374 



Fishery Bulletin 93|2), 1995 



-„ Ritchie Bank ' 



North f »_ ORH 

 Island N u 



North Chatham Rise 

 ORH r— ^— -^ 



^ 



Chatham 

 Islands 



Figure 1 



Map of New Zealand and Exclusive Economic Zone and location of Chatham 

 Rise and Ritchie Bank orange roughy, Hoplostethus atlanticus, fisheries. 



development. Embryogenesis and larval development 

 of orange roughy are undescribed, as are the vertical 

 distributions of the eggs and larvae (Zeldis, 1993). 

 Orange roughy produce large eggs (2.32-mm mean 

 diameter) with a large oil droplet (0.60-mm mean di- 

 ameter), suggesting that their eggs would be strongly 

 positively buoyant (Robertson, 1981). Since egg devel- 

 opment rate in teleosts is strongly temperature depen- 

 dent (Pauly and Pullin, 1988; Pepin, 1991), changes 

 in the vertical distribution of orange roughy eggs dur- 

 ing embryogenesis will have a strong effect on their 

 development rate, because they are spawned in ther- 

 mally stratified waters below the mixed layer (Zeldis, 

 1993). Therefore, in order to estimate egg production 

 for orange roughy accurately, a model was needed which 

 considers the thermal history of an egg when the ob- 

 served stage of development is used to estimate age. 



To create and test this model, this study had the 

 following objectives: 1) to describe the temperature 

 dependence of egg development rate; 2) to estimate 

 ascent rates of egg stages with experimentation and 

 theory; 3) to combine results on development rate 

 and ascent rate to develop a 'thermal history model' 

 of orange roughy development in the water column; 

 and 4) to test predictions of this model against ob- 

 served vertical distributions of egg stages in the 

 water column. 



In this study a generalized description of embryol- 

 ogy is used to address these objectives. Photographs 

 of some of the egg and larval stages have been pub- 

 lished (Grimes and Zeldis, 1993), and detailed de- 

 scriptions of orange roughy embryological and lar- 

 val stages will be published separately. 



Methods 



Embryological, ascent rate and vertical distribution 

 studies were conducted on the North Chatham Rise 

 (Fig. 1) from 7 to 28 July 1992 with the MAF Fisher- 

 ies RV Tangaroa, a 70-m research stern trawler (voy- 

 age TAN9206). Additional embryological and ascent 

 rate studies were conducted on the Ritchie Bank from 

 6 June to 8 July 1993 during an egg production sur- 

 vey (Tangaroa voyage TAN9306). 



Embryology and development rates 



To study embryology and development rates, orange 

 roughy eggs were cultured under controlled-tempera- 

 ture conditions in a shipboard laboratory. The cul- 

 turing facility had four insulated, plastic 20-L bins, 

 in which plastic jars with mesh tops were submerged 

 to hold the eggs. Each bin had flow-through supplies 



