PDF Summary:What a Fish Knows, by Jonathan Balcombe

We often dismiss fish as unfeeling, robotic creatures with limited perception and awareness. But as Jonathan Balcombe reveals in What a Fish Knows, these remarkable creatures possess senses, emotions, and intelligence we're only beginning to fathom. Fish can hear ultralow and ultrahigh sounds, discern between familiar faces, engage in social relationships, and exhibit altruism and deception—traits once thought exclusive to humans and other mammals.

Balcombe dives into these revelatory findings, exploring fishes' advanced sensory capabilities, their complex mating and parenting systems, and examples of their learning and problem-solving abilities. In doing so, What a Fish Knows urges us to reassess what we think we know about the creatures inhabiting oceans, lakes, and rivers.

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• If you're a teacher or parent, you can design an educational activity for children that involves creating a comfortable environment for a classroom pet or plants. Have the children observe and record the pet's or plant's behavior and growth in response to various conditions, teaching them the importance of care and the impact of environment on living things.
• Start a journal to document instances where you witness animals seeking comfort or avoiding discomfort in nature documentaries or at zoos. Note the context and the behaviors exhibited. This practice can enhance your awareness of animal welfare and inform your choices, such as supporting wildlife conservation efforts or choosing products that are animal-friendly.
• You can enhance the well-being of your pet fish by consulting with a veterinarian about appropriate pain management. If you notice signs of distress or pain in your fish, such as changes in eating habits or unusual swimming patterns, seek professional advice on whether pain relief is necessary and how to administer it safely.

Fish Pursue Touch for Enjoyment and Relaxation

Balcombe describes the growing evidence that fishes experience pleasure just as other vertebrates do, and that this sensation is associated with a range of pleasurable states and emotions such as enjoying meals, recreation, comfort, and touch. He describes how surgeonfishes subjected to stressful situations were significantly more attracted to a mobile representation of a cleanerfish, and how their cortisol levels dropped when they could rub their bodies against the gently stroking model.

The author also shares numerous personal accounts of fishes who appear to show pleasurable responses to tactile stimulation by humans. For instance, one captive Midas cichlid repeatedly ascends to be lifted, stroked, and tossed back into his tank by a man. Balcombe connects these accounts to other behavioral observations of fishes rubbing and stroking each other in pleasurable contexts, such as when cleanerfishes caress their clients during grooming rituals. He explains how fish react with apparent happiness and relaxation to gentle stroking of their bodies, just as a human or a dog might respond to a massage.

Context

• The ability to experience pleasure likely has evolutionary benefits, such as reinforcing behaviors that are crucial for survival, like eating and social bonding.
• The attraction to cleanerfish models suggests an evolved behavior where fish seek out cleaning services as a coping mechanism to reduce stress and maintain health.
• In scientific studies, models or replicas of animals are often used to simulate interactions in a controlled environment. This allows researchers to observe behaviors without the variability introduced by using live animals.
• Providing enrichment activities, such as gentle handling or environmental stimulation, is important for the mental and physical health of captive fish, similar to practices used for other animals in zoos and aquariums.
• Physical contact, such as rubbing and stroking, can lead to the release of endorphins, which are chemicals in the brain that promote feelings of well-being and reduce stress.
• Studies have shown that the presence of cleanerfish can increase the diversity and abundance of fish species in coral reef environments, highlighting their ecological significance beyond individual interactions.
• Cortisol is a hormone associated with stress in many animals, including fish. Lower cortisol levels indicate reduced stress, suggesting that tactile interactions can have a calming effect.

Fishes Show Complex Social Behavior Indicating Emotional Awareness

Balcombe explores the evidence that supports fishes' capacity to experience a variety of emotional states. When subjected to frightening stimuli, they react in ways consistent with fear: fleeing, changing colors, releasing alarm chemicals, staying still (sometimes for minutes at a time), and avoiding the risky area for some time afterward. Research indicates that fishes brought up in confined environments without exposure to predators lose their ability to recognize them as a threat, which suggests that these responses are not merely “hardwired” instincts, but learned modifications that the individual develops through experience. Conversely, fishes given antianxiety drugs such as oxazepam spend less time cowering with their companions, venture farther afield from their shoalmates to examine their environment, and have improved abilities to locate food while in confined conditions.

When we observe fish pursuing each other, searching for food together, or migrating in massive coordinated schools, our common sense tells us that these are feeling individuals with emotional lives—a truth that modern ethology increasingly bears out.

Practical Tips

• Introduce controlled challenges into your routine to enhance your adaptability. Start with small, manageable changes, such as taking a different route to work or trying a new type of cuisine, and gradually increase the complexity of these challenges. This practice can help you become more comfortable with change and uncertainty, akin to how exposure to varied environments can help animals retain their survival instincts.
• You can observe your own responses to stress by keeping a stress diary for a week, noting situations that trigger anxiety and your reactions to them. By tracking your stressors and reactions, you can identify patterns and consider strategies to reduce anxiety, such as deep breathing exercises, mindfulness, or seeking professional advice if necessary.
• Create a simple board game that mimics fish social behaviors for educational purposes. Design game mechanics that require players to work together to find food, avoid predators, or migrate to a new location, reflecting the cooperative nature of fish. This can be a fun way to experience and appreciate the complexity of animal social interactions and apply the understanding of teamwork and strategy in a playful context.

Fishes Have Impressive Cognitive Abilities

Balcombe overturns the long-held belief that fishes have short and simple memories with a chapter titled "Brains Behind the Scales." The author argues that brain size and genetic similarity to humans are poor predictors of cognitive ability, and that a more relevant approach to exploring animals’ mental lives is to examine the cognitive demands of a species’ everyday existence. If a species must learn a complex set of rules to thrive and prosper, then the species has evolved the necessary mental tools to do so.

Fish Can Be Taught, Remember, and Solve Problems

Drawing on decades of scientific research about fish behavior, Balcombe reviews the astonishingly diverse range of behaviors that require intelligence, such as learning, memory, navigation, tool use, planning, and innovation.

To illustrate fishes' learning and memory abilities, Balcombe describes an experiment conducted in his laboratory. He placed a small hole in the middle of a vertical net that was pulled at regular intervals across an experimental tank holding a group of small, brightly colored rainbowfishes. After some initial panic, the rainbowfish quickly figured out how to escape through the hole as the net approached their end of the tank. Even more remarkable, when tested again a year later – after not having seen the net for eleven months – the fishes calmly swam through the escape hole, as if no time had passed since their training.

Balcombe explains the great variety of terms scientists use to describe learning phenomenon in fish. These include non-associative learning, transference of power, and repeated reversal acquisition. He explains how fishes learn through operant conditioning and describes an experiment from 1908 conducted by Jacob Reighard in which snappers were trained to avoid eating sardines dyed red, by the simple strategy of sewing stinging jellyfish tentacles into the red-dyed sardines’ mouths.

Context

• Fish have been shown to possess the ability to learn from their environment and retain information over long periods. This is similar to how mammals and birds learn and remember, indicating a level of cognitive complexity that challenges traditional views of fish as simple creatures.
• Rainbowfish are small, colorful freshwater fish native to Australia and New Guinea. They are known for their vibrant colors and are popular in aquariums.
• This type of learning involves a change in response to a stimulus after repeated exposure, without the need for a reward or punishment. It includes habituation, where an organism reduces its response to a repeated, harmless stimulus, and sensitization, where the response to a stimulus increases after exposure to a strong or noxious stimulus.
• In the context of the experiment, the snappers learned to associate the red color with a negative experience (the sting), which is a classic example of how animals can learn to avoid certain stimuli that predict unpleasant outcomes.

Fishes Recognize Individual Conspecifics and Form Long-Term Relationships

The author examines how fish recognize individuals and reveals their capacity to remember individuals from their own and other species, along with the nuances of their respective social roles, for weeks or months at a time. This allows individuals to form dominance hierarchies based on relative power and physical capabilities, to identify individuals who are more collaborative for future encounters, and even to develop personal bonds and companionships.

For instance, captive guppies quickly recognize other guppies in a socially simulated setting. They defer to larger, more dominant peers to escape being punished, while exploiting their own higher status than subordinates. The author shares the account of Rosamonde Cook, who befriended a small, young smallmouth bass kept in a tank near her college office. After feeding him for several weeks, the fish began to swim toward her whenever she walked past his tank, even if she was surrounded by a crowd of people, suggesting that he could identify her as a distinct individual.

Other Perspectives

• The methodology used to determine the duration of fish memory could affect the results; different experimental designs might yield different conclusions about the length of time fish can remember individuals.
• The formation of dominance hierarchies may vary greatly between species, and what is observed in one fish species may not be applicable to another, thus generalizing this behavior across all fish may be misleading.
• The term "quickly" is subjective and does not provide a clear timeframe for how fast recognition occurs, which could lead to misinterpretation of the guppies' actual recognition speed and efficiency.
• Deference to larger peers might not solely be to escape punishment; it could also be a strategy for resource allocation, mating opportunities, or maintaining social cohesion within the group.
• The term "exploit" implies a negative connotation, whereas in animal behavior, higher status individuals asserting their position could be a part of healthy social interaction that maintains group dynamics.
• The anecdotal evidence provided by Rosamonde Cook's experience with the smallmouth bass does not necessarily constitute scientific proof of individual recognition in fish, as it is a single observation and not a controlled experiment with replicable results.

Fishes Show Flexible Behaviors Like Using Tools and Pursuing Prey

Balcombe explores the evidence demonstrating that fishes can both plan future events and use tools—two skills long thought to be uniquely human. He explains how the orange-dotted tuskfish performs an elaborate series of actions, separated in time and space, to feed itself: digging up clams hidden in the sand using water jets created by snapping his gill covers, carrying the clam to a nearby rock, then smashing the clam against the rock to access the soft tissues inside. While skeptics might claim that this isn’t “true” tool use because the fish doesn’t actually wield a separate tool to manipulate the clam, Balcombe explains why fish, lacking grasping limbs and inhabiting a relatively dense medium such as water, can’t use tools in this way.

Tool use isn't confined to just a few fish types. For instance, the archerfish creates its own hunting projectile by squirting water from its mouth to knock insects off overhanging branches. Studies of captive archerfishes reveal that they can fine-tune their shooting skills by practicing, observing others, and accounting for the optical warping caused by aiming through the transition from water to air. The author also describes other instances of tool utilization, such as that involving captive cod who worked out how to use the plastic tags attached to their bodies by researchers to hook onto a food dispenser, thereby devising a more efficient way to nourish themselves than by grabbing the loop with their mouths.

Context

• Tool use in animals is often defined as the ability to use an object to achieve a goal, such as obtaining food. This behavior is observed in various species, including primates, birds, and some marine animals, indicating a level of problem-solving and cognitive ability.
• The archerfish's ability to squirt water involves precise control of mouth shape and pressure. They adjust the force and angle of the water jet to compensate for the refraction of light at the water-air interface, which distorts the apparent position of the prey.

Other Perspectives

• The examples provided may not represent a deliberate plan to use tools but rather a series of learned behaviors that lead to a desired outcome without the fish understanding the cause-and-effect relationship.
• The observation that archerfish can fine-tune their shooting skills in captivity might not necessarily translate to all individuals of the species, as there could be significant individual variation in learning and skill acquisition.
• The observed behavior of captive cod using plastic tags to hook onto a food dispenser might not necessarily indicate a deliberate or conscious use of tools, but could be a result of accidental or trial-and-error interactions with their environment.

Fishes' Social Structures and Dynamics Are Sophisticated

Balcombe further dismantles the “autopilot fish” stereotype with a chapter titled "A Fish's Acquaintances.” He explains that fish aren't solitary, indifferent automatons, but social creatures with vibrant, diverse social interactions ranging from temporary shoals to long-term relationships sustained by cooperation, compromise, and, in some cases, manipulation and deception.

Fish Form Social Hierarchies With Communication and Cooperation

In addition to recognizing one another as individuals, fishes communicate and work together. For instance, individuals may shoal with like-colored conspecifics to confuse their predators, or they may switch their preferred shoaling partner in the presence of an audience, selecting companions who are less efficient foragers or hiding their attraction to a particular female in hopes that a rival male will go for the less desirable one. In certain species, such as golden mbuna cichlids, males intervene to break up fights between females, and will even show favoritism toward unfamiliar females in hopes the female newcomer might become a future mate for him.

The author describes how fishes are adept at learning from one another, such as when young bats listen in to the echolocation calls of older, more experienced bats to find the best feeding locations, or when naive minnows become frightened of a predator after observing their more worldly colleagues' responses.

Context

• Individual recognition can provide survival advantages, such as identifying reliable partners for cooperative tasks like hunting or defense against predators.
• Fish release pheromones into the water to send messages about reproductive status or to signal distress, which can influence the behavior of other fish.
• Shoaling refers to fish swimming together for social reasons, while schooling involves synchronized swimming. Both behaviors can confuse predators and improve hydrodynamic efficiency.
• The term "conspecifics" refers to members of the same species. Shoaling with conspecifics can enhance social cohesion and communication within the group.
• In some cases, changing partners might be a strategy related to mate selection, where fish attempt to increase their attractiveness or desirability to potential mates.
• Choosing less efficient foragers could be a tactic to appear less competitive or threatening to potential mates, thereby increasing mating opportunities.
• Such behaviors may have evolved because they increase reproductive success. By being discreet, a male can potentially secure a mate without alerting competitors.
• In some species, males may intervene to ensure that conflicts do not disrupt access to resources such as food or territory, which can be crucial for the survival and reproductive success of the group.
• By favoring unfamiliar females, males might be seeking to introduce new genetic traits into their lineage, which can be beneficial in adapting to changing environmental conditions or resisting diseases.
• Bats often live in colonies, which can facilitate the transmission of knowledge and skills from experienced individuals to younger ones, enhancing survival and adaptation.
• Experienced individuals in a group play a crucial role in the survival of the group by acting as a source of information about potential threats.

Fish Learn From Others and Sense Fairness

Balcombe describes the mutualistic relationship between cleaner fish and clients as an example of a sophisticated social contract in fishes, one that bears a striking resemblance to businesses in human society. Cleanerfishes establish stations in reef environments, using bright colors and waving signals to attract "customers.” Fish looking to be cleaned come to these stations to have harmful organisms, decaying tissue, and unwanted markings removed from them. Clients benefit by receiving a spa treatment that helps prevent parasitism and infection, while cleaners are nourished. In some cases, clients queue up, waiting patiently for the services, with cleaning rates reaching up to 144 visits per day. Cleaners can discriminate between "regulars,” who live there and can visit again later, and “visitors,” who might travel to a different reef if they’re not cleaned promptly—a social distinction equivalent to Redouan Bshary's demonstration that cleaner wrasses learn to visit first the temporary red plate before the permanent blue plate.

Both clients and cleaners employ diverse deceptive tactics for personal gain. Cleaners may occasionally nibble on a client's mucus, which they prefer to parasites, causing the customer to “jolt” as an indication that they know they’ve been cheated. Clients who are prey to the cleaners (for example, groupers) can extend their jaws as an invitation to enter, but will sometimes snap their jaws shut when a cleaner ventures too far—a reminder to the cleaner to be more honest. In turn, client fish that aren't prey to the cleaners (for example, triggerfishes) will often chase after a cleaner who has cheated them, which makes the cleaners less likely to take bites in future interactions.

Context

• Cleaner fish, such as cleaner wrasses, play a crucial ecological role by maintaining the health of reef fish populations. They remove parasites, dead skin, and mucus, which can otherwise lead to infections and diseases.
• The high number of visits underscores the mutualistic relationship, where both parties benefit, highlighting the evolutionary advantages of cooperation in nature.
• The "jolt" reaction from the client fish is a behavioral response indicating discomfort or awareness of being cheated. This reaction can serve as a deterrent to the cleaner fish, discouraging them from repeating the behavior.

Other Perspectives

• The dynamics of the relationship can change based on external factors such as the presence of predators, environmental stressors, or changes in the abundance of parasites, which can alter the degree of mutualism.
• The effectiveness of bright colors and waving signals might vary depending on the visual capabilities of the client fish species and the environmental conditions, such as water clarity and light penetration.
• The focus on nourishment overlooks other potential costs or disadvantages for the cleaners, such as the opportunity cost of not engaging in other activities while waiting for or servicing clients.
• While cleaners may be able to distinguish between "regulars" and "visitors," it's possible that this behavior is not a conscious decision but rather a result of instinctual or conditioned responses to different patterns of interaction.
• The use of the term "remind" anthropomorphizes the fish, implying that they have a human-like understanding of honesty and dishonesty, which may not accurately reflect the cognitive processes of fish.
• The effectiveness of chasing as a deterrent may vary among different species of client fish, and some cleaners might not be as easily influenced by being chased.

Fish Transmit Migration Routes and Reproduction Sites

Balcombe examines how fish transmit cultural information across generations. He explains that, while genes direct instinctive behaviors, traditions such as migration routes and mating locations are learned from older, more experienced individuals.

Balcombe cites a twelve-year-long study on bluehead wrasses conducted by Robert Warner in the Panamanian San Blas Islands. Warner had noted that blueheads consistently returned to specific sites for daily matings, despite what seemed to humans like other equally suitable locations. When all resident blueheads were removed from a set of reefs and replaced with fishes taken from a different area, the newcomers didn’t go to the previously established mating sites, suggesting that these locations were not chosen based on some intrinsic quality, but based on social convention.

Context

• Similar cultural transmission is observed in other species, such as elephants, which pass down knowledge of water holes, and birds, which learn songs specific to their region from older birds.
• Instinctive behaviors provide an evolutionary advantage by ensuring that essential survival actions are performed correctly without the need for learning, which can be risky or time-consuming.
• Learning from experienced individuals can lead to more efficient foraging, safer migration routes, and successful reproduction strategies, enhancing the survival and reproductive success of the learners.
• Bluehead wrasses are small reef fish known for their complex social structures and behaviors, including distinct mating rituals and territoriality.
• Similar to human societies, where cultural norms and practices are passed down through generations, many animal species rely on social conventions to maintain group cohesion and ensure survival.

Reproductive Behaviors and Tactics of Fishes

Balcombe reveals the creative and groundbreaking ways that aquatic creatures reproduce, as well as strategies they employ to maximize their reproductive success in their diverse watery environments.

Fishes Exhibit Diverse Mating Systems and Reproductive Strategies

Balcombe examines the remarkable range of fish's sexual proclivities and challenges readers to expand their understanding of sex and gender beyond human social norms. He explains that fishes display the full gamut of sexual expression: most are gonochoristic, remaining male or female throughout life; but others regularly change sex according to the needs of the situation; and some can even fertilize themselves. Balcombe notes that fish have an unmatched degree of sexual adaptability compared to other vertebrates, quoting the ichthyologist Thavamani J. Pandian.

Fishes Often Shift Sex, Demonstrating Sexual Plasticity

Balcombe overturns the common misconception that every fish is sexually “boring.” He points out that, while most remain male or female throughout their lives, a surprising number are gender switchers, performing as males one year, as females the next, or changing sex as needed. This sort of sexual plasticity is especially common among reef fishes, and it occurs in more than 25% of the species there.

For instance, in clownfishes (the species featured in Finding Nemo), a breeding pair occupies the top spots in a social group, while several subordinate males patiently await their opportunity for advancement. If the female in the pair dies, her mate will switch genders and the next-in-line subordinate male will then become the new breeding male. (Balcombe points out that, in the movie, after Nemo’s mom was eaten, Marlin was supposed to turn female instead of only becoming a single parent.)

In creatures that dwell beyond the light's reaches, changing sex is less common, and many are simultaneous hermaphrodites, creating eggs and sperm simultaneously, rendering the challenging task of finding a mate in the vast, dark abyss irrelevant.

Context

• The process of changing sex involves complex hormonal changes that trigger the transformation of reproductive organs. This can include the restructuring of gonads and changes in secondary sexual characteristics.
• In reef environments, where space and resources can be limited, sexual plasticity allows fish to adapt to changing social hierarchies and optimize their reproductive output. This flexibility can be crucial for maintaining population stability and resilience.
• The social structure of clownfish is closely tied to their symbiotic relationship with sea anemones, which provide protection and a stable habitat.
• In the deep sea, resources are scarce, so simultaneous hermaphroditism allows organisms to conserve energy by not having to search extensively for a mate of the opposite sex.

Fish Use Courtship, Care for Offspring, and Tactics to Entice Partners and Progeny

Balcombe examines the diverse range of techniques that fishes use to attract prospective mates. This often involves visual cues and complex courtship dances, and sometimes, artistic expression. For instance, male pufferfishes carefully construct intricate patterns in the sand to entice females to lay their eggs there, decorating these with bits of crushed shells that may provide camouflage as well as help secure the eggs in place.

Similarly, many cichlids build elaborate structures made of sand and pebbles to attract mates. The author explains how females favor males that are stronger, healthier, and/or more resourceful, evaluating this through the quality and extravagance of their bower building efforts, thereby ensuring that their offspring have a father with “good genes.” Even among species that do not construct elaborate bowers, males still invest significant energy into readying the nesting area. For example, whitetail damselfish will spend hours cleaning the chosen rocky face, using their mouths (to pick up and blast sand), their bodies (to shield from intruding currents), and finally their mouths again, plucking off individual sand grains that remain attached.

Context

• The male pufferfish uses its fins to create these geometric designs, which can be up to 2 meters in diameter, over the course of several days.
• Similar behaviors are observed in other animal species, such as bowerbirds, which also build intricate structures to attract mates, highlighting a fascinating example of convergent evolution.
• This behavior reflects an adaptation to their specific environment, where clean, algae-free surfaces are crucial for egg adhesion and protection from predators.

Other Perspectives

• The focus on visual cues and complex dances may inadvertently downplay the role of female choice and the active role females play in mate selection, which can be based on a variety of factors beyond the male's visual displays.
• The use of crushed shells might not be solely for securing the eggs; it could also serve as a visual signal to the female pufferfish about the nesting site's location.
• The concept of "good genes" is complex and multifaceted, and what constitutes a good genetic match can vary widely even within a species, meaning that the correlation between bower building and genetic fitness is not always straightforward or universal.
• The emphasis on male investment in nesting areas might overshadow the contributions of females in other aspects of reproduction and care, such as egg production, brooding, and post-hatching care.

Fishes Use Innovative and Creative Reproductive Behaviors

Balcombe challenges readers to broaden their view of these creatures beyond that "primitive," reflexive, emotionless cliché. He achieves this by revealing the complexity and sophistication of fishes’ mating systems, illustrating the remarkable diversity of strategies they employ to optimize their prospects for reproductive success.

Fish Build Nests to Attract Partners and Guard Their Spawn

Balcombe reviews the variety of nesting strategies that fish employ to attract mates and to protect their offspring as they develop from egg to free-swimming juvenile. These range from elaborate sand structures to cavities dug beneath rocks and logs, from bubbles formed from modified saliva to the abdominal pouch of male seahorses, and even the skin of a parent catfish, who wears his clutch until the embryos develop and hatch.

In South America, banded acaras carefully choose a loose leaf to spawn on. The author notes that they test the suitability of potential leaves beforehand, practicing the motions of picking up and carrying the chosen leaf in their mouths, presumably in anticipation of having to move their eggs and juveniles post-spawning.

Context

• Fish inhabit a wide range of environments, from freshwater rivers and lakes to the vast ocean, which influences their nesting strategies. Different habitats provide unique challenges and resources that fish must adapt to when building nests.
• Male seahorses have a unique reproductive role where they carry the fertilized eggs in a specialized pouch. This adaptation allows for greater protection and control over the developmental environment of the offspring.
• By choosing specific leaves, banded acaras may also influence the local ecosystem, as their nesting sites can affect the distribution of plant material and the behavior of other aquatic organisms.

Fishes Use Deceptive Mating Behaviors Like Feigning Climaxes and Mimicry

Balcombe examines the manipulative tactics that aquatic vertebrates employ to maximize their reproductive potential, just as their land-dwelling vertebrate brethren do. For instance, female brown trouts will occasionally perform a fake orgasm without releasing their eggs, thereby duping a nearby male into ejaculating. This behavior is thought to be a way to test male viability or to attract more virile males.

The author explains that the colorful, circular anal fin spots on male cichlids of the Haplochromis group from Lake Malawi may not be egg mimicry, as has been commonly assumed. Rather, they act as a visual signal that excites females, thereby encouraging them to release sperm, which could more effectively fertilize eggs currently in their oral cavity.

In the armored catfishes of South America, copulation involves "sperm drinking," in which a female draws sperm from the male's vent, holds these in her digestive system, and deposits them onto her eggs held between her lower fins. Although we might reasonably expect that the sperm would be destroyed by the female’s digestive enzymes, adaptations such as rapid gut transit and breathing through the intestines have evolved to allow efficient delivery of undigested sperm to the eggs.

Context

• The process involves specialized adaptations in the female's digestive system to prevent the breakdown of sperm, which is unusual since digestive systems typically break down proteins and other biological materials.
• Some fish have developed the ability to absorb oxygen through their intestines, a process known as intestinal respiration. This adaptation can be crucial in low-oxygen environments and may also play a role in maintaining the viability of sperm during transit.

Other Perspectives

• The behavior of female brown trouts feigning climax could be interpreted differently; rather than being a deceptive tactic to test male viability or attract more virile males, it might be a mechanism to ensure genetic diversity by encouraging multiple matings.
• The causality between the presence of anal fin spots and female excitement could be questioned, as it might be that only certain females respond to these spots, or that the response is context-dependent rather than a universal reaction.

Fishes Demonstrate Remarkable Parental Care and Social Cooperation

Balcombe dispels the myth that fish are indifferent parents by revealing the extraordinary lengths that certain fish go to to care for their offspring. He explains that, while most fishes exhibit no parental care at all, approximately 25% of all fish species, and the majority of cichlids, provide some form of parental care for their eggs or young. He describes these diverse parenting strategies, showing that providing for one's young isn't restricted to mammals and birds.

Males Often Care for Eggs and Offspring

Balcombe describes the diverse strategies fish use to care for their young. This encompasses guarding, sheltering, and transporting, and sometimes even feeding their offspring. It’s not solely the mothers' duty. For instance, male cardinalfishes hold eggs inside their mouths and forgo eating during the weeks it takes for the embryos to hatch and develop. When danger approaches, the male wiggles his fins at the water's surface, signaling to the youngsters, who promptly return for safety in his mouth.

The prize for the most dedicated fathers must go to pipefishes and seahorses. In these closely related species, the males have an abdominal pouch in which they incubate the female’s eggs and care for the hatchlings until they emerge as miniature versions of their progenitors. Male pipefishes and seahorses undergo something like pregnancy, including labor contractions when they release their young—a system that ensures paternity assurance to the father and safety to the offspring.

Context

• The strategies employed by fish to care for their young directly impact the survival rates of the offspring. Effective parental care can lead to higher survival rates, which is crucial for species with high predation risks.
• By holding the young in their mouths, male cardinalfish can protect them from environmental hazards and predators, providing a mobile and secure environment until they are ready to survive independently.
• This form of male pregnancy is rare in the animal kingdom and is a distinctive feature of syngnathid fish, setting them apart from most other species where females typically carry the young.
• The process of releasing the young involves muscular contractions, akin to labor in mammals, which helps expel the fully developed offspring from the pouch into the water.

Other Perspectives

• The male's abdominal pouch provides physical protection, but it does not guarantee the offspring's safety from all threats, such as disease or genetic defects that may affect the young while they are still being incubated.

Even Nonparent Fish Cooperate to Protect and Care for Each Other's Young

Balcombe explains how the challenges of successful parenting have led certain fish species to develop cooperative breeding strategies, where nonbreeding individuals assist in raising the young of others. This is especially common among these innovative species: cichlids. Those helping at the nesting site take on various duties, such as defending the area, cleaning and fanning the eggs, and removing debris. The author describes an experiment conducted on daffodil cichlids, showing that individuals who are given the chance to form families of their own will abandon their roles as helpers to do so, backing the notion that helping behavior has evolved to optimize reproductive success in creatures where resources are scarce. The author likens these helping behaviors to "internships" or mentoring that may enhance parenting abilities in the future.

The author explores the darker side of cooperation by unveiling the brood parasitism practiced by cuckoo catfishes in Lake Tanganyika. Exploiting the parental attentiveness of mouthbrooding cichlids, cuckoo catfish females carefully place their own eggs among the host species’ clutch. The eggs of these catfish hatch first, and the young may then eat the cichlids’ babies. Despite being a sneaky, selfish tactic, Balcombe points out that, like many forms of cheating, this parasitic reproductive behavior is an effective strategy.

Balcombe concludes that fish are not simply things, but beings worthy of our moral consideration. He argues that intelligence and cognitive skill are ultimately irrelevant when it comes to considering them members of the moral circle. Sentience is foundational to ethics, and there is now overwhelming evidence that fishes feel and are aware. He references "the moral universe's arc," quoting Martin Luther King, Jr., to illuminate humanity's gradual progress toward expanding the moral circle to include all life. With the emergence of a more powerful and advanced animal rights movement, fueled by scientific breakthroughs and spurred by a mounting awareness of the interconnectedness of all life, he contends that humanity is at a "tipping point" in its relationship to animals. Balcombe’s work is both a testament to the progress already made and a hopeful vision for a future where fish are appreciated and respected for their intrinsic value beyond what they provide to humans.

Context

• Nonbreeding individuals may gain valuable parenting experience through cooperative breeding. This can enhance their future reproductive success when they eventually breed themselves, as they have already acquired skills in caring for young.
• For cuckoo catfish, this parasitic strategy is advantageous as it increases their reproductive success without the need for parental investment, allowing them to allocate energy to producing more offspring.

Other Perspectives

• The concept of "defending the area" can be complex, as territorial aggression among cichlids can sometimes lead to harm or stress for both the defenders and the intruders, which may not always be beneficial for the overall health of the group.
• The experiment on daffodil cichlids may not be generalizable to all fish species or even all cichlids, as different species can have varying social structures and breeding behaviors.
• Helping behavior could be driven by kin selection, where individuals help relatives raise offspring, thus indirectly passing on their genes, rather than directly optimizing their own reproductive success.
• Brood parasitism, while effective in the short term, may have negative impacts on the host species' population, potentially leading to a decline in the number of individuals available for future parasitism.
• Some argue that moral consideration should be proportionate to an animal's ability to experience suffering, and if fish have a less developed nervous system, they may not experience suffering in the same way as more complex animals.
• The concept of sentience as foundational to ethics is not universally accepted; some ethical theories prioritize other factors, such as ecological roles or the capacity for rational thought, over sentience.
• Practical considerations, such as the necessity of using animals for food, medical research, or other purposes, might limit the extent to which we can realistically expand our moral considerations.
• The concept of animal rights can vary greatly across different societies and cultures, which means that the movement's growth may not be uniform or universally accepted, potentially leading to conflicts and debates over the prioritization of human versus animal interests.
• While the notion of a tipping point suggests a significant shift in attitudes, it may be overly optimistic given the persistent challenges in changing deeply ingrained cultural practices and economic interests that do not prioritize animal welfare.