Dynamics of growth and development in tropical loliginid squid Photololigo species

Moltschaniwskyj, Natalie Ann (1994) Dynamics of growth and development in tropical loliginid squid Photololigo species. PhD thesis, James Cook University of North Queensland.

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Abstract

Temporal and spatial abundance of juveniles of two Photololigo species on the continental shelf off Townsville, Australia was described using light-traps. The two species showed very distinct and separate spatial distribution patterns. Photololigo sp. A was found close to the coast and was the smaller and more abundant of the two species. This species was most abundant in surface waters, although larger individuals were generally caught deeper. There was no evidence of vertical movements during the night. The presence of small and large juvenile Photololigo sp. A during summer and winter months suggests that spawning and recruitment occurs throughout the year. In contrast, Photololigo sp. B was caught predominantly offshore. All sizes of Photololigo sp. B were caught both close to the benthos and in surface waters in the middle of the Great Barrier Reef lagoon, but juveniles were deeper and larger further offshore. This study demonstrated that light-traps are an effective way of sampling and catching small loliginid squid for research.

This study approached growth of squid by examining the dynamics of muscle tissue and changes in shape and size of body structures in juvenile and adult Photololigo sp. A. Animals change shape during growth because body structures increase in size at different relative rates. These changes are of particular interest because they are generally concomitant with changes in ecology. Length and mass measurements were taken from squid ranging in size (dorsal mantle length) from 2.77 mm to 117.03 mm. Small squid (<50 mm dorsal mantle length) had round bodies with large head and eyes, and poorly developed tentacles and arms. Larger squid (> 50 mm dorsal mantle length) were more elongate and narrow and the head was proportionally smaller. As squid reached a dorsal mantle length of 60 mm, the changes in shape with growth become slower and they reached a final shape. Small individuals allocated energy predominantly in the arms and tentacles during early stages of growth, while the viscera and head grew at a much slower rate. Once individuals began producing gametic tissue and gonad growth occurred, the mantle muscle tissue grew more slowly than the gonad.

Allocation of energy to somatic and gametic growth was investigated using information about the way muscle tissue grows. Growth of somatic tissue in Photololigo sp. was expressed in terms of muscle fibre recruitment and growth. Muscle blocks and muscle fibres were measured and the size frequency distributions were compared between different size-classes of squid. Muscle blocks increased in size as individuals grew. The size frequency distribution of the muscle fibres suggested that this increase resulted from the generation of new muscle fibres and an increase in the size of existing muscle fibres. The size frequency distribution of muscle fibres was very similar in all size-classes of squid examined and the presence of small muscle fibres in all individuals suggested that muscle fibre recruitment may be continuous. Growth of muscle tissue, by muscle fibre growth and recruitment, provides a mechanism to explain the continuous growth described for tropical squid. Two structural types of muscle fibres; mitochondria-poor and mitochondria-rich, are present in juvenile and adult squid. A poor relationship between the ratio of the muscle fibre types and dorsal mantle length suggests that generation of mitochondria-rich muscle fibres may not be influenced by growth. The presence of what, histologically, appears to be a breakdown in the organisation of circular muscle fibres was dependent upon the size of the individual and its reproductive status. However, there was no evidence to suggest that this is part of the senescence process.

An influx of immature individuals was detected in early September and this group of individuals was followed throughout reproductive maturation. From the time female Photololigo began producing primary oocytes to ovulation was less than two months. Four pieces of evidence supported the hypothesis that Photololigo sp. A has the potential to lay multiple, discrete batches of eggs. (1) The ovaries of maturing and mature females contained a large population of primary oocytes. (2) There was a poor correlation between the size of females and both the oviduct mass and the number of eggs per mass of oviduct. (3) Rapid increase in the oviduct mass of mature females indicated that the ovary released batches of ovulated eggs. (4) Gonad mass increased at a relatively slow rate compared to the increase in somatic tissue. There was no evidence, from an examination of the length-weight relationships and microscopic assessment of the mantle muscle tissue, of a cost of egg production.

Item ID: 33786
Item Type: Thesis (PhD)
Keywords: squids; Photololigo; Cleveland Bay; distribution; growth; reproduction
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Publications arising from this thesis are available from the Related URLs field. The publications are:

Appendix 1: Moltschaniwskyj, N.A., and Doherty, P.J. (1995) Cross-shelf distribution patterns of tropical juvenile cephalopods sampled with light-traps. Marine and Freshwater Research, 46 (4). pp. 707-714.

Appendix 2: Moltschaniwskyj, N.A. (1994) Muscle tissue growth and muscle fibre dynamics in the tropical loliginid squid Photololigo sp. (Cephalopoda: Loliginidae). Canadian Journal of Fisheries and Aquatic Sciences, 51 (4). pp. 830-835.

Appendix 3: Moltschaniwskyj, Natalie A., and Doherty, Peter J. (1994) Distribution and abundance of two juvenile tropical Photololigo species (Cephalopoda: Loliginidae) in the central Great Barrier Reef Lagoon. Fishery Bulletin, 92 (2). pp. 302-312.

Date Deposited: 21 Jul 2015 04:53
FoR Codes: 06 BIOLOGICAL SCIENCES > 0602 Ecology > 060207 Population Ecology @ 50%
06 BIOLOGICAL SCIENCES > 0602 Ecology > 060205 Marine and Estuarine Ecology (incl Marine Ichthyology) @ 50%
SEO Codes: 96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960808 Marine Flora, Fauna and Biodiversity @ 100%
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