MERRINER: REPRODUCTIVE BIOLOGY OF THE WEAKFISH 



Scale samples were taken from under the tip of 

 the pectoral fin below the lateral line of 2,159 

 weakfish for age determination. Age-group or 

 age-class cited herein refers to the number of an- 

 nuli on scales. Weight in grams and length (total, 

 fork, and standard) in millimeters were recorded 

 from all specimens. 



Sex and maturation stage of gonads were as- 

 signed after macroscopic examination of the 

 gonads using a modification of the classification 

 of Kesteven (1960). Histological sections of repre- 

 sentative gonads in each stage provided verifica- 

 tion of maturation class assignment (Table 1). 



Gonad index indicated duration and peak of 

 spawning season as well as the age and size at 

 which weakfish attain sexual maturity. Gonads 

 from 571 females and 117 males from the Hat- 

 teras and Morehead City areas were preserved in 

 10% Formalin^ and used for analysis of gonad 

 condition. The index value equals the weight of 

 the preserved gonad, to the nearest 0.01 g, di- 

 vided by the body weight of the fish, to the 

 nearest 1.0 g, times 100. It represents the percent 

 contribution of gonads to total fish weight. 



Twenty-two female weakfish with well- 

 developed oocytes (mature ovaries) provided the 

 basis for fecundity relationships. Age-groups I 

 through IV are represented by 20 fish collected 

 between 25 May and 13 June 1969, from Pamlico 

 Sound. Age-group is represented by two females 

 collected near Morehead City on 4 June 1968. The 

 preserved ovaries were blotted dry and weighed 

 to the nearest 0.01 g. One ovary from each pair 

 was randomly selected for sampling. A thin slice 

 (1-2 mm) was cut from the anterior, middle, and 

 posterior regions of the ovary. These slices were 

 weighed to the nearest 0.0001 g and placed in 

 Gilson's solution for 8 to 12 h to facilitate egg 

 separation from connective tissue (Bagenal 

 1967). Then the sections were rinsed with tap 



"Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



water and teased apart with dissecting needles. 

 The separated egg samples were placed in a petri 

 dish which was areally divided as a 6 x 6 grid and 

 stirred until equally distributed within the dish 

 before counting. Specific grid sectors were ran- 

 domly selected. The portion of the sample counted 

 ranged from one-ninth in larger ovaries to a total 

 count in small ovaries. Counts were made using a 

 dissecting microscope and included all eggs hav- 

 ing yolk deposition equal to or greater than the 

 diameter of the oil globule. 



Treatment of fecundity data included analysis 

 of variance for age-groups through IV (Steel 

 and Torrie 1960) and linear regression. Fecundity 

 was related to total length (TL) and standard 

 length (SL) of the fish in millimeters using the 

 equation, 



F = aL^ 



where F = fecundity, 



L = total or standard length of the fish, 

 a, b = constants for the equation. 



Fecundity was related to fish weight in grams 

 using the equation, 



F = a +bW 



where F = fecundity, 

 W = fish weight, 

 a, b = constants for the equation. 



RESULTS 



Monthly summaries of testes maturation class- 

 es revealed an extended spawning season and an 

 early summer peak in spawning for male weak- 

 fish. Over one-fourth of the males sampled from 

 March through August were ripe running (Table 

 2) and over one-half were ripe running from April 

 through July. During September and October, 



Table l.— Gonad stage designations and macroscopic condition of the male drumming muscle used in describing 



weakfish maturity. 



Female 



Male 



Gonad stage' 



Gonad stage' 



Condition of drumming muscle 



Whiite, undeveloped 



Pink, beginning to ttiicken 



Red, ttiickened 



Deep red, very thick 



Red to deep red, thinner 



Mottled red to pale red, thinner 



Pink, thin 



Pink to white, thin 



'Roman numerals indicate the corresponding stage for the Kesteven scheme (1960). 



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