Parrot Beak Syndrome Genetic Deformity in Trout
by Dick Marquand
This unusual brown trout was caught in Lake Dunstan by Trevor Phillips of Mosgiel. The brownie hen had a length of 44.5cm and a weight of 0.775kg, giving it a condition factor of about 32.
The “parrot beak” deformation has been caused by a genetic problem which goes back to cell division. when the embryo was developing inside the egg. I guess that we could compare this with the problem of a cleft palate in humans.
Some years ago, I caught a rainbow trout in Lake Dispute with the same deformity. That specimen was also a little down on condition.
Otago Fish and Game Officer Cliff Halford has been associated for many years with the Wanaka Trout Hatchery. On a number of occasions, he has seen young trout in the hatchery rearing tanks suffering from this problem. Any deformed trout developing in the hatchery complex is destroyed. In the wild, the vast majority of deformed trout, such as those suffering from “parrot beak syndrome,” fall prey to predators through a process known as natural selection. It is unusual for such a fish to grow to the size of the specimen caught by Trevor Phillips. Thanks, Trevor, for bringing this to our notice.
Mark Webb, Fish and Game Officer, Central South Island, Fish and Game Council, wrote the following in reply:
Parrot Beak Syndrome – Whale Nose (North of the Waitaki River) Your article by Dick Marquand regarding a deformed Lake Dunstan brown trout he had received from an angler. Mr Marquand’s conclusion based on the condition of this fish and others he caught some years ago, was that these ﬁsh are not able to compete with normal trout and are removed from the population by natural selection – survival of the fittest. This is an easily obtained conclusion given that the lack of a top jaw would in all likelihood create feeding problems for the affected trout. It is my experience that this conclusion may not be correct and that anglers may underestimate the durability and adaptability of trout.
From a total of 5792 rainbow trout trapped and tagged while on their spawning migration in Lake Alexandrina between 1986 and 1991 five “whale nose” trout were captured. There were 3 males and 2 females ranging in weight from 1330g to 2120g (average 1670g) and in length from 477mm to 533mm (average 503mm).
The condition factors of the whale nose trout ranged from 41 to 53 and averaged 47 compared to condition factors for the total 5792 rainbow trout which ranged from 26 to 66 and averaged 47. Although ﬁve fish is still a small sample on which to make conclusions it would appear that in Lake Alexandrina ‘whale nose’ fish do not exhibit any deviation from the norm as far as their condition is concerned.
Three of the deformed Alexandrina trout initially tagged prior to spawning were subsequently caught by anglers and tag information was returned to the Fish and Game Council. One fish was caught the season following tagging, one was caught two seasons after tagging – it was returned to the water by the first
angler. One angler noted that the fish “gave a hell of a fight” at it continually headed for the bottom of the lake and attempted to lose the line in the weed once there.
During Alexandrina trapping operations, 1241 brown trout were captured. None of these fish were observed with the top jaw deformity. The local variation in description of the deformity is also interesting. Does use of the word “parrot” infer all Otago trout are repetitions of each other and does the word “whale” suggest all Central Otago trout are big?