For aquarium hobbyists intentionally breeding fish species like guppies, mollies, and angelfish or accidentally encountering fry in community tanks, the sudden appearance of large numbers of tiny young fish swimming around can be a simultaneously exciting yet confusing experience.
While most juvenile fish are simply called “fry” in general terms, there are far more specific developmental stage names and terminology to describe baby fish depending on age and species. Understanding the nuances in the names for young fish stages helps provide proper care tailored to their needs at each vulnerable life phase. With appropriate conditions during their fragile early days, young fish can thrive into juveniles and adulthood.
Fish Reproductive Strategies
To understand the key differences in early development of baby fish, it is helpful to first briefly examine some common fish reproductive modes utilized by aquarium species:
Egg Layers
The vast majority of bony freshwater and saltwater fish species are oviparous egg layers, producing roe or eggs that are externally fertilized by male fish and deposited onto a spawning surface. The eggs then hatch later after a period of incubation.
Livebearers
Some popular freshwater fish groups like poeciliids – which include mollies, platies, guppies, and swordtails – are ovoviviparous livebearers. Their eggs initially hatch inside the female fish’s body, developing into free-swimming fry that are birthed fully formed.
Mouthbrooders
In some advanced cichlids species, the female fish takes fertilized eggs into her mouth after spawning to internally incubate and protect them for a period of days or weeks before finally releasing fully developed juvenile fish.
Names and Terms for Young Fish
Throughout development from hatching to adulthood, young fish pass through various early life stages with differing common names:
Fry
“Fry” is the term used to refer to recently hatched juvenile fish generally under one month old that are still developing independence and transitioning from nutritional reliance on yolk sacs to external live foods.
Fingerlings
Slightly older young fish that are becoming juveniles and reach around 1-3 months of age are frequently called “fingerlings” in reference to their small size at this stage, often just an inch or two long.
Parr
Specifically, young hatchlings of salmonid species including rainbow trout, steelhead, and salmon are termed “parr” in their first year to year and a half of life due to their distinct coated markings that serve as camouflage.
Smolt
When salmonid fry further mature and lose their parr marks around 12-18 months old in preparation for the physiological changes needed to transition from freshwater to saltwater, they are referred to as “smolt.”
Spat
A distinct term used for the planktonic larval stage of bivalve mollusks like oysters, clams, mussels, and scallops is “spat.” Once the microscopic larvae settle onto a surface following a floating dispersal phase and metamorphose into juveniles, they become known as spat.
Hatchling vs Larva vs Juvenile Stages
Upon initially emerging from eggs, newborn fish may be specifically called hatchlings. At the later larval stage still sustaining on yolk reserves, they transition into free-feeding and free-swimming juveniles as their adult body shape continues to develop and mature.
Typical Appearance of Newborn Fry
While appearance varies greatly between the thousands of fish species, some common characteristics of newly hatched fish include:
Diminutive Size
Most fish fry are extremely small at birth, often just a few millimeters in length in smaller species. Larger fish may be 1⁄4 inch in size. This tiny size makes them vulnerable to predators.
Subdued Coloration
Coloration is relatively subdued and transparent in many newborn fish fry, providing camouflage. Some livebearing species exhibit brighter hues. Horizontal striping for concealment is also common.
Distinctive Features
Large eyes; prominent yolk sacs; developing fins and organs; and egg teeth for hatching eggs are physical traits seen in the fry developmental stage.
High Activity Level
After an initial adjustment and absorption of yolk reserves, most fry quickly become actively swimming and hunting microscopic foods within a few days to a week after hatching or birth.
Caring for Fragile Juvenile Fish
Successfully raising delicate fry to adulthood requires attentive husbandry:
Tailored Housing Setups
Bare bottom tanks allow access to infusoria for first feeding fry. Plants offer shelter from aggression. Fine screens prevent dangerous jumping. Keep water pristine.
Age-Appropriate Feeding Strategies
At first, newly free-swimming fry need infusoria, then finely powdered preparations four to five times daily to locate food. As they grow, provide small live foods and crushed flake.
Monitoring Health and Development
Watch for any signs of deformities, disease, or problems with swim bladder inflation. Remove any dead or abnormal fry immediately to stop disease spread.
Transitioning to Main Display Tank
After 4-8 weeks of quarantined growth to double in size, juveniles can cautiously be moved to the main tank. Still observe for any aggression issues.
Species-Specific Fry Care Needs
Approaches may differ based on fish reproductive modes:
Livebearing Fry
Newborn livebearer fry can immediately accept fine powdered dry foods. House together densely for comfort.
Scattered Egg Layer Fry
Newly hatched tetra or barb fry need ample infusoria fed multiple times daily to locate nutrients. Egg scatterers are more delicate.
Mouthbrooder Fry
Avoid disturbing brooding cichlid parents until fry are independently released. Then provide small powdered foods frequently near shelter.
Guarded Egg Layer Fry
Species like angelfish care for free-swimming young. Monitor parental aggression. These fry may accept some powered food earlier than mouthbrooders.
Conclusion
While most young fish are commonly called “fry” in general, more specific developmental stage terms exist like fingerlings, parr, smolt, spat, and larvae. Providing tailored housing and nutrition suited to each species’ reproductive strategy and fry age allows even extremely fragile newborn fish to thrive into juveniles and adulthood to become vibrant aquarium additions. With attentive hatchery-like care, fishkeepers can successfully propagate many species.
What are the very smallest newborn baby fish called?
Fish immediately after hatching are referred to as either hatchlings or larvae. These developmental terms describe the earliest stages before transitioning into free-swimming fry.
At what age or size are juvenile fish considered mature juveniles?
As developing fry grow larger over the first several weeks to months and take on the defined body shape and finnage of mature adults, they graduate from the larval stage to become known as juveniles.
Do very young baby fish eat different foods than adult fish?
Yes, newly hatched fry first require microscopic live foods like infusoria. At around 1 month old, they transition to accept fine powdered dry diets formulated for juvenile fish growth needs.
What are signs that newly born fish fry are healthy?
Indicators of healthy fry are active hunting behaviors, full round bellies, clear eyes, intact fins, normal swimming, rapid growth, and lack of spots, lesions, or cottony growths requiring treatment.
At what size or age can juvenile fish safely be moved into a main display aquarium?
Small fry need 4-8 weeks in a protected nursery tank to grow large enough to avoid predation. Once juveniles have doubled in size, they can cautiously be introduced to the main tank community if aggression is monitored.
