Determination of growth and related phenomena in Illex Illecebros Illecebrosus (LeSeur) (Decapoda: Cephalopoda) from Newfoundland

Lu, Chung-Cheng (1968) Determination of growth and related phenomena in Illex Illecebros Illecebrosus (LeSeur) (Decapoda: Cephalopoda) from Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

Sampling of the short-finned squid, Illex illecebrosus illecebrosus was undertaken during October and November, 1965; and July through October, 1966, at Holyrood, Conception Bay, Newfoundland. A total number of 1,262 squid was involved in the study of growth, sexual maturity, food, and various morphometrical indices associated with growth. From these squid, 400 mandibles were chosen to study with respect to the morphometry, pigmentation, and possible growth marks. -- Monthly samples show an increase in mantle length from July through October. A decrease in the mantle length occurs in the November samples, suggesting the appearance of a younger generation or second population. It is proposed that the spawning season for this species is from December through May of the following year. The spawning ground is postulated to be in the deeper water (i.e., 200 fathoms) of the various bays, or the deep water on the adjacent continental shelf. -- Analyses of the gastric and caecal contents indicate that fish is the main item in the diet. Cannibalism is found to be predominant in larger squid late in the inshore season. The wide variety of food items found in the alimentary canal, suggests that this squid demonstrates little selectivity in choice of prey. -- Morphometric indices HLI, HWI, MWI are found to decrease as the animal grows, indicating the growth of this animal is faster in length than in width. Index MEI also decreases as the animal grows, indicating the rapid development of the gonad and liver in this animal during its inshore migration. The decrease in MEI differs in rate with sex beyond a mantle length of 195 mm. in that the males mature earlier. The fin configuration is maintained unchanged throughout the size range studied, and therefore is identical in growth pattern to that described elsewhere for Lolliguncula brevis. -- The mandibles present an interesting field of future study. The growth of the mandible is isometric and detailed analysis indicates that a more valid relationship can be demonstrated between the size of the mandible and mantle length, than can be between mandible size and total body weight. The pigmentation of the wing of the lower mandible was studied by microprojection and microplanimeter and it is evident that a major change in the degree of pigmentation is correlated with an increase in mantle length, gonad weight and the advent of sexual maturity in both sexes. -- Microrings have been found on both the lateral wall of the lower mandible and as concentric lines in the otolith. Although the number of these mandibular microrings increases with size of the mandible, and therefore with age and maturity of the squid, no pattern or cyclic nature to their groupings could be distinguished at this time.

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