Sex identification of Albacore using a low cost genetic method

Sex identification of animal species is a critical piece of information to derive parameters for
population dynamic models. In the context of stock assessment (SA) for marine population, sex
identification provides information about the sex-ratio of the population which is subsequently used
to calculate the stock spawning biomass. In these SA models, sex-ratio can be set to a constant value
throughout the lives of individuals (e.g. 0.5) or age-structured to account for changes linked to the
physiology of individuals (e.g. females may live longer and represent a larger proportion of the
population) or the selectivity of the fishery (e.g. a gender may be more accessible to the fishery at
specific stages). The most common methods to identify sex are derived from direct observation of
gonads. However, scientists must access the whole fish, which is rarely the case for large pelagic
species in the IOTC fishery as fish that are landed have been gutted. Here we show the preliminary
results of sex identification of albacore (Thunnus alalunga) using a genetic method: Amplified
Fragment Length Polymorphism (AFLP). This polymerase chain reaction (PCR)-based genetic tool is a
highly sensitive method for detecting polymorphisms in DNA. We tested the hypothesis that male
and female albacore present a genetic polymorphism linked to sex. Using a multiplexing technique
(i.e. a combination of different restriction enzymes and PCR primers), we identified potential
locations in the albacore genome where polymorphism could occur. Comparing results between 3
males and 3 females of albacore, we were able to identify 1 marker over 64 combinations of primers
that led to potential sex-specific polymorphism identification. Higher sampling (40 males and 40
females) will be performed to confirm these results. This method has the advantage of being low
cost, simple to develop, requires few genetic laboratory analysis or preparation (DNA extraction, PCR,
electrophoresis and a capillary sequencer for DNA fragment analysis) and the genetic material
required is minimal and can be taken from a living or dead animal.