Reef Ramblings

3rd September 2012

Over the last few days, starting Thursday 30^th August, we’ve been experiencing what appears to be a run of daily ostracod spawning events. I say ‘appears to be’, as I’ve been unable to find much in the way of details about marine Ostracod reproduction but have found reference to eggs hatching into nauplius larvae which already have a hard shell (Barnes). Otherwise descriptions of ostracod reproduction seems to be vague, describing eggs as being laid in the water as plankton or being attached to vegetation or to the substrate, with some species brooding the eggs inside the parent’s shell. With thousands of species of ostracod it makes identification difficult for anyone other than an ostracod specialist.

Each morning we’ve encountered large numbers of ostracods floating on the surface of a single tank, part of a 1000+ litre, 12-tank critter system. Roughly one millimetre in length and half a millimetre in depth they are forming what I’d describe as an egg raft, with up to a couple of hundred individuals clumping together.

Ostracod ‘Egg Raft’
Midland Reefs ©2012

To be more precise, I should say that they are floating on the surface of the water. This is odd as most small organisms in this size range often have difficulty at the water surface owing to surface tension, a boundary that they are unable to cross, either water to air or air to water. Without intervention small organisms remained trapped by surface tension; localised stirring can breakdown this boundary enabling small organisms to penetrate it and enter the water column.

What is difficult to understand is why these ostracods are on the airside of the water surface as the feed to the tank is below the surface and I can see nothing about the layout of the system that would allow them to be just ‘poured’ onto the surface.

In the reef aquarium ostracods are most commonly seen close to the viewing pane moving around on (and in) the top layer of the substrate. Once harvested from the surface of the water of this single productive tank on the critter system, and mixed into the water column, they quickly settle to the substrate exhibiting the commonly observed behaviour as above.

If we can find out how to intentionally harness this form of reproduction it may prove to be useful in mariculture as another natural food for larval fishes or early juveniles.

I’ve been feeding a proportion of each day’s harvest to our resident population of young clownfishes who are eagerly consuming them.

If anyone out there has an explanation for what is occurring or has had any experience of this phenomenon, please get in touch.

To learn more about ostracods, see Reef Ramblings ‘Zooplankton in the Reef Aquarium – Ostracods’

Tim Hayes

Midland Reefs

©2012

Announcing two new foods for the discerning reefkeeper.

Midland Reefs has just added two new foods to its Reef Scientific range, extending the available range of copepods, RS Frozen Pod-Mix fish & corals and RS Frozen Pod-Mix corals & fish

• RS Frozen Pod-Mix fish & corals, a 700 micron sized copepod mix suitable for most reef fishes and for LPS corals. Roughly equivalent in size to CyclopEeze.

• RS Frozen Pod-Mix corals & fish, a copepod mix containing ‘pods sized from 500 – 700 microns, suitable for feeding finicky corals such as Sea Fans and Gorgonians, Goniopora, and SPS corals, along with smaller reef fishes such as Dragonets or Mandarinfishes. Especially useful for use with fish breeding projects to feed early post larval juveniles, roughly equivalent in size to 2 day old enriched artemia.

A Natural Diet.

The Reef Scientific range of frozen copepods is the nearest thing currently available to the natural diet of the majority of the fishes in the reefkeeping hobby.

Fishes in the hobby tend to be smaller species, say less than 20 cms adult size, with diets mainly comprising copepods along with other small prey items such as fish eggs, fish larva, invertebrate larvae, faeces, etc.

To learn more about copepods and their role in the food chain see: Copepods for the Reef Aquarium. Part 1.

Reef Scientific frozen Calanoid Copepods – The highest quality frozen natural marine zooplankton available anywhere!

High Nutritional Value – High in protein, in omega3, Phospholipids, DHA & EPA, and Astaxanthin.

This range of marine zooplankton is rich in phospholipids, essential fatty acids and proteins along with the caratanoid Astaxanthin. The fatty acid, DHA, is only produced in marine algae and is accumulated in zooplankton as they graze in a process of natural enrichment.

Non-polluting! 100% clean. Needs no pre-rinsing before use. The product is pasteurized for bio-security and sealed, using natural components from crustaceans, minimizing nutrient leakage in the reef aquarium. Can be thawed and kept in the refrigerator for up to 14 days.

Suitable for all saltwater and freshwater fish, corals, and crustaceans.

A number of different species are present in each sizing, providing a rich variety of different nutritional profiles; species include: Temora longicornis, Acartia clausi and Centropages hamatus, Pseudocalanus spp., Paracalanus spp., Microcalanus spp. and early copepodites of C. finmarchicus

Breeding

The smaller-size food particles have a documented positive effect on fish and crustacean larvae.

In co-feeding experiments, clownfish have shown 100% higher growth compared to a diet solely with enriched rotifers and artemia. Survival has increased by 50%.

Dr. Ike Olivotto at the university of Ancona, Italy, has published a paper showing this food to be superior to live feeds such as rotifers and artemia. His research involved comparing two groups of clownfish larvae, one group fed a standard rotifer/Artemia nauplii, diet, the other fed a combination of rotifers/copepod nauplii and Artemia nauplii/copepodites-copepods.

His research showed 100% higher weight along with 30% length increase in clownfishes 10 days post hatching, compared to fish given a diet consisting of enriched rotifers and Artemia. 15 days post hatching, larvae fed with the copepod enhanced diet had a 62% survival rate compared to larvae fed a conventional rotifer/Artemia nauplii diet with a 41% survival rate.

We have used these foods to great success, here at Midland Reefs, raising healthy, well-pigmented, clownfishes, on a diet consisting of rotifers and copepods, whilst completely excluding artemia.

Tim Hayes

Midland Reefs

©2012

I’ve just received my copy of the January 2012 issue of Aquarium Fish International featuring the first edition of my new regular column, ‘The Mariculturist’. The column looks at all aspects of breeding and propagation, covering fish, cnidarians and mobile invertebrates.

For this issue’s table of contents, see: AFI January 2012

You can read the Editor’s Note for this issue by going here.

Also there is some additional online content connected to my column, ‘Fish and Invertebrates Spawned in Captivity’ disappointingly this is an abbreviated version of my full (and ongoing) list, which you can see in full here: List of Ornamental Marine Fishes Bred in Captivity

If there are any areas of mariculture that you’d like to see covered in the column, please get in touch.

Similarly, if you know of any species of ornamental marine fish or invertebrate not included in my list  that has been spawned in captivity, please let me know by contacting me through Reef Ramblings.  Please include any supporting evidence you have, including photos or a reference from a scientific journal.

Update December 15th 2011

I’m happy to say that the list has now been updated on the AFI website.

Tim

Tim Hayes

Midland Reefs

©2011

As per the title, this my first attempt at raising Amblyeleotris randalli larvae, common name – Randall’s Shrimp Goby.

Initial observations:

* Very short hatching period – looks to be 4 days.

* Very small larva – not accurately measured yet but looks to be 2 – 3 mm.

* Going to need a smaller food than standard rotifers.

This one caught me by surprise; I found an egg ball on the substrate on Tuesday morning and then spent an hour faffing about setting up a small brine shrimp hatcher to gently tumble the eggs.

I’ve had the parents for about six years and would estimate their age to be between six and seven. The female is the larger of the pair and also the less timid. Originally living by themselves in a 60 x 30 x 30 tank containing a deep substrate of mixed corals sand and gravel, they spent the last three or four years up until around December 2010 with an Alpheus bellulus snapping shrimp. Up until then the tank had always been a busy place with the shrimp digging and improving the tunnel system shared with the gobies whilst the female kept watch out in the open with the smaller male staying in the background close to a tunnel entrance. The shrimp was fairly tame, even on occasion accepting food from my hand, the female fish, while wary, would dash out for food with the male cautiously following the lead of his mate

In early December I noticed that the tank seemed to be devoid of life; there was no sign of shrimp nor gobies but given the tunnel system where they could away id decided to watch carefully while continuing to add a reduced ration of food.

Finally I spotted one of the gobies reflected in the back glass; just a head was peeking out from a tunnel hidden from the front of the tank by a rock, over the following days I continued to spot one fish, then the other, for very brief periods, usually via the reflection. I came to the conclusion that the shrimp had died, most likely from old age, and that with out their companion the fish were feeling vulnerable and were spending most of their time hiding. This behaviour has continued so far this year.

Over the years I’ve had these fish I’ve always assumed that they were spawning as the figure of the female would wax and wane as she built up eggs and, presumably, laid them. This recent discovery of an egg ball is the first proof of this.

The larvae hatched on Saturday morning but when I examined the hatcher I found that a sizable proportion of the larvae were dead. Why, is unknown, possibilities include:

• Too vigorous aeration.
• Poor water quality.
• Poor quality of eggs as a result of recent parental behaviour.

It’s also worth considering whether the parents had discarded the eggs as this is the first time an egg ball has been observed, although having said that I would have expected the parents to eat their own eggs if they felt that they weren’t going to hatch. This is common behaviour for many fish species.

Not having any large supply of rotifers to hand, much of Tuesday was spent setting up multiple rotifer cultures ready for the hatching but on Saturday morning, seeing the small size of the newly hatched larvae, it was obvious that something smaller was required. Despite managing to hurriedly isolate some ciliates for use as a first feed and as a starter culture no larvae remained alive Sunday morning.

In preparation for future spawnings, I’ll continue to maintain ciliate cultures and look to starting a culture of small strain rotifers. I’m also considering deploying a larval trap in case the main problem with this spawning was excessive buffeting of the egg mass.

Tim Hayes

Midland Reefs

©2011