eCite Digital Repository

Gravid spot: a surrogate for predicting progress of embryonic development and reproductive output in a live bearing fish (Gambusia holbrooki)


Norazmi, L and Purser, J and Patil, J, Gravid spot: a surrogate for predicting progress of embryonic development and reproductive output in a live bearing fish (Gambusia holbrooki), Australian Society for Fish Biology - Oceania Chrondrichthyan Society Conference abstract book, 04-07 September 2016, Hobart, Tasmania (2016) [Conference Extract]

Pending copyright assessment - Request a copy


Brooding females of livebearing fish can be identified by the presence of the gravid spot; a dark pigmented spot located at a lateral and cranial position to the anal/genital pore. However, its use to predict embryonic development and clutch size remains unexplored. This study quantified visual attributes (intensity and size) of the gravid spot in relation to key features of internal embryonic development and clutch size in Gambusia holbrooki, a pest fish of concern to Australia. Observations show that the colour of the gravid spot arises from progressive melanisation on the surface of the ovarian sac. As predicted, the intensity and size of the gravid spot were closely linked with both developmental stage and clutch size, suggesting their reliable use as external surrogates. This reliability was harnessed to design and document downstream experiments on gestation, parturition and hormonal sex reversal. The gestation period was very sensitive to a small change in temperature—significantly longer (F=364.58; df=1,48; P<0.05) when reared at 23°C (897±43.93 degree days) compared to 25 °C (715±48.5 degree days). However, temperature did not have significant impact (P>0.05) on clutch size or diel timing of parturition which occurs predominantly in the morning (0900-1100h under 16:8h light: dark photoperiod, time on 0600h). The first-ever description on the birth posture of G. holbrooki fry (progenies) during parturition where the tail of the fry emerged first with a few exceptions of head-first, twin and premature births, was also documented. The reproducibility and utility of the relationships imply that they are also relevant to management of wild populations such as for stock assessment, monitoring environmental impacts, and control of pest populations among others. The observed embryonic superfetation and its relevance to reproductive adaptation and management will also be discussed.

Item Details

Item Type:Conference Extract
Keywords:Gambusia, gravid spot
Research Division:Agricultural, Veterinary and Food Sciences
Research Group:Fisheries sciences
Research Field:Fish pests and diseases
Objective Division:Environmental Management
Objective Group:Coastal and estuarine systems and management
Objective Field:Control of pests, diseases and exotic species in coastal and estuarine environments
UTAS Author:Norazmi, L (Dr Lokman Norazmi)
UTAS Author:Purser, J (Associate Professor John Purser)
UTAS Author:Patil, J (Dr Jawahar Patil)
ID Code:113208
Year Published:2016
Deposited By:Fisheries and Aquaculture
Deposited On:2016-12-15
Last Modified:2016-12-15

Repository Staff Only: item control page