Reproductive biology of the western king prawn Penaeus (Melicertus) latisulcatus (Kishinouye 1896) in Spencer Gulf and Gulf St Vincent, South Australia

Author: Nadine Hackett

Hackett, Nadine, 2017 Reproductive biology of the western king prawn Penaeus (Melicertus) latisulcatus (Kishinouye 1896) in Spencer Gulf and Gulf St Vincent, South Australia, Flinders University, School of Biological Sciences

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The western king prawn Penaeus (Melicertus) latisulcatus (Decapoda, Penaeidae) occurs within coastal waters of South Australia (Gulf St Vincent, Spencer Gulf and West Coast), but is also distributed in areas of northern and western Australia. There are considerable knowledge gaps in the fundamental reproductive biology of P. latisulcatus in southern Australia. The aim of this study was to examine the reproductive traits of P. latisulcatus by: i) improving the knowledge on the reproductive biology of western king prawns in South Australia and provide a better understanding for maturity indices and ovarian classification methods; and ii) identifying and assessing spawning occurrence in Spencer Gulf, South Australia.

Macroscopic staging is widely used in penaeid fisheries to identify ovarian stage. This research developed an improved microscopic assessment criterion for P. latisulcatus, by reviewing microscopic criteria in the literature, and assessing cell composition of ovary tissue from 97 females. The accuracy and precision of macroscopic staging was also determined. Macroscopic staging can be used as a rapid measure of spawning occurrence for penaeids; however, changes to the process of data collection should be incorporated into assessments to improve its accuracy.

Assessing the reproductive biology of penaeids is important in understanding the relationship between a species and its environment. The reproductive biology of P. latisulcatus in South Australia’s gulfs was described for females with a size range from 21 to 1 mm carapace length (CL), with the smallest ripe female sampled at 30 mm CL. Physical maturity of females was determined by the appearance, shape and colour of the thelycum. Gonadal somatic index (GSI) increased with CL and fecundity varied largely between individuals, ranging from 9,500 to 567,000 eggs counted per female. The thelycum of physically mature females were white and fully formed in shape while the thelycum of immature females were transparent and not fully formed. Size at 50 % physiological maturity was at 21.5 mm CL with the proportion of physically mature females increasing rapidly at larger sizes. A peak in the reproductive period in November was evident with a change in the number of females reaching reproductive maturity (increase from 9 to 27 %).

Detection of postovulatory follicles (POF) and their degeneration is commonly used to examine spawning incidence and batch fecundity in teleost species. Whilst efficient for fishes, this technique has never been applied to a penaeid prawn. POF were detected in histological examinations of P. latisulcatus ovaries and degeneration of POF was experimentally evaluated at 0 to 6, 12, 24, 48, 72 and 96 h post spawning. POF were then histologically classified which allowed clear detection of spawning events from 3 d post spawning. This experimentally derived classification can be used to improve the assessment of spawning incidences in prawns and the estimation of their spawning occurrence. Once histologically classified this assessment was used to identify the occurrence of POF in female P. latisulcatus and identify spawning occurrence among P. latisulcatus from females caught within a single spawning season in Spencer Gulf South Australia.

The findings presented here provide invaluable knowledge on the reproductive biology of female P. latisulcatus in southern Australia. The information can also be used for comparative studies with other penaeid species. The study demonstrates for the first time that POF can be used to detect spawning in a prawn species, which can lead to similar advancements in other prawns. This novel approach can thus improve the understanding of the reproductive biology of other commercially valuable prawn species.

Keywords: Prawn rerpoduction, P. latisulcatus, histological analysis

Subject: Biological Sciences thesis

Thesis type: Doctor of Philosophy
Completed: 2017
School: School of Biological Sciences
Supervisor: Sabine Dittmann