeding on green-backed flounders and ' ‘ lemon soles in the juvenile stages. V The red gurnard, kingfish, and trumpeter each feed on five species of fish The kingfish and the gurnard both found „ne red cod appetising and all three led on ■nrafs An uncommon fish known as the rock cod and the well-known fktlicad both were found to feed on four species of fish, while the porbeagle shark, tone, ‘ - conger eel. and toad fish were found b.V the writer feeding on three species ot tish. • The sucker fish, horse mackerel, bass groper, warehon, green-back flounder. If biting, whiptail, elephant fish, thrasher

shark, and smooth-hound all feed on two species of fish. ■ The carpet shark, silversides, bastard red cod, common sole, lemon sole, yellow tail, snapper, stargazer, catfish, and taumaka each eat one species of fish. , "The teeth of the piscivorous (fisheaters) are usually strong, and may be acutely pointed, not only to catch, but also to tear their prey. The teeth on the sides of the lower jaw are strong and erect, being used to seize its victim; those on the roof qf the mouth are as a rule directed backwards towards the throat, and in some instances can be depressed to enable the fish to swallow its prey more easily, while at the same time they cannot be pressed forward, this effectively preventing any chance of the victim escaping.