Lionfish stoppped feeding

[Deepblue10]

Hi everyone, I'm really hoping someone can help me with this one... I'll give as much info as I can about the tank etc.

I have a 2metre x 60cm x 60cm mature (3 years old) marine tank with large skimmer, 2 external filters, 2x 25Watt UV sterilisers and 2x twin 55watt T5 light units.
In the tank I have two Volitans Lionsfish, one is 25cm and the other around 13cm. The larger lionfish I have had for over 2 years and was bought as a youngster. The other lion is a more recent addition, and has been in for about 1 month. The larger lionfish has always eaten very well, and enjoyed a mixed diet of lance fish, mussels, cockles etc. however in the last couple of months it has been more reluctant to take food, and seems disinterested in it altogther now.
I have tried feeders but these are watched and not eaten, I have also tried some sugestions that were made to me like increasing the temperature slightly, adding an attractant like garlic based product directly to the food, and to the tank water.
The rountine maintenance I do on the tank is 25% water change with RO water every week. The tank also contains a selection of soft corals and several types of desirable algae.
I test the water each week and the readings are very stable, Ammonia nil, nitrite nil, nitrate 5ppm, pH 8.2. Specific gravity is 1.023.
I am at a loss as to why the larger lionfish has stopped eating, this began before I introduced the smaller lionfish, and this fish is feeding very well. The condition of the larger lionfish is fine, no diseases etc but now it is starting to look very lean as it has only taking very small amounts of food in the last month.

I would be really grateful for any advice anyone can offer, and I am happy to give any more information that I may have not included in this post...
Thanks in advance!

[AQTCJAK]

Lions can be a very dificult fish to feed to include changing there intake needs on thier own. I have had great sucess when this happen to get them to eat HBH Super Soft Krill pellets the larger the better. I entice them to the water flow & then 1 pellet maybe 2 @ a trime they attack & eat very well.

[leebca]

Sorry to hear of the problems. There may be several reasons why a fish stops eating. Sometimes we just don't know. However, it usually can be summed up in a small list:

1. Tired of the same old foods, nutritional issues;
2. Environment/water quality issues and chronically short on space;
3. Tank mates;
4. Internal disorders;
5. Disease;
6. Unknown (end of life/old age)

1. Your food/feeding list is short. I would like to see the whole list. You list mussels (freshwater?) and cockles and lancefish which are usually saltwater. The three don't make for a good variety. You don't mention stuffing these feeds with additional vitamins, or fat supplements that these fish in captivity should be given. You don't mention how these foods come to be presented (taken out of shell, fresh, how the shell was opened, what it is you're buying, etc.). What did the fish last eat -- I mean the very last thing the fish ate? and the two meals it had before that? How often was it fed? I'd be interested more in these answers since your post is thin in this area.

2. There is more to water quality than just the test kits, but i don't see any evidence of why there should be a concern there. You did not indicate the alkalinity, calcium, and magnesium levels in the water. I'd like to know what they are at this time, not yesterday or last week. I'd like to know the temperature and more specifically the temperature range (the highest it gets and the lowest it gets) during a 24-hour time. I don't think there is a space issue here, the tank seems large enough for the marine life.

3. Lionfish sometimes like to 'perch' on things. Is there any change a tank mate didn't like being perched upon?

4. Hard to say. I've performed postmortems on Lionfish and they do suffer a greater than average share of internal disorders, usually because of diet, lack of nutrition and/or the wrong nutrition. Had this fish ever been de-wormed? What does its feces look like? Although thin as you pointed out, is the abdomen uniform in shape -- that is, no ripples, bulges, or swollen areas? A photo would be helpful to me in this area.

5. Sometimes tied in with 4. Though the reduced eating rate began before the introduction of the last Lionfish, it could be that it or a previous addition brought in something with it. You don't mention using a quarantine system for fish and marine life, so anything could have found its way into the aquarium. The thing about captive fishes held for years is that they lose much of their ability to fend off disease, which can be even as little as 'new' bacteria coming into the aquarium. This ties in with nutrition issues.

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Fish can sometimes be encouraged to begin to eat by going through a very large (60%+) water change. I would prepare to do this as soon as the water is ready. Just to be on the safe side, check your source water quality, RO membranes do get old. Just be sure to make the water change properly: How to Make a Successful Water Change. This will help should there be an unseen water quality issue.

I will wait to hear more answers and then any evidence that the water change has altered the behavior of any (including the Lionfish) inhabitants of your system. Did they 'perk up' any after the change?

Good luck!