Johnson et al.: Evidence for distinct stocks of Scomberomorus cavalla 



95 



Results 



Of the 50 loci surveyed in 1985, 30% were variable. 

 In 1988, the 50 loci were again surveyed (879 fish 

 from 10 locations) and 24% of the loci were found 

 to have variants. Variations other than dipeptidase 

 (EN 3.4.-.-) PEPA-2 were found in low frequency 

 (uncommon allele 0.000 to 0.063) in 18 polymorphic 

 systems. Occurrence of these variants differed be- 

 tween locations and years. Electrophoretic variants 

 were found for loci including aspartate aminotrans- 

 ferase (EN 2.6.1.1) sAAT ", acid phosphatase (EN 

 3.1.3.2) ACP-2*, adenosine deaminase (EN 3.5.4.4) 

 ADA , adenylate kinase (EN 2.7.4.3) AK-1* and AK- 

 2' , alanine aminotransferase (EN 2.6.1.2) ALAT-1 

 and ALAT-2', esterase-D (EN 3.1.-.-) ESTD-2' and 

 ESTD-3 , fructose-bis-phosphate aldolase (EN 

 4.1.2.13) FBALD-2 \ glucose-6-phosphate isomerase 

 (EN 5.3.1.9) GPI-1* and GPI-2\ isocitrate dehydro- 

 genase (NADP + ) (EN 1.1.1.42) sIDHP , malic en- 

 zyme (NADP + ) (EN 1.1.1.38) ME-2' , mannose-6- 

 phosphate isomerase (EN 5.3.1.8) MPf, dipeptidase 

 (EN 3.4.-.-) PEPA-1 , phosphogluconate dehydroge- 

 nase (EN 1.1.1.44) PGDH*, and phosphoglucomutase 

 (EN5.4.2. 2) PGM-2*. 



Use of very low-frequency variations for stock 

 identification of king mackerel was impractical, be- 

 cause sufficient sample sizes (numbers of fish) for 

 detection during short time periods (one month or 

 less) were unavailable. Tagging studies (Fable et al., 

 1990 4 ) indicated that discrete geographic population 

 units were not available during the time intervals 

 required to obtain sufficient samples. Only dipepti- 

 dase (glycyl-leucine substrate) 5 consistently varied 

 between locations. In 1985 (1,223 fish), 1986 (1,537 

 fish), 1987 (2,120 fish), 1988 (1,631 fish), 1989(1,502 

 fish), and 1990 (963 fish), muscle tissues were ex- 

 amined for the dipeptidase variation. This enzyme 

 developed on electropherograms as two zones of 

 activity, and showed the pattern of a two allele ("a 

 and b) polymorphism in the most anodal zone 

 {PEPA-2\ in most collections, as described by May 

 [1983]). We refer to May's 1 and 2 alleles (electro- 

 morphs) as a and *b, respectively (Fig. 1). A third 

 allele (*c) which is anodal of the a allele was found 

 in 1988 and 1989 collections from Veracruz, Mexico 

 to Alabama. 6 Only one homozygote (*c*c) and 20 

 heterozygotes Cc'a) were found from 3,487 fish. 



5 Enzyme is also active with valyl-leucine and leucyl-tyrosine as 

 substrates. 



6 The genetic nomenclature for this polymorphic system accord- 

 ing to the recommendations of Shaklee, et al. (1990), is dipep- 

 tidase 3A.-APEPA-2') with three variant alleles '//(). '105, and 

 '100. These alleles are represented in this report as *c, *a, and 

 'b, respectively. 



PEPA-2 

 PEPA-1 



■Tit ••!••.— IV'Ii T 



(D 



'a'a a'b Vb 



(2) 



I 



 • 



^(3) 



Figure I 



King mackerel iScomberomorus cavalla) dipeptidase 

 (PEPA-P and PEPA-2*): (1) schematic of gel with 

 25 samples (PEPA-2* a is 0.700), (2) schematic of en- 

 largement of section of PEPA-2 on gel showing 

 three phenotypes ( a a, ab, b 6), and (3) photo- 

 graph of actual gel section used for schematic (2). 



Because of the rareness of this allele Cc), it was 

 combined with allele a for analysis. 



Allele frequencies and phenotypic distributions 

 varied extensively within and between areas from 

 1985 to 1990 (Table 1). The majority of monthly 

 collections conformed to the Hardy-Weinberg expec- 

 tation; however, many of the yearly collections did 

 not conform. In general, higher *a allele frequencies 

 were found west of Florida than in Florida and along 

 the Atlantic coast. 



The phenotypic distributions of the dipeptidase 

 polymorphism were not significantly correlated with 

 body length, with few exceptions. When the pheno- 

 typic distribution was compared by 100-mm-FL size 

 intervals for five geographic locations (Atlantic 

 coast, Alabama-Mississippi, Louisiana, east Texas, 

 and south Texas) by year, only seven of the 78 com- 

 parisons were significantly different (Kolmogorov- 

 Smirnov goodness-of-fit test, P<0.05). Four of these 



