HAYDOCK; GONAD MATLRATION OF GULF CROAKER 



Table 4. — GSI of Bairdiella leistia given six injections over a 15-day period (18-VIII-69 — 2-IX-69). Each in- 

 jection consisted of 1 mg salmon pituitary extract. Fish in groups 1 and 2 experienced a 16L:8D photoperiod; 

 groups 3 and 4 experienced 10L:14D for 2 months (to 28-VII-69) followed by day length increases to 16L:8D (by 

 22-VIII-69). Groups 1 and 3 were maintained at 22° C, groups 2 and 4 at 14° C throughout the experiments. 

 Symbols (S, E, +, — ) are the same as in Table 3. 



Table 5.— GSI of Bairdiella icistia given three injections, 

 one every other day for 7 days (16-IX— 23-IX-1969). 

 Photoperiod was 16L:8D and temperature 22° C during 

 this experiment. Symbols (S, E, +, — ) are the same 

 as in Table 3. 



en every other (3ay for 1 to 2 weeks (Table 3; 

 Table 4, groups 2 and 4). Fish in 22° C water 

 also showed a positive response (Table 4, groups 

 1 and 3; Table 5) ; however, this response is 

 less clear because warm-water fish occasionally 

 shed their eggs prior to sampling and this re- 

 duced the observed GSI. 



In general, fish with GSI values below 5 % 

 did not respond to the first injection ( — ), re- 

 sponded with a weak swelling in the genital area 

 ( + ) , or gave nonviable eggs ( E ) only after 

 several injections. This indicated that threshold 

 values of GSI and temperature exist below 

 which "growth" and above which hydration and 

 ovulation occur in response to hormone in- 

 jections. These values will be further discussed 

 in the section on ovulation. Here it will suffice 

 to point out that hormone treatment does give 

 rise to increases in gonad size which can perhaps 

 be considered the equivalent of gonad growth. 



The tabular data indicate that salmon pitui- 

 tary caused the greatest increase in GSI of fish 

 kept in cold water. Salmon was followed by 

 HCG and then DOC A (Table 3) . Salmon pitui- 



tary produced smaller increases in warm water 

 than in cold (Tables 3, 4, and 5), and the re- 

 sponse tended to vary in proportion to the dosage 

 used (Table 5). The relatively small response 

 at 22° C in Table 5 was probably due in part to 

 the lesser number of injections (3) in this batch 

 and in part to the fact that three of the fish 

 spawned relatively large quantities of eggs (see 

 qualitative responses in Table 5) , thus reducing 

 their GSI values, which were measured after 

 testing for the presence of viable eggs. How- 

 ever, the results of the longest series of injections 

 (Table 4) suggest that there is a general pat- 

 tern of greater increase in GSI in cold water, 

 except in the case of fish with a very low initial 

 GSI. 



In warm water (Table 4, group 1; Table 5), 

 fish produced viable eggs (S) or nonviable eggs 

 (E) which could be forced out the day after the 

 first injection. Cold-water fish (Table 3; Table 

 4, groups 2 and 4) required several injections 

 to produce a response and never spawned viable 

 eggs on stripping. 



In a further experiment, young-of-the-year 

 fish collected in October were injected shortly 

 thereafter with various concentrations of salmon 

 pituitary to assess usefulness of immatures as 

 a bioassay in testing dose-response relationships. 

 Each fish received five injections over a 10-day 

 period. At each dose level a large number of fish 

 (20) was injected, but, because of the difficulty 

 in identifying the sex of these immature fish, the 

 number of females actually injected was some- 

 what smaller. Also, the gonads were quite small, 

 and the overall GSI response was slight. This 

 made any meaningful analysis difficult. How- 



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