Feeding Larvae / Fry After Dark

Does anyone feed small fish when lights are down / at low levels. Especially folks that rear relatively large numbers in tanks / aquaria. Sometimes we do, sometimes not. For some types of fish I rear it can make a huge difference although with others no benefits are evident.

My adult livebearers (guppies, heterandria formosa) are worse at hunting fry in dim light. But I find that as long as I feed the adults enough live worms, they don't attempt to eat the fry. So I keep the lights at normal levels. This helps the fry hunt for food.

James, what do you mean by "difference"? Do they eat more food in dim light? Or grow more evenly? Consume new foods that they would not eat under brighter light? What kinds of fish show this response to dim light?

Does anyone feed small fish when lights are down / at low levels. Especially folks that rear relatively large numbers in tanks / aquaria. Sometimes we do, sometimes not. For some types of fish I rear it can make a huge difference although with others no benefits are evident.

In past we restricted feedings of larval fishes (sunfishes mostly) to between 0800 and 1700 with intervals of about 2 hours. Growth rates were inferior to pond setting. I began playing around with collecting larvae from ponds at night and evidence suggested feeding was not restricted to corresponding times fish were fed in lab and even indicated feeding occured after dark. So we started feeding at 2-hour intervals around clock and started getting awsome growth like in a well managed pond. Labor inputs were not cost effective so we backed off on intervals but made so forage was availble at all times, even when lighting simulated darkness. Darkness in pond or how we rear now is not really the absence of light like many indoor rearing efforts are capable of realizing.

I was wondering if others explored applying feeds during night with other species, in addition to daytime feedings.

In past we restricted feedings of larval fishes (sunfishes mostly) to between 0800 and 1700 with intervals of about 2 hours. Growth rates were inferior to pond setting. I began playing around with collecting larvae from ponds at night and evidence suggested feeding was not restricted to corresponding times fish were fed in lab and even indicated feeding occured after dark. So we started feeding at 2-hour intervals around clock and started getting awsome growth like in a well managed pond. Labor inputs were not cost effective so we backed off on intervals but made so forage was availble at all times, even when lighting simulated darkness. Darkness in pond or how we rear now is not really the absence of light like many indoor rearing efforts are capable of realizing.

I was wondering if others explored applying feeds during night with other species, in addition to daytime feedings.

oh, that's what you're talking about. Yes, I specifically use a food that stays alive after adding it to the tank on purpose because I find that fry that can forage for food at any time grow faster than fry fed at only specific times. Microworms stay alive and wiggling in fresh or saltwater for two or three days. I add them to the tank once a day. Whenever I stop adding microworms to the tank and feed only crushed flake (for example this week, as I am harvesting from my microworms solely to make seed cultures to sell at a convention on Saturday), the stomachs of the fry are less full. You can see the difference just by looking at them. Although I should note that there is a certain level of baseline foraging in any well established tank. When I left for a week for Christmas and came back and turned the lights on again, the fry had grown even with no feeding of the tank whatsoever. The microworms would have only lasted a few days. I've got to imagine they're foraging on rotting flakes or tiny bugs or something. But yeah, baby fish grow fastest when food is constantly available, not batch fed. *nods* I agree.

Edited by EricaWieser, 16 January 2013 - 09:01 PM.

Have you ever tried feeding in the dark only?

We are going to try that soon. Problem has been defining dark. Larvae will be housed in buckets with lights in them and covered with a tight lid. Some will get light as we have provided in past (16 L: 14 D), some continous light (24 L: 0 D), and some no light (0 L: 24 D) with a couple of other intermediate treatments. We had to change bucket / lid material to limit transmission of light from outside into bucket but still not 100% controlled. Also lights heat water so challenge has been to keep all treatments the same temperature. If we are not careful temperature will vary with lighting regimen and temperature does have an non-quantified impact.

I am not sure if this is a factor, but it is food for thought. One of my favorite pastimes is to go out to my pond after dark with a flashlight, and watch the nightly midge hatch. It is really fun to watch them wriggle to the surface, and in a split second, fly away. I imagine juvenile fish take advantage of this opportunity, and gorge themselves. Maybe they are programmed to feed after dark due to the midge hatch, the lack of overhead predators, and the general cloak of darkness. It seems that adult sunfish feeding drops off sharply after dark, from an angling perspective, and also if I feed my pond a bit too late in the evening.

The heat problem could be solved with a segregated raceway, so that the same water flowed through all treatments but the fish were separated by screens.

We are doing similar to that already with buckets plumbed in parallel withing same system. Even with such arrangement heat from light sources sufficient to heat water enough to detect. Problem would be reduced if LED's used but cost is at present prohibative.


I want to upload image but cannot figure how to do it.

Your problem may be convective heat from the bulb, then, and not just radiant heat from absorbed light. Perhaps the light could be positioned further away?

That could be done although we will have to figure how to prevent stray light from entering.

System below with plastic 5-gallon buckets used for larval growth trials. They are plumbed in parallel with sump and pump in foreground and head-tank to back. Temperature maintained by ambient air and supplemental heating in sump. We could also cool by introduction of well water. System has be used for numerous trials that have dealt with various aspects of feeding regimen. All subsequent trials will have buckets covered since new location we are unable to control lighting of entire room to serve a single trial.