Rearing of the Milletseed Butterflyfish

The very first success for my project came with collection #3. The egg collectors were set on March 16, 2016. Eggs were harvested the morning of March 17, 2016. There were a total of 20,800 eggs with 11,648 viable (56%). The eggs were stocked at a fairly high density of 58.24/mL into a single 200L flow-through tank. The average rearing parameters for this egg collection was: 26.2 ± 1˚C and 30.0 ± 0.8 ppt. DO was maintained ≥ 6.0 mg/L, and pH ranged from 7.8 – 8.0.

Despite a somewhat low viability, there was a substantial hatch. I checked on the larvae each day, and at three days post hatch, I prepared to administer first feeding as well as background algae. The larvae were extremely tiny and it was hard to distinguish between species at such an early age. I added the first feeding of copepod nauplii, and I did not observe many larvae feeding. I figured this was due to relatively cool water temperature, which was approximately 25ºC at the time.

These larvae developed very slowly, and many died off within the first 5 to 10 days post hatch. Upon examining the larvae, all appeared to have fully developed eyes and mouths; however, many did not have full guts. I wasn’t exactly sure why some of them were not eating, but I continued to feed and monitor accordingly. The water quality checked out fine.

milletseed-25dph

Milletseed Butterflyfish, 25 days post hatch

I was able to take a few good pictures at 25 days post hatch. The post-flexion larvae at approximately 6.13mm looked good. Very well developed eyes and mouth, and completely developed guts full of food. Dorsal spines were forming, and there was an increased amount of pigmentation, with a slight deepening of the body. Perhaps the most important observation was that the larvae had already entered their tholichthys stage of development, with bony plates forming around the head extending back towards the posterior end of the larvae.

Milletseed, 40 days post hatch

Milletseed Butterflyfish, 40 days post hatch

Many of the larvae continued to drop for no apparent reason. The larvae at 40 days post hatch were 7.02 millimeters long, had substantial deepening of the body, and distinct dorsal and ventral spines. Fins were fairly well developed, and the gut was still appeared full of food. The larvae fed on nauplii, enriched rotifers, and newly hatched artemia. The bony plates, characteristic of the tholichthys stage were thicker and more prominent. This “helmet” was clearly visible on the heads of the larvae. Some of the larvae were also beginning to exhibit a silvery appearance.

The larvae continued to dwindle down to only a few. By day 60, there was a single lone survivor. There were a few scares with this larvae, particularly when it was nowhere to be found and was thought to be lost (quite a story). However, it pushed through, and settled at approximately 74 days post hatch.

For fear of losing this special larva, I held off on taking any photos until I knew it completed settlement. By 88 days post hatch, it was clear the mystery Chaetodontid was the milletseed butterflyfish, Chaetodon miliaris. Its juvenile coloration is seen in the following photo.

milletseed-88dph

Milletseed Butterflyfish, 88 days post hatch

It was quite the journey, but this lone survivor was the first of its kind to be reared in captivity, and it too was cute at the about the size of a dime. It had quite the personality and loved being in front of the camera!

Successful Rearing of the Hawaiian Cleaner Wrasse

Egg collectors were deployed on the afternoon of 4/17/16 and collected on the morning of 4/21/16. There was a total of 32,900 eggs with 70% viability. This was the highest number of eggs collected to date. The eggs were stocked at a density of 23.03/mL in a 1,000L flow-through tank. The average rearing parameters for this collection were: 26.8 ± 1˚C and 30.0 ± 0.8 ppt. DO was maintained ≥ 6.0 mg/L, and pH ranged from 7.6 – 7.8.
Most of the larvae Avier examined had well-formed eyes, mouths, and guts, with the yolks fully absorbed. The first feeding of copepod nauplii and background algae was provided. It looked like larvae were either Acanthurid (tang) or Chaetodontid (butterfly). At approximately 30 dph there was a different larva. A very different larva. Pictured at 35 dph, at approximately 8.80 mm in length, was a long and slender larvae, spending most of its time around walls of the tank, picking prey items off the side. The larvae had very well developed eyes, and a fully formed mouth and gut. It did not have a very deep body, but it did have well-formed fins, with blotchy speckles of pigment starting to develop.

Hawaiian Cleaner Wrasse at 35 days post hatch.

Hawaiian Cleaner Wrasse at 35 days post hatch.

The larva was elusive but it showed up again while Avier was cleaning the bottom of the tank a few days later. A brightly colored neon blue streak shot up towards the surface of the tank! He caught the specimen and examined it under the microscope. It was a completely metamorphosed fish. But which fish?? The little guy was moved into a 200L flow-through tank with settled fish from another collection. Pictured at 41 dph, at a length of 13.88mm, the mystery fish had a neon, multicolored strip running from its head to tail, fully developed fins, and a round but slender body dark colored body.

Hawaiian Cleaner Wrasse at 41 days post hatch.

Hawaiian Cleaner Wrasse at 41 days post hatch.

It was  a  Labroides phthirophagus, the Hawaiian Cleaner Wrasse! It was voraciously feeding on enriched artemia, frozen cyclopeeze, and flake. Interesting tidbit, this individual started exhibiting its cleaning behavior at 44 days post hatch (and the other fish in the tank did not like it!).
There is a single mated pair in the entire mix species tank. That pair produced an egg that produced a larva that turned into this fish. This fish is the first of its kind to be reared in captivity, and it has significant implications for the conservation. Pictured at 91 days post hatch,  the juvenile exhibited the narrow mouth, pointed head, and bright colors characteristic of this cleaner species. The multi-colored stripe changed to resemble the distinctive purple coloration found on the adults, and the dark colored body was now jet black.

Hawaiian Cleaner Wrasse at 91 days post hatch.

Hawaiian Cleaner Wrasse at 91 days post hatch.

At 118 days post hatch – the growing juvenile has changed color again. Here’s what he looks like today.

Hawaiian Cleaner Wrasse at 118 days post hatch.

Hawaiian Cleaner Wrasse at 118 days post hatch.

The IUCN reports: Labroides phthirophagus inhabits coral and rocky reef habitats, other than within the surge zone. This species is an obligate cleaner, feeding on the crustacean ectoparasites of other fishes, probably including gnathiid isopods and also on fish mucus. While the population is not identified as endangered, the limited distribution of this fish makes them vulnerable to local environmental damage. As an aquarium fish, captive reared specimens that eat like locusts show great promise for the hobby.

 

Congratulations Avier on a job well done!!

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