89. Franticly hovering Anthias

Subject:

Frantically hovering and dancing in the current, these Anthias (subfamily Anthiinae) form giant aggregations that feed on zooplankton.

These huge shoals are composed of many smaller groups known as harems. Each harem is led by a single dominant and colourful male. All anthias are born as females that can, when all factors are right, turn into males at a later stage of their lives.

Fish are the only vertebrates that change sex during their lifetime. The social structure of a harem is widespread amongst vertebrates; lions, baboons, elephant seals, and gorillas all live in harems, to name just a few.

Sex change in fish species is called sequential hermaphroditism. There are different types of sequential hermaphroditism; protogynous hermaphrodites, protandrous hermaphrodites, serial bidirectional hermaphrodites, and finally, synchronous hermaphrodites.

Protogynous hermaphroditism is when a female changes into a male. The name comes from “proto,” which means first, and “gyno,” which means female. This form is the most common.

Less common are the protandrous hermaphrodites. These fish start their lives as males and change at a later stage in life into females. Protandrous comes from the combination of “proto” (first) and “androus,” which means male. Clown or anemonefish belong to this group.

The third type of sequential hermaphroditism is the serial bidirectional hermaphrodites. Individuals in this group can change back and forth into the other sex. Usually, sequential hermaphrodites only change sex once in their lifetime, but the serial bidirectional hermaphrodites are able to do this several times depending on the situation the animal is facing. Most gobies belong to this group.

The last type is the group of synchronous hermaphrodites. This is the rarest group. Fish belonging to this group can be both female and male at the same time. Some gobies are synchronous hermaphrodites.

Let’s get into more detail regarding the protogynous hermaphrodites like these anthias. When the dominant male dies or disappears for whatever reason, it is usually the most dominant or largest female that now becomes the male. This sex change happens in different stages. First, the female that is destined to become male starts acting aggressively towards all other females. This is believed to prevent other females from going through this morphological change. Secondly, the now soon-to-be-male exhibits behaviour that one could expect from a dominant male, such as territorial defence. She takes an active role in defending the harem’s territory and protecting the harem members against other individuals not directly related to the group. This behavioural change can occur within several minutes to several hours after the disappearance of the socially dominant male. Later, over a period of several days to even weeks, the individual starts showing external and visual changes. It can be colour, size, and shape. Males are more colourful, bigger, and have a stronger build than females. The female has turned into a male and produces sperm. Now he can reproduce and father the next generation of anthias.

Technique:

When filming wide-angle scenes, it is important to fill a big area of the image with blue. The screen was, therefore, horizontally divided into approximately 2/3 of water and 1/3 of reef. This ratio often works best for underwater wide-angle scenes.

Filming location:

This short underwater videoclip has been filmed in the Maldives 🇲🇻

89. Franticly hovering Anthias

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