641 



Spawning, growth, and overwintering size 

 of searobins (Triglidae: Prionotus carolinus 

 and P. evolansY 



Richard S. McBride 



Marine Field Station 



Institute of Manne and Coastal Sciences 



Rutgers University 



800 Great Bay Blvd 



Tuckerton, New Jersey 08087 



Present address: Florida Manne Research institute 

 100 Eigtith Avenue SE 

 St. Petersburg, Florida 33701-5095 



E-mail address rictiard mcbrideiff fwc state, fl us 



The northern searobin, Prionotus caro- 

 linus, and striped searobin. P. evolans, 

 are among the most common benthic 

 fishes of continental shelf waters 

 between Cape Cod and Cape Hatteras, 

 and both species have contributed 

 occasionally to landings of the U.S. 

 middle Atlantic states. Although sev- 

 eral life history studies of these species 

 have been published (Marshall, 1946; 

 Wong, 1968; McEachran and Davis, 

 1970; Richards et al., 1979; McBride 

 et al., 1998), their early life history 

 has been poorly documented until 

 recently (McBride and Able, 1994; Able 

 and Fahay 1998; McBride et al., 2002). 

 Obstacles to early life history studies 

 of these searobins include the follow- 

 ing: 1) eggs and preflexion larvae are 

 difficult to identify; 2) spawning occurs 

 concurrently for several months; 3) 

 slow growth rates confound analysis of 

 size frequencies for determining cohort 

 structure, and 4) conventional sam- 

 pling methods have provided few late- 

 stage larvae and early juveniles. I set 

 out to avoid these problems by collect- 

 ing juvenile specimens from the field 

 and analyzing their otolith microincre- 

 ments to determine spawning period- 

 icity and growth rates. This approach 

 has not previously been applied to any 

 triglidtSecoretal., 1992). 



This study demonstrates both inter- 

 specific and intraspecific differences in 

 size during the first year. A literature 

 review also suggests that age-0 P. caro- 

 linus are smaller than age-0 P. evolans 



and that conspecifics at northern 

 latitudes are larger than conspecif- 

 ics at southern latitudes (Table 1). In 

 this study, daily sagittal micro-incre- 

 ments were validated and used to test 

 whether interspecific spawning date 

 differences, growth rate differences, 

 or both, are responsible for size dif- 

 ferences at first winter. Size at first 

 annulus formation was also examined 

 as an independent measure of age and 

 growth rate. The results of this study 

 improve our understanding of the con- 

 tinental shelf as a nursery ground and 

 the geographic variation in life history 

 traits for these two species. 



Materials and methods 



Otolith micro-increment validation 



Otolith ontogeny was examined by 

 using cultured embryos and yolksac 

 larvae. Prionotus carolinus eggs were 

 collected from ripe adults in August 

 1992 in coastal waters and fertil- 

 ized in the laboratory. Embryos were 

 raised in 10-liter aquaria under a 12: 

 12 hour light:dark cycle, at 31 ppt 

 salinity, and 26°C. Cultured P. caroli- 

 nus embryos began to hatch after 48 

 hours and nearly all fish had hatched 

 by 56 hours. Laboratory temperatures 

 unintentionally dropped to 22°C after 

 hatching, but no mortality was ob- 

 served. Embryos and larvae were pre- 

 served in 95'7r ETOH at 8-16 hour 



intervals for the first three days and 

 22-26 hours for the following three 

 days. No fish survived beyond six days. 

 No water was exchanged, but constant 

 aeration kept the aquaria well mixed 

 during the experiment. Newly hatched 

 Artemia sp. nauplii were supplied to 

 yolksac larvae, but no feeding was 

 observed. All mortalities appeared to 

 be caused by starvation. 



Embryos or larvae were placed on a 

 slide under a cover slip or set in immer- 

 sion oil (Secor et al., 1992) to examine 

 otolith ontogeny. Otolith presence, size, 

 and development were noted with both a 

 binocular scope (<50x) and a compound 

 microscope (40-lOOOx) with polarized 

 light. Notochord length (NL) was mea- 

 sured with an ocular micrometer to the 

 nearest 0.1 mm. Otoliths were mea- 

 sured from a digitized video image 

 through a compound microscope to the 

 nearest 0.001 mm. 



Field-collected P. coro/inus juveniles 

 were chemically marked with tetra- 

 cycline, held in the laboratory under 

 controlled conditions, and the relation- 

 ship between "days captive" and "rings 

 after the tetracycline mark" was tested 

 against a 1:1 ratio. Newly settled P. 

 carolinus (10-15 mm standard length 

 |SL|) were collected near Beach Ha- 

 ven Ridge (New Jersey) by using a 

 1- or 2-m beam trawl on five different 

 dates in October 1992 (see McBride 

 et al. [2002] for sampling locations). 

 These fish were divided into four rep- 

 licate groups; each group was marked 

 separately with a solution of oxytet- 

 racycline (dihydrate) and ambient 

 seawater (a concentration of 500 mg/L; 

 26-28 ppt; 20-22°C) for 24 hours. 



One 40-liter aquarium per repli- 

 cate group was maintained as a flow- 

 through (about 1-10 mL/s) system. 

 Daily water temperature averaged 

 20.6°C (±2.7 SD), salinity averaged 

 28.5 ppt (±1.4) and the photoperiod 

 was 12:12 hours of light:dark. Tetra- 

 cycline-marked fish were fed thawed 

 Artemia sp. 2-4 times daily, and a sup- 



 Contribution 2002-15 of the Institute of 

 Marine and Coastal Sciences, Rutgers 

 University, New Brunswick, NJ 08901. 



Manuscript accepted 20 February 2002. 

 Fish. Bull. 100:641-647 (2002). 



