Fish leaving home: How cichlids perfectly time independence

Shell-dwelling cichlids are known for their remarkable parental care, raising their young in abandoned snail shells. 

Researchers from the Max Planck Institute for Biological Intelligence have uncovered the intricate dynamics inside these shells using 3D-printed models. 

The findings reveal synchronized but independent routines between mothers and their larvae, offering valuable insights into the species’ brood care behaviors and innate biological processes.

Delicate balancing act of cichilds

For many species, deciding when offspring leave the safety of home is a delicate balancing act.

If the young depart too early, they risk being ill-equipped to survive; staying too long, however, can overstrain the parents’ resources. This pivotal moment can greatly impact the survival of both parents and offspring across the animal kingdom.

The team at Herwig Baier’s research department focused on Lamprologus ocellatus, a species of shell-dwelling cichlids found in Africa’s Lake Tanganyika. These fish exhibit highly social behavior and devoted parental care, which is uncommon among many fish species. 

Raising their offspring within abandoned snail shells adds an intriguing layer to their parenting, but until now, the activities within these homes remained largely a mystery.

Creative solution to study hidden behaviors

To investigate the hidden world inside the shells, lead researcher Ash Parker and her colleagues devised an ingenious method. They used 3D printers to create modified snail shells, designed to function as optimal homes for the fish while leaving one side open. 

When these shells were placed against the aquarium glass, researchers could capture videos and photos of the cichlids’ behaviors.

Using AI-assisted image analysis, the team identified fascinating behaviors unfolding in a precise sequence. 

After the mother lays the eggs in the upper chamber of the snail shell, the father fertilizes them. After two to three days, the larvae hatch and the mother carries them with her mouth to the lowest chamber of the shell.

Dedicated maternal care of cichlids 

Throughout the early days of the larvae’s development, the mother remains vigilant. She not only guards the shell but actively tends to the eggs and larvae by cleaning them with her mouth. 

Additionally, she uses rapid movements of her rear fins to ensure a steady flow of fresh water inside the shell, maintaining optimal conditions for her young.

By the seventh or eighth day, the larvae begin feeding independently and make tentative attempts at swimming. However, they remain in the darker, lower chambers of the shell until the ninth day, when their behavior undergoes a dramatic shift.

Cichlids ready to leave the shell

On the ninth day after fertilization, the larvae show a sudden preference for brighter areas. This intrinsic change in light sensitivity appears to signal their readiness to leave the shell for the first time.

The timing of their emergence, however, also relies on their mother’s brood-care efforts. 

When the researchers removed the mother from the setup, the larvae left the shell earlier, likely due to deteriorating water quality caused by the absence of her fin fanning.

Independent but synchronized schedules

Interestingly, the mother’s behavior follows a separate internal schedule. When presented with an older clutch of larvae that swam out earlier than she anticipated, she actively pushed them back into the shell, disregarding their advanced development.

These observations show that both the mother and the offspring follow independent, innate schedules that are nevertheless perfectly synchronized. Both mother and juveniles seem to instinctively align their routines, agreeing that the ninth day marks the ideal time for the young to leave the shell.

Implications for evolution and behavior

This study offers a rare glimpse into the intricate processes governing parental care in shell-dwelling cichlids. By identifying innate behavioral patterns and their coordination, the research lays the groundwork for exploring the evolutionary and neurological underpinnings of such complex behaviors.

The findings also highlight the role of environmental conditions, maternal intervention, and innate biological timing in ensuring the successful transition of offspring to independence. 

With 3D-printed technology and AI-driven analysis, the researchers have provided an unprecedented view into the hidden dynamics of these fascinating fish. 

Image Credit: MPI for Biological Intelligence/ Axel Griesch

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