NOTES 



MARKING GROWTH INCREMENTS IN 



OTOLITHS OF LARVAL AND JUVENILE 



FISH BY IMMERSION IN TETRACYCLINE 



TO EXAMINE THE RATE OF 



INCREMENT FORMATION 



Age determination of fishes by counting daily growth 

 increments in their otoliths is becoming a widely used 

 technique in growth and population studies. Daily 

 formation of otolith increments was first reported by 

 Pannella (1971) for three species of temperate fish. 

 Since then a number of workers, using three basic 

 techniques for confirming the periodicity of incre- 

 ment formation, have reported the presence of daily 

 increments in larval or adult otoliths of at least 15 

 species of marine and freshwater fishes. Laboratory 

 rearing from eggs to larvae of known age was used to 

 confirm daily increments by brothers et al. (1976), 

 Taubert and Coble (1977), Barkman (1978), Tanaka 

 etal. (1981), and Laroche et al. (1982). The change in 

 the mean number of increments over time in fish cap- 

 tured in the wild and held in captivity was used to 

 validate daily increments by Struhsaker and 

 Uchiyama (1976), Wilson and Larkin (1980), and 

 Uchiyama and Struhsaker (1981). The third method 

 makes use of chemical agents to mark the growing 

 margin of calcified structures in order to examine their 

 rate of growth (Harris 1960). Tetracycline is one of 

 the best chemical markers because it is relatively 

 nontoxic and produces a fluorescent mark which is 

 easily viewed in ultraviolet light (Harris 1 960; Weber 

 and Ridgway 1962). It has been administered to fish 

 by feeding (Choate 1964; Weber and Ridgway 1967; 

 Trojnar 1973; Odense and Logan 1974) and by injec- 

 tion (Kobayashi et al. 1964 and others below). Tet- 

 racycline has been used in two studies to determine 

 the rate of increment formation in otoliths. Wild and 

 Foreman (1980) injected the drug into large juveniles 

 and adult skipjack tuna, Kotsuwonus pelamis, and 

 yellowfin tuna, Thunnus albacares, in a mark- 

 recapture program in the tropical eastern Pacific. 

 They found that otoliths of yellowfin tuna of 40-110 

 cm FL showed daily average increment formation, 

 but that skipjack tuna of 42-64 cm FL showed <1 

 increment/d. Campana and Neilson (1982) injected 

 tetracycline into juvenile starry flounders, Platich- 

 thys stellatus, and found that daily increments were 

 subsequently produced in both field and laboratory 

 conditions. These authors briefly mentioned obtain- 

 ing similar marking results by immersion, but did not 

 detail their procedure. 



This paper presents a technique for marking otolith 

 increments by immersing larval and juvenile fish in a 

 solution of tetracycline in seawater, and reports the 

 rate of increment formation under laboratory con- 

 ditions for two species from the Great Barrier Reef, 

 Australia: Hypoatherina tropicalis (Altherinidae) and 

 Spratelloides dellicatulus (Dussumeriidae). 



Materials and Methods 



The experiments were conducted between July 

 1980 and February 1982 at One Tree Island Field 

 Station and Lizard Island Research Station, during a 

 field study of the population dynamics of these 

 species. 



Achromycin (a brand of tetracycline HC1 1 ) was used 

 in all experiments. The concentration that would 

 mark the otoliths but not kill the fish was determined 

 by testing three concentrations (400 mg/1, 250 mg/1, 

 and 40 mg/1) using//, tropicalis from 12.8 to 23.0 mm 

 SL. The otoliths of survivors were compared with 

 untreated specimens to assess the effectiveness of 

 the mark. 



The appropriate concentration, 250 mg/1, was then 

 used in a series of similar experiments to determine 

 the rate of increment formation (Table 1). The 

 experiment number (I-IV) designates a group offish 

 collected at the same time. In each experiment, fish 

 were killed at two different times, designated as A or 

 B, to compare the number of increments in fish held 

 for different time periods. In experiment IV, the 

 treatment times also differed, but in all other 

 experiments the treatment time was the same for 

 both groups A and B. 



Both species are small (adults <7 cm SL), mid- 

 water, reef-associated, schooling fishes which do not 

 undergo a marked metamorphosis between larval 

 and juvenile stages (pers. observ.). Both attain their 

 full complement of fin elements and begin to form 

 scales and adult pigmentation at a standard length of 

 17-19 mm. Following the convention of Ahlstrom 

 (1968), I consider this to be the size at which larvae 

 become juveniles. Hypoatherina tropicalis used in the 

 rate-determination experiments ranged from 12.8 to 

 27.2 mm SL, with 10 of 21 fish classed as larvae 

 (<17.0 mm SL). Spratelloides delicatulus ranged 

 from 15.5 to 22.9 mm SL, with 2 of 29 being larvae 

 (Table 1). 



'Manufactured by Lederle Labs, a division of Cyanamid Australia 

 Pty. Ltd. References to trade names do not imply endorsement by 

 the National Marine Fisheries Service, NOAA. 



FISHERY Bl'LLKTIN: VOL. 82, NO. 1, 1984. 



237 



