Male Vs. Female Bass

Bass can be difficult to sex alive.

The term “bass” refers to a number of different fresh and saltwater fish belonging to the Perciformes, or perch-like fishes. Freshwater bass are primarily native to North America, though one species, the Australian bass, lives in Australian rivers. Sea bass can be found throughout the world, from Chile to New Zealand. As with many other types of fish, it can be hard to tell male bass from females.

Breeding

It's easiest to distinguish male from female bass during the breeding season. During this period, mature females have visibly distended or sunken bellies, depending on whether they are ready to lay, or have recently laid their eggs. Most breeding females also have a small, red tube-like structure called an ovipositor extending from the opening on their undersides. Large bass without distended or sunken bellies are male, and very small bass are not yet sexually mature. Immature bass are difficult to distinguish without looking at their internal organs.

Internal Examination

Outside of the breeding season, sexing bass fish can be much more difficult. The most reliable method involves sacrificing the specimens to be sexed and examining their internal sex organs, or gonads. This technique provides a high rate of accuracy, and can even be used to determine the sex of immature fish. Unfortunately, it cannot be used in cases where the fish must be released alive afterward.

External Examination

According to Aquaculture Research, bass can also be sexed by looking at their urogenital openings and genital organs. This procedure is best done by trained personnel, since the visible differences are minor. For example, adult female rock bass have oval urogenital openings and blunt, red-tipped genital organs, while males have rounder openings and pointed, black-tipped organs. The two sexes may also have differently colored margins on the pelvic and anal fins. The genital organs themselves are very small, and difficult to examine on a live fish. Immature fish can be difficult to sex using this method.

Misconceptions

Several common methods of determining bass sex are actually ineffective. Outside the breeding season, females may have slightly more distended abdomens. However, fish which have recently eaten large prey show similar abdominal bulges. Changes in coloration associated with breeding are usually so short-term that they are not reliable. Squeezing fish to produce eggs or milt works only during the breeding season, and is often unreliable late or early in the season.

Expert Insight

According to Options Mediterraneennes, fish which are sexed for research purposes should be tagged before release. This prevents the need to re-determine the sex of the fish later. A PIT, or radio tag, is placed in the abdominal cavity or dorsal muscle. It does not affect growth or the health of the fish, and helps scientists determine the sex of the fish if it is caught again later.

References

• World Fishing Network: Determining Sex of Bass Fish
• Aquaculture Research: A method for sexing adult rock bass, ambloplites rupestris (Rafineque), in the field using external genital characteristics
• Options Mediterraneennes: Protocol M
• The Free Dictionary: Bass
• FishBase: List of Common Names for Bass