Cory catfish are not nocturnal, unlike most catfish. Corydoras species are generally crepuscular, so they are most active during twilight. Corys prefer to swim and feed in the early evening and morning but also engage in limited activity interspersed with short resting periods during the daytime.
Knowing the daily rhythms of cory catfish is crucial for maintaining their physical and psychological health. Cory catfish are slightly different from other catfish species in this regard, so let us examine when corys are likely to be most and least active.
Cory Catfish Are Not Strictly Nocturnal
While catfish are usually active at night, most species of Corydoras are not nocturnal.
It is common to assume that corys are nocturnal because they are catfish, and their activity levels are usually lower during the day than the nighttime. This assumption is not entirely accurate because cory catfish also swim and feed during daylight hours, and rest intermittently during the day and night.
Instead of being nocturnal, most cory catfish species are crepuscular, so their activity levels peak in the twilight hours. These cory catfish remain active in the daytime, but they are more relaxed and subdued than during the early morning and evening hours.
There are exceptions to this rule. Certain corydoras species like albino corys are diurnal and prefer to eat during the daytime. On the other side of the spectrum are nocturnal cory catfish species such as panda and julii, which primarily rest during the day and are most active at night.
As a result of these differences, it is crucial to know which species of cory catfish you are caring for. This knowledge will enable you to provide appropriate conditions and feed them at the most advantageous time of the day.
When Do Cory Catfish Rest?
Fish do not sleep in the conventional sense because they do not have eyelids to shut, and their brains lack a neocortex (which plays a fundamental role during sleep). Instead, fish enter a resting state in which they become still and unresponsive for several minutes, allowing their bodies to recuperate as though they were sleeping.
Cory catfish do not have specific times when they prefer to rest. Instead, they take short naps throughout the day and night, resting whenever they perceive the need.
Despite this flexibility, cory catfish species usually spend more time resting during the day as opposed to the nighttime. Corys typically reduce their resting periods and become more active in the low-light levels of early morning and evening.
The small size and docile nature of corys mean they likely feel safer in the dark, which might contribute to increased activity in the evenings when other fish usually rest.
Ideal Feeding Time For Cory Catfish
The early evening is the best feeding time for most cory catfish species because the fish are starting to become more active. Feeding cory catfish at this time is also advantageous if larger and more aggressive fish are in the tank and might chase the corys away from their food.
This recommendation applies equally to crepuscular corydoras and the few nocturnal cory catfish species (such as julii and panda).
In the case of albino corys and other diurnal cory catfish, owners have more flexibility. Diurnal corydoras species are active in the bright daytime light, so it is okay for fish keepers to feed them in the morning, afternoon, or evening.
Do Cory Catfish Need Light At Night?
Cory catfish species do not require artificial lighting during the dark nighttime hours. This advice also applies to those species that are crepuscular and nocturnal.
Cory cats do not need light to illuminate their tanks because they use their barbels (the whisker-like protrusions on the sides of their mouths) to find food. The fish also use their neuromasts (sensitive nerves running along the length of their bodies) to sense and navigate their environments without their eyes.
In the wild, corys live in relatively murky water and spend most of their time in the lower levels of the water column. For this reason, cory catfish do not like bright light, even in the daytime, which means a light fixture shining into the tank at night will make the fish feel disturbed and unsettled.
Ensuring an ample supply of plant life in the aquarium is advisable so that corys have shaded, low-light places to retreat to in the daytime.
How Do You Tell If Cory Catfish Is Stressed?
Corys might feel stressed if the lighting in their tank is too bright or if they are fed at the wrong time and have their food stolen by large, aggressive diurnal fish species. But how do you tell if cory catfish are experiencing stress from their environment or living conditions?
There are numerous signs indicating that cory catfish are under stress and require intervention from their owners. If corys are consistently lethargic, including during the early morning and evening hours, there is a high probability the fish feel anxious or uncomfortable.
Sudden weight loss or disinterest in food is a classic signal that cory catfish are stressed. Another sign of stress is when cory catfish swim compulsively along the sides of the tank (a behavior called glass surfing).
You can also tell that cory catfish are under stress if they are constantly hiding away, breathing heavily, or showing a loss or darkening of color.
These stress signs can result from many factors, such as poor water conditions or having too few corys in the tank. The stress indicators might also be telling you that the tank is lit too brightly, has insufficient hiding places for corys to rest in the day, or that you are feeding the fish at an inopportune time
Conclusion
The majority of cory catfish species are crepuscular, not nocturnal. This means the fish are most active during the twilight hours in the early morning and evening. Caring for twilight-loving corys requires that the fish are fed in the early evening when they are more likely to access the food, and their larger tank-mates are resting
The corydoras genus is, however, large and diverse, so there is a small minority of cory catfish species that are nocturnal (julii and panda corys) or diurnal (albino cory cats). Unlike most corydoras species, these corys are least active in the twilight hours.