WHEN you're on the water with two or three anglers, some unusual topics can arise.

This was the case while I was fishing in Western Port with Brendan Wing and Gawaine Blake.

I was on their charter boat Think Big, hoping to hook a big gummy shark, and between changing baits and chasing big black stingrays the topic of sexing snapper arose.

Brendan holds a firm view on how to tell the difference between male and female snapper.

He said it was like telling the difference between a male and a female walking down the street: "You just know, by the build and the overall shape, which is which," he said.

Brendan believes the big snapper you catch, with the traditional lump on the forehead and the sharp taper to the tail, are the stallions of the breed: "Females have a heavier build and a more rounded head," he explained.

Marine biologists I have talked to say the only way to sex snapper is to examine their internal organs.

The problem is that most of the fish handled by scientists are small, and not the 7-10kg snapper that develop these distinctive shapes.

Another fishing writer, Geoff Wilson, supports Brendan's position and has for many years maintained that the big, hump-headed, snapper are males.

The surest way I know of telling the sex of snapper is that during the spring spawning run male snapper expel a milky fluid, called milt.

Female snapper, carrying roe or eggs, do not expel anything.

Sharks are the easiest creatures to sex, as the males have a pair of claspers.

These are rod-like extensions of the ventral fins, which run parallel with the shark's body towards the tail.

Then the subject turned to squid and how to tell the difference between sexes.

This was not a topic I had thought about. Squid were squid and I use them for bait, while most of my friends prefer them on the table.

I know squid can change colour fast and can disappear in a cloud of ink, which they use as a smoke screen. Squid are cephalopods, have three hearts pumping blue blood, are jet-powered and can swim forwards and backwards.

Cephalopods were once one of the dominant life forms in the world's ocean.

Today there are only about 800 living species of cephalopod, compared to more than 30,000 species of bony fish.

Due to overfishing of bony fishes, there may be a greater biomass of cephalopods in our oceans than ever before.

I started doing some research into squid and found that in early February, off the coast of southern California, squid up to 27kg and 1.2m long were being caught.

A report in the Los Angeles Times described the event as an invasion of giant squid in Orange County.

Colin Tannahill, from the Shimano Fishing Tackle company, was in the US recently and said anglers catching these huge squid were using "enormous squid jigs more than 30cm long and as thick as broomsticks".

On February 16, The New Zealand Herald ran a story under the headline: "Giant squid doesn't know how to use 2.5m sex organ".

This was an attention-grabber and opportune, given that it was sex (male or female gender, not the act) that I was interested in.

Never mind - the report raised several good points, including that in this case the female squid is a third larger than the male and the courting couple, both up to 18m long, each have eight legs and two tentacles.

The mind boggles.

But I'm navigating a different course.

The serious issue is how to sex squid, and if anyone knows this it will be the Japanese, as squid fishing is as much an institution as a recreation in the islands of the Rising Sun.

Colin emailed a Japanese contact, Masashi Arai, to ask him about squid genders.

He sent back pictures of each type, showing the male squid with distinctive "dot" markings and the female squid with "line" markings.

Mr Arai said: "This is quite famous information among Egi fisherman in Japan."

Brendan fished with some Japanese squid-jig manufacturers last year.

He knew from experience cleaning squid that the male tube was longer and the females had a shorter, broader tube.

On the fishing trip with the jig manufacturers he discovered that male squid have lines that flare out from the tube to the edge of the wings, while female squid show a pattern of dots running run down to their wings and across their backs.

Going over pictures of squid, I can see the colour differences for the first time.