The use of multiple indices in the description of growth in the tropical estuarine fish Ambassis vachelli, Richardson (Pisces: Chandidae), with reference to the effects of feeding history

Molony, Brett Wymond (1993) The use of multiple indices in the description of growth in the tropical estuarine fish Ambassis vachelli, Richardson (Pisces: Chandidae), with reference to the effects of feeding history. PhD thesis, James Cook University.

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Ambassis vachelli (Richardson) was used as a model for a study of the growth of a short-lived fish species in tropical estuarine and coastal habitat. It was found that A. vachelli grows through four distinct stages of life based on biochemical, histological and otolith characteristics, living a maximum of one year. The different stages reflect the alteration of energy partitioning between somatic growth, storage and gonad development. It appears that the otoliths provide a permanent history of growth of the individual fish.

The populations of A. vachelli in the Townsville area vary in size and age structure. Estuarine tributaries are dominated by a single cohort that recruits early in the year. Shallow coastal areas are dominated by transient populations of large, old fish and may reflect the low cover in these waters. Although recruits are found in sheltered waters throughout the year the gonad data indicates that reproduction is concentrated in the wet season (November to March) and may be initiated by a reduction in salinity. It appears that fluctuations in temperatures (15 to 36°C) and salinities (0 to 36°‰) significantly influence the biochemical characteristics of juvenile fish. However, adult A. vachelli are able to tolerate a wide range of environmental conditions and differences in energy partitioning are likely to be due to maturation.

Pilot studies suggested that alterations to feeding regimes affected the growth and body constitution of A. vachelli. Two experiments were conducted examining the effects of feeding history on juveniles and adults. A. vachelli can sustain relatively long periods of starvation, although mortality increased rapidly in juveniles exposed to starvation. After a history of feeding juvenile fish displayed an increase in starvation resistance. Liver and viscera stores of lipid and carbohydrates are mobilised first during starvation, with carcass protein the least affected by prolonged starvation. Carcass protein sparing may be a strategy maintaining muscular integrity during period of low prey availability. Adults and juveniles recovered on feeding although the adults did not completely recover, and this may be due to differences in energy partitioning between juveniles and adults, with adults requiring energy for the development of the gonads. Overshoots, particularly in carbohydrate levels, were recorded on the resumption of feeding in all fish.

Otolith microstructure recorded changes in the growth of fish exposed to different feeding regimes, supporting the use of otolith microstructure as a record of daily fish growth. The rate of decline in increment widths in otoliths of starving fish was not altered by the feeding history of the individual. Liver somatic index and liver vacuole abundance also recorded changes in the abundance of stores in the fish with liver vacuole abundance being the most sensitive short-term index (days). The sagitta somatic index (SSI) was more sensitive to changes in body weight due to feeding regime than either the liver somatic index or Fulton's K. The sensitivity of the SSI as a condition index is due to the relatively small, stable weight of the sagitta as compared to fish weight.

The allocation of energy to the developing gonads allows the rapid development of the gonads. A. vachelli appears to be a multiple spawning species, producing several batches of eggs throughout the life of an individual, producing up to 3600 eggs throughout life. The biochemical development of the ovaries and testes varied and may reflect the function of each gamete.

The wide variety of indices and measures used in the present study provided a detailed insight of the growth of a small tropical fish inhabiting a widely variable environment. The indices applied to A. vachelli varied in regard to the time period over which each index and measure is most useful. The application of each technique should be based on these considerations.

Item ID: 27232
Item Type: Thesis (PhD)
Keywords: Ambassis vachelli; Townsville region; growth factors; growth stages; body constitution; energy partitioning; otolith microstructure; feeding history
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Appendix 10: Molony, B.W., and Choat, J.H. (1990) Otolith increment widths and somatic growth rate: the presence of a time-lag. Journal of Fish Biology, 37 (4). pp. 541-551.

Appendix 11: McCormick, M.I., and Molony, B.W. (1992) Effects of feeding history on the growth characteristics of a reef fish at settlement. Marine Biology, 114 (1). pp. 165-173.

Date Deposited: 25 Jun 2013 00:40
FoR Codes: 06 BIOLOGICAL SCIENCES > 0603 Evolutionary Biology > 060399 Evolutionary Biology not elsewhere classified @ 33%
06 BIOLOGICAL SCIENCES > 0608 Zoology > 060803 Animal Developmental and Reproductive Biology @ 34%
06 BIOLOGICAL SCIENCES > 0606 Physiology > 060699 Physiology not elsewhere classified @ 33%
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