Unlike livestock, horses, and poultry, fish do not have a widely recognized sex-specific name that most people would know. A male cow is a bull, a male chicken is a rooster, but a male fish is, in most everyday situations, simply called a “male.” That said, specialized terms do exist in angling, aquaculture, and marine biology, and the vocabulary for describing male fish turns out to be surprisingly rich once you move past the generic label. The diversity of male forms in fish is so extreme that some males are parasites fused to a female’s body, some carry pregnancies, and some started life as females.
The General Term and the Angling Exceptions
In scientific literature, male fish are referred to as “males.” There is no Latin-derived or technical genus-wide word equivalent to “ram” or “stallion.” Biologists writing about any species, from guppies to groupers, consistently use “male” and “female” without further elaboration. This is partly because fish are so enormously diverse, spanning tens of thousands of species, that a single colloquial sex term never stuck.
The main exception comes from salmon and trout fishing, where anglers and fisheries managers have long used the term “cock fish” for a mature male and “hen fish” for a mature female. These terms persist in British, Irish, and Scandinavian angling traditions and still appear in fisheries reports and sport-fishing guides. You might also hear “milter” for a male fish that is ripe and releasing milt (sperm), and “spawner” for a female full of eggs, though “spawner” is sometimes applied to both sexes loosely. In aquaculture settings, broodstock managers refer to males and females plainly, sometimes specifying “broodstock males” when discussing fish kept specifically for breeding.
So if someone asks you “what is a male fish called,” the honest short answer is: just “male,” unless you are talking about salmon on a Scottish river, in which case “cock fish” is the traditional term.
Physical Features That Give Males Their Own Vocabulary
Where male fish terminology really expands is in describing the body parts and physical traits unique to males. Many of these structures are so distinctive that they have their own names, and understanding them is often more useful than knowing a generic label for the animal itself.
In salmon, mature males develop a pronounced hook on the tip of the lower jaw called a kype. The kype grows dramatically as the male prepares to spawn and is used in aggressive encounters with rival males on the spawning grounds. Studies of Atlantic salmon have examined the microstructure of kype skeletal tissues, documenting the rapid bone and cartilage growth involved in forming this hook.1The International Journal of Developmental Biology. Differentiation and growth of kype skeletal tissues in anadromous male Atlantic salmon (Salmo salar) After spawning, the kype is resorbed and the jaw gradually returns closer to its original shape, a process studied by comparing pre-spawned males (called grilse) with post-spawned males (called kelts).2PubMed Central. Seasonal changes in the lower jaw skeleton in male Atlantic salmon (Salmo salar L.): remodelling and regression of the kype after spawning These terms, grilse and kelt, technically describe life stages rather than sex, but because the kype is exclusive to males, the vocabulary around it is inherently tied to male fish.
In livebearing fish like guppies, swordtails, and mollies, the male’s anal fin is modified into a tube-like copulatory organ called a gonopodium. This is the easiest way to sex these fish in a home aquarium: if the anal fin is rod-shaped and pointed forward, you are looking at a male. Research on Trinidadian guppies has found that gonopodium length varies between populations depending on predation pressure, with juveniles in high-predation environments developing longer gonopodia, though that difference can disappear in adults because longer-gonopodia males face higher predation mortality.3PubMed Central. The complex ecology of genitalia: Gonopodium length and allometry in the Trinidadian guppy The shape and length of the gonopodium also predict mating success: variation in both measurements has been shown to affect the rate of genital contacts and insemination success during forced matings.4PubMed Central. Intraspecific evidence from guppies for correlated patterns of male and female genital trait diversification
In sharks, rays, and skates, male-specific structures called claspers serve as intromittent organs. Claspers are modifications of the pelvic fins and are visible externally, making sex identification straightforward in cartilaginous fish. Their internal anatomy includes specialized glands and skeletal elements that vary considerably between species.
Many freshwater species, particularly minnows and suckers, develop small raised bumps on their heads or fins during breeding season. These are called nuptial tubercles, sometimes nicknamed “breeding stars” or “pearl organs.” They appear almost exclusively on males and are thought to function in stimulating females during spawning and in male-to-male combat.
Sneakers, Satellites, and Pirates
One of the more fascinating aspects of male fish biology is that “male” does not always mean one thing, even within a single species. Many fish have evolved distinct male types that look different, behave differently, and reproduce using entirely different strategies. These alternative reproductive tactics come with their own labels.
Bluegill sunfish are a classic example. Males come in three forms: parentals, sneakers, and satellites. Parental males are the large, colorful individuals that build nests, court females, and guard eggs. Sneaker males are small and dart into a nest during spawning to release sperm before being chased away. Satellite males take a different approach entirely, mimicking the appearance and behavior of females to get close to a parental male’s nest without being attacked, then releasing sperm at the moment of spawning.5Behavioral Ecology and Sociobiology. Male size and mating tactic influence proximity to females during sperm competition in bluegill sunfish These are not temporary behaviors; parental males and sneaker males follow different developmental trajectories from a young age.
Cichlids show an even wider range. In at least one shell-brooding species, researchers have documented four distinct male tactics: pirates, territorials, satellites, and sneakers. A pirate temporarily displaces all other males from a shell nest, monopolizing spawning. Because sneakers always release their sperm in the presence of rival males, they face the highest levels of sperm competition, and their sperm has evolved to swim faster as a result. Pirate males, facing the least competition, have the slowest sperm.6Biology of Reproduction. Reproductive-Tactic-Specific Variation in Sperm Swimming Speeds in a Shell-Brooding Cichlid Similar patterns appear in other species: where sneaker males can’t compete through size or aggression, they compensate with superior sperm quality or quantity.7PubMed Central. Ejaculate Allocation and Sperm Characteristics Differ among Alternative Male Types in a Species of Fish with Cooperation and Competition among Unrelated Males
These alternative male types matter beyond academic curiosity. In conservation and fisheries management, assuming all males are interchangeable can lead to poor outcomes. Selectively removing the largest males through size-selective fishing, for instance, can shift the balance of mating tactics in a population and alter the dynamics of sexual selection in ways that affect population health.8PubMed Central. Implications of size-selective fisheries on sexual selection
When “Male” Is a Temporary State
In many reef fish, calling an individual a “male” describes its current condition rather than a permanent identity. Sequential hermaphroditism, where fish change sex during their lifetime, is common in coral reef species and adds another layer to the naming question.
Clownfish are protandrous hermaphrodites, meaning they start life as males and can become female. In a clownfish group living on an anemone, the largest individual is the breeding female, the second largest is the breeding male, and the rest are non-breeding males. If the female dies, the dominant male transforms into a female, and the next male in the hierarchy moves up to become the breeder. This process involves a complete restructuring of the gonads: as sex change progresses, testicular tissue steadily decreases while ovarian tissue increases, reaching about 87% ovarian tissue within 40 days of the triggering event.9Scientific Reports. Sex Change in Clownfish: Molecular Insights from Transcriptome Analysis – Section: Results
Interestingly, the behavioral shift does not keep pace with the physical one. Research on the common clownfish found that sex-changing fish displayed behavior that was persistently male-like even as their gonads were transforming, suggesting that behavioral sex change does not happen until after gonadal sex change is complete.10PubMed. Stable and persistent male-like behavior during male-to-female sex change in the common clownfish Amphiprion ocellaris So for a window of weeks, you can have a fish that is anatomically transitioning to female but still acting like a male. What do you call that individual? In the scientific literature, it is typically described as a “transitional” or “sex-changing” fish.
Wrasses and parrotfish go the other direction. They are protogynous, meaning they start as females and can become male. In many wrasse species, the largest, most colorful fish on the reef is a “terminal-phase male” or “supermale,” and it was born female. Research on the labrid family (wrasses and parrotfishes) has found that transitions trend toward monandry, a condition where all males in the population are derived from sex-changed females rather than being born male.11The American Naturalist. Correlated Evolution of Sex Allocation and Mating System in Wrasses and Parrotfishes In species where both born-males and sex-changed males coexist, they are sometimes distinguished as “primary males” and “secondary males,” respectively. Primary males often look like females and use sneaking tactics, while secondary males display bright coloration and defend territories.
Parasitic Males in the Deep Sea
The most extreme version of male specialization in fish belongs to certain deep-sea anglerfish. In several ceratioid anglerfish species, the male is a tiny creature, sometimes less than a tenth the size of the female, that bites onto her body and never lets go. Over time, the male’s tissues fuse with the female’s skin and their circulatory systems merge. The male loses his eyes, most of his internal organs, and his ability to feed independently. His single remaining function is to produce sperm, and he becomes entirely dependent on the female for blood-transported nutrients.12Nature. Precocious sexual parasitism in the deep sea ceratioid anglerfish, Cryptopsaras couesi Gill
The fusion is remarkably thorough. Histological studies have shown that in the fusion zone between the male’s head and the female’s skin, the dermis of both individuals merges completely, with no remnants of epidermis from either fish remaining.13Acta Zoologica. Histology of the fusion area between the parasitic male and the female in the deep‐sea anglerfish Neoceratias spinifer Pappenheim, 1914 (Teleostei, Ceratioidei) A single female can carry multiple parasitic males. These males are formally described as “parasitic males” in the literature, and the term fits: they are permanent sexual parasites, as dependent on their host as any tapeworm, just with the added twist that the host benefits from their presence.
Not all anglerfish species exhibit this extreme parasitism. In some, males attach temporarily during mating and then detach. The full parasitic fusion appears to be an adaptation to the vastly empty deep sea, where encounters between individuals are rare and holding onto a mate permanently offers a huge reproductive advantage.
Brood Males and Male Pregnancy
Seahorses, pipefishes, and sea dragons belong to the family Syngnathidae, and they are famous for a feature found nowhere else in the vertebrate world: male pregnancy. The female deposits her eggs into a specialized brood pouch on the male’s body, and the male carries the developing embryos, nourishing them through a placenta-like structure until they are born. Among different syngnathid species, there is a gradation of paternal involvement, from simple attachment of eggs to the male’s skin surface, through various degrees of skin-flap coverage, to full internal pregnancy within an enclosed brood pouch that resembles a mammalian uterus with a placenta.14PubMed Central. Seahorse Male Pregnancy as a Model System to Study Pregnancy, Immune Adaptations, and Environmental Effects
This arrangement creates genuine immunological challenges. The male’s immune system must tolerate genetically foreign embryos inside his body without rejecting them, a problem familiar from mammalian pregnancy research. Studies have found that seahorses have evolved specific adaptations in their toll-like receptor genes to manage this, facilitating paternal immune tolerance of the developing young.15PubMed Central. Gene loss and co-option of toll-like receptors facilitate paternal immunological adaptation in the brood pouch of pregnant male seahorses Hormonal regulation during male pregnancy also parallels some aspects of mammalian systems, with retinoic acid playing a regulatory role in the brood pouch.16PubMed Central. Regulatory Role of Retinoic Acid in Male Pregnancy of the Seahorse
In popular and scientific writing, pregnant male seahorses are often called “brood males” or simply “pregnant males.” The term is not metaphorical. They receive eggs, nourish embryos, regulate the internal environment, and give birth to live young. If any male fish deserves a special name beyond “male,” it is arguably these.
How a Fish Becomes Male in the First Place
In mammals, sex is almost always determined by chromosomes at fertilization. Fish are far less predictable. Some species have genetic sex determination systems resembling ours, others rely partly or entirely on environmental temperature during early development, and many fall somewhere in between.
The European sea bass illustrates this complexity well. Its sex ratios are influenced by both genetic factors and water temperature during early life. Key genes involved in sex differentiation, particularly cyp19a1a and dmrt1, show contrasting patterns of DNA methylation between males and females, and those patterns respond to temperature changes.17PubMed Central. Dynamic epimarks in sex-related genes predict gonad phenotype in the European sea bass, a fish with mixed genetic and environmental sex determination Exposure to high temperatures early in development can masculinize fish that would otherwise have developed as female, through a cascade of gene activation and epigenetic changes.18PubMed Central. Unraveling the genotype by environment interaction in a thermosensitive fish with a polygenic sex determination system
This means that in some fish species, whether an individual ends up being called a “male” at all depends on the water temperature it experienced as a larva. The boundary between male and female can be a sliding scale influenced by genetics, temperature, social cues, or some combination of all three.19PubMed Central. Temperature-dependent sex determination in fish revisited: prevalence, a single sex ratio response pattern, and possible effects of climate change Climate change, by shifting water temperatures, could alter the sex ratios of wild fish populations, potentially producing more males in species where heat promotes masculinization.
Hormones Behind Male Behavior
Once a fish does develop as male, the hormonal machinery driving its behavior is better understood in some species than others. The three-spined stickleback has been a workhorse for studying this. Male sticklebacks build elaborate nests, court females with a characteristic zigzag dance, and then guard the eggs, fanning them to ensure oxygen supply. Gonadectomy and hormone-replacement experiments have shown that male reproductive behaviors like territoriality, nest-building, and courtship are strongly driven by androgens, particularly a hormone called 11-ketotestosterone (11kT). During the breeding season, male sticklebacks have remarkably high plasma levels of 11kT, which also stimulates the development of secondary sexual characteristics including kidney hypertrophy and the production of a glue-like substance called spiggin that holds the nest together.20Behaviour. Hormonal Control of Male Reproductive Behaviour in Fishes: A Stickleback Perspective
There is a subtle but interesting wrinkle here. While androgens are critical for initiating breeding behavior, they seem to play a more permissive role once males are already established in a nesting cycle. And parental behaviors like egg-fanning appear to occur independently of androgen levels altogether. So the hormonal profile of a “male” stickleback shifts over the course of the breeding season in ways that decouple aggression and courtship from parental care. The fish that builds the nest and fights off rivals is hormonally different from the same fish a week later when it is patiently fanning eggs.
Why Fish Naming Is So Different from Other Animals
The reason fish lack the tidy sex-specific vocabulary we have for farm animals and game birds comes down to sheer diversity and the relatively late development of fish biology as a popular subject. Cattle, sheep, and horses have been domesticated for thousands of years, and the people who bred them needed quick, unambiguous terms to distinguish males from females at different life stages (colt versus filly, heifer versus bull calf). Fish, by contrast, were historically caught wild, eaten, and not individually managed. The exceptions, like salmon, are precisely the species where specialized terms did develop. Anglers who handled salmon individually on spawning rivers needed to distinguish sexes, and “cock” and “hen” filled that gap.
Modern aquaculture has not generated much new terminology either. Tilapia, catfish, and trout farms sex fish routinely, but the language stays clinical: male, female, broodstock male, neomale (a genetic female that has been sex-reversed to produce sperm). “Neomale” is about as exotic as aquaculture vocabulary gets, and it reflects the fact that sex manipulation in fish farming is a practical tool rather than a naming tradition. Nile tilapia farming, for example, often uses temperature or hormone treatment during early development to produce all-male populations, since males grow faster. The resulting fish are still just called males, even if their chromosomes say otherwise.