Squid Loligo Gahi Research Articles

Biochemical genetic studies on the Patagonian squid Loligo gahi d'Orbigny. II. Population structure in Falkland waters using isozymes, morphometrics and life history data

Genetic population structure of the commercially fished Patagonian squid Loligo gahi d'Orbigny was examined by collecting 19 samples (1189 individuals) from Falkland waters between March 1987 and April 1988 and subjecting individuals to electrophoretic and morphometric analysis. Morphological features (dorsal mantle length, fin length oblique, fin width, interorbital width, tentacle length, length of arms I and II, and mid-mantle circumference), sex and stage of reproductive maturity (Lipinski's universal scale) were recorded prior to electrophoresis. Analyses of allele frequencies at six polymorphic loci provided no evidence of stock separation, and the frequency distribution of genotypic classes almost exclusively fitted Hardy-Weinberg expectations for a randomly interbreeding population. Nei's mean genetic distances and identities between samples ranged from 0.000–0.002 and 0.997–1.00, respectively, supporting the contention of a genetically homogeneous breeding unit. Multivariate analyses revealed significant differences in the morphometrics among certain samples collected at approximately the same time, especially of interorbital width, first arm length and fin width. This morphological differentiation was not correlated with differences at the genetic level. The frequency distribution of dorsal mantle length and stages of reproductive maturity through the year were compatible with two alternative interpretations of population structure: (i) the existence of two temporally distinct separate spawning populations, one autumn- and the other spring-spawning, or, (ii) that slow-growing or late spawned individuals spawn at 18 months old while most squid spawn at 1 yr old in the austral spring and summer. Although it is not possible to discount either interpretation unequivocally, the latter hypothesis of population structure is more congruent with existing genetic evidence.

Biochemical genetic studies on the Patagonian squid Loligo gahi d'Orbigny. I. Electrophoretic survey of genetic variability

19 samples (1189 individuals) of the commercially fished Patagonian squid Loligo gahi d'Orbigny were collected from Falkland waters between March 1987 and April 1988 and subjected to starch gel electrophoresis. 41 enzyme-coding loci were screened for polymorphism. Clearly resolved enzyme phenotypes were obtained at 21 loci of which six exhibited polymorphism (glutamate oxaloacetate transaminase, GOT-II, E.C. 2.6.1.1.; α-glycerophosphate dehydrogenase, α- GPDH, E.G. 1.1.1.8; isocitrate dehydrogenase, ICD, E.C. 1.1.1.42; malate dehydrogenase, MDH-II, E.G. 1.1.1.37; phosphogluconate dehydrogenase, PGD, E.C. 1.1.1.44; and phosphoglucose mutase, PGM, E.G. 2.7.5.1). Routine scoring at the 21 loci revealed moderate levels of genetic variability, with the proportion of polymorphic loci, P = 0.273, mean heterozygosities per locus = 0.0693, and the effective number of alleles, N e , with values of 1.13–1.83.