Are fish smarter than we thought? | DW Documentary

Key Concepts:

• Fish intelligence: Cognitive abilities, social organization, adaptability, and emotions in fish.
• Acoustic communication: Sound production and purpose in fish, including mating calls, territorial defense, and warning signals.
• Spatial memory: Fish's ability to memorize visual clues and navigate routes.
• Tool use: Fish species capable of using tools for feeding.
• Facial recognition: Fish's ability to recognize and discriminate human faces.
• Mirror self-recognition (MSR): The mark test and its application to fish, indicating self-awareness.
• Social behavior: Hierarchy in treatment of clients, cooperation, and strategic behavior in cleaner fish.
• Emotional contagion: Fish's ability to perceive and react to the pain of others.
• Emotional bonds: Pair bonding and the impact of separation on fish's emotional state.

1. Challenging the Myth of Fish Intelligence

• The common belief that goldfish have a 3-second memory is challenged.
• Researchers have conducted experiments to test fish intelligence, cognitive abilities, social organization, adaptability, and emotions.
• Japanese scientists demonstrated that goldfish could differentiate between Bach and Stravinsky by swimming to different corners of a tank for a food reward based on the music.

2. Acoustic Communication in Fish

• Fish communicate through sounds, despite lacking vocal cords.
• Bioacousticians Eric Pomier and David Leini use hydrophones to study the soundscape of coral reefs.
• Damsel fish produce "cooing" sounds by rapidly closing their mouths using a ligament connecting the tongue to the lower jaw.
• Soldier fish produce sounds by vibrating their swim bladder using muscles connected to the skull and ribs.
• Different fish species make different sounds, which can be used for identification.
• Fish communicate for mating, territorial defense, and warning signals.
• The sounds of a coral reef are an organized cacophony of communication.

3. Memory and Spatial Awareness

• Ethologists Kate Newport and Anna Garcia at the University of Oxford research the spatial memory of fish.
• Goldfish can memorize visual clues in their environment for orientation.
• Experiment: Goldfish were trained to swim a certain distance in a tank with black and white stripes. When the width of the stripes was doubled, the fish swam twice as far before turning around, indicating they were counting stripes to gauge distance.
• The misconception about fish memory stems from human bias, assuming fish are too different from humans to be intelligent.
• The location of memory processing in fish brains is not fully understood, but it may involve the hippocampus.

4. Training and Learning Abilities

• Fish can be trained with positive reinforcement, such as food rewards.
• Maurice the goldfish was trained to navigate obstacles in his aquarium for food.

5. Fish Evolution and Diversity

• Fish are vertebrates, just like humans.
• Science recognizes fish as a vast group of 33,000 species, almost 60% of all modern-day vertebrates.
• There are three classes of fish: bony fish, cartilaginous fish (sharks and rays), and jawless fish.
• From an evolutionary perspective, goldfish are closer to humans than sharks.
• 420 million years of fish evolution have allowed them to specialize and develop intelligence needed to survive underwater.

6. Tool Use in Fish

• The orange-dotted tusk fish uses its mouth to dig up clams and carries them to a rock (its anvil) to crack them open.
• Biologist Jacobo Bernardi documented this behavior, finding shell fragments at the "anvil" site.
• Documenting tool use in fish is challenging due to the limited time available for underwater research.

7. Facial Recognition in Archer Fish

• Archer fish can shoot down insects with a jet of water.
• Kate Newport's team discovered that archer fish can recognize human faces.
• Experiment: Archer fish were trained to spit at one of two faces for a reward. They could still recognize the trained face among 40 unfamiliar faces, even when the faces were rotated.
• Facial recognition in fish is remarkable, as even advanced computer programs struggle with this task.

8. Mirror Self-Recognition in Cleaner Wrasse

• The mirror self-recognition (MSR) test, or mark test, is used to determine if an animal recognizes itself in a mirror.
• Behavioral ecologist Alex Jordan tested the Pacific blue-striped cleaner wrasse, a fish that constantly removes parasites from itself and others.
• The cleaner wrasse initially showed aggressive behavior towards its reflection, then exhibited contingency testing behavior (swimming upside down).
• When a mark was applied to the fish, it attempted to remove it, indicating self-recognition.

9. Social Behavior and Strategic Interactions

• Leonor Boner researches cleaner wrasse in their natural habitat in Polynesia.
• Cleaner wrasse have cleaning stations where reef fish come to get rid of parasites.
• Cleaners treat clients differently based on a hierarchy: peaceful fish (visitors and residents) and predatory fish.
• Cleaners are more cooperative with predators to avoid becoming their meal.
• Cleaners sometimes "cheat" by eating the mucus layer of fish, but they may then provide a soothing massage to ensure the customer returns.
• The "audience effect" means cleaners are more cooperative with prestigious visitors, providing better service.
• Cleaners analyze their environment and adapt their behavior accordingly, only cheating when conditions are favorable.

10. Emotions in Fish

• Biologist Rui Olivera researches pain perception in fish.
• Fish have the cellular and molecular mechanisms to experience and avoid noxious stimuli.
• Experiment: Zebra fish were shown videos of other fish experiencing distress. The test fish imitated the distressed behavior and swam towards the distressed fish, indicating emotional contagion.
• This behavior suggests emotion recognition and may be an early sign of empathy.
• Salmon farms are now focusing on fish's emotional well-being, specifically depression.

11. Emotional Bonds in Cichlids

• Clou and Franak Savier Desom researched monogamous fish species, focusing on cichlids.
• Cichlids form committed partnerships, care for their young, and build nests.
• The ambiguity test was adapted from psychology to measure the emotional state of cichlids.
• Experiment: Female cichlids were exposed to boxes with black (reward), white (no reward), and gray (ambiguous) lids.
• Optimistic females opened the gray lid quickly. When separated from their partner, they became more pessimistic and opened the gray lid much later.
• This suggests an emotional bond between partners, which is adaptive because it ensures both parents care for their young, increasing reproductive success.

12. Conclusion

• Fish are capable of complex behaviors, intelligence, and emotions.
• Much remains to be discovered about fish, as over 90% of the oceans are unexplored.
• Fish are capable of much more than previously believed.