The Substrate Sifting Gobies:
Fishes that Earn Their Keep 

By J. Charles Delbeek and Scott W. Michael 

One trend that has gained favor with miniature reef hobbyists is 
to use minimal or no substrate on the bottom of their aquariums. This 
is not to say that a substrate cannot be used, only that not using it 
makes maintenance easier. Poorly maintained substrates, however, tend 
to accumulate detritus quickly and if this is not dealt with, 
anaerobic (oxygen poor) areas could develop as bacteria use oxygen to 
break down the detritus further. This can eventually lead to major 
problems. Detritus often acts as a source of phosphate as bacteria 
decompose it and release stored phosphates. These phosphates then act 
as nutrients for undesirable algae growth such as "hair algae" 
(Derbesia) and "slime algae" (cyanobacteria). As there are 
still hobbyists who use undergravel filters with relatively thick 
substrate beds and others who would like to use a substrate in their 
reef aquariums for aesthetic reasons, it is important to find a way to 
deal with detritus. 

There are several strategies one can use to reduce detritus 
accumulation in coarse marine aquarium substrates used with 
undergravel filters. You can periodically stir the substrate and 
siphon out accumulated detritus when doing water changes. This is 
often tedious and time consuming in a large, heavily stocked aquarium. 
Powerful water currents, directed along the surface of the substrate, 
can also help to prevent detritus from settling on the bottom. This 
keeps detritus in suspension where it can be removed by external power 
filters or an overflow. Still, every aquarium has its dead spots and 
some particulates are not so easily carried along by water currents. 
Neither of these methods deal adequately with detritus accumulation 
underneath decorations or live rock.

If you wish to use a substrate in a reef aquarium without an 
undergravel filter, the grains must not be large enough to allow 
detritus and mulm to accumulate within and under it. The commonly sold 
coarse crushed coral is not suitable. Much better would by fine coral 
gravel or coral sand (2-4mm dia.). The layer can be anywhere from 1 to 
10 cm thick. A substrate in a reef aquarium with live rock and corals, 
can play a beneficial role by supplying a refuge for small 
crustaceans, worms and other organisms that help to decompose waste 
and can act as a food source for fish. The larvae of these organisms 
will also contribute to the planktonic population of the aquarium and 
can act as a food source for other invertebrates. Anaerobic layers may 
develop in the substrate and, provided the organic load of the 
aquarium is not too great, can provide further denitrification. If the 
organic load of the water is too great, hydrogen sulfide production 
will occur.

Many of the options listed above for keeping coarse substrates clean 
can also be used in reef aquariums with finer substrates. However, 
when using fine substrates, there are other, biological options, 
available to the aquarist. Perhaps you should employ the help of 
nature's "clean-up crew" and let them facilitate your efforts in 
maintaining an optimal environment for your invertebrates?

Coral reefs are such diverse environments that few niches (roles in 
the environment) go unused. For example, there are many organisms that 
use the sandy substrates that surround coral reefs, for food and 
shelter. These include various shrimp, starfish, sea cucumbers, 
brittlestars, sea urchins and fish. In Europe, the majority of reef 
aquariums use such organisms to help maintain healthy, calcaerous 
substrates. Although there are hundreds of different invertebrates and 
fish that dwell in these communities and can be used in such a manner, 
we will concern ourselves with only a few fish species that can be 
normally found in aquarium shops. These fish generally feed by sifting 
mouthfuls of fine substrate through their gills and straining out 
edible infauna such as worms and small crustaceans. In doing so they 
help to keep the substrate from becoming packed with detritus and 
overgrown with algae. As an added benefit, as they pass the sand out 
through their gill slits, any detritus will be resuspended and carried 
away by water currents into your filter or overflow. One drawback to 
these fish is that they can deposit substrate onto bottom dwelling 
invertebrates such as corals and anemones. Therefore, it is best not 
to have certain sessile organisms on the floor of the aquarium. Yet, 
some such as the normally bottom dwelling hard corals Fungia 
spp., Heliofungia spp., and Herpolitha spp. (Mushroom or 
Plate and Slipper corals respectively), can easily shed any substrate 
that may fall on them. As an example of this philosophy, SeaWorld of 
Ohio employs a pair of Yellow-Headed Sleeper gobies in their reef 
tank. These fish keep the coral sand substrate free of microalgae and 
maintain a sparkling clean appearance (P. Mohan, personal 
communication; C. Delbeek and S. Michael, personal observations). 

Most of these living "vacuum cleaners" belong to the family Gobiidae. 
This is the largest family of marine fishes in the world, containing 
over 2000 species. In the Indo-Pacific alone there are some 200 valid 
genera and 550 species (Myers 1989). In this article we will cover 
three genera that are commonly found in aquarium stores that can be 
used, to varying degrees, to help maintain aquarium substrate. They 
are the Hover Gobies, Amblygobius spp., the Signal goby, 
Signigobius biocellatus, and the Sleeper Gobies, 
Valenciennea spp. 

Members of these genera are known as fossorial, which means that they 
will make or use the burrows of other organisms as shelter. In the 
aquarium the lack of suitable bottom substrate and pieces of rubble 
(important in the burrow infrastructure) may make it difficult for 
these fish to construct their own homes. The aquarist can assist by 
creating artificial burrows with siphon tubes. Just cut off half of 
the rounded end of the tube so when it is laying flat on the aquarium 
bottom, the opening is directed toward the surface. Cap the other end 
and bury the tube under gravel, rocks or debris. To give the burrow a 
more natural appearance pieces of coral rubble or sand can be 
siliconed around the open end. Make sure the burrow diameter is at 
least twice the girth of the potential fish occupant. 

Hover Gobies (Genus Amblygobius)
These small fish (4.5-12 cm in length) are generally found over sand 
areas but some species also occur on hard bottoms. There are at least 
nine species in this genus, but the species most often encountered in 
the aquarium trade are Hector's Hover goby, Amblygobius hectori 
(Smith, 1956), Phalaena's Hover goby, A. phalaena 
(Valenciennes, 1837) and Rainford's Hover goby, A. rainfordi 
(Whitley, 1940). All three species spend a great deal of time hovering 
close to the bottom, constantly picking at the substrate and spitting 
out quantities of sand and detritus. Amblygobius phalaena and 
A. hectori use the burrow of a shrimp or another fish in the 
substrate or under rocks while A. rainfordi does not use a 
burrow and is often observed swimming over coral growth. In the wild, 
Phalaena's Hover goby is observed singly and in pairs, and often 
shares a burrow with Sleeper gobies or juvenile surgeonfish (Paulson 
1978; S. Michael, personal observation).

Aquarium Behaviour
In the aquarium, these fish prefer peaceful surroundings with numerous 
hiding places. When kept in a tank with large active fish they may 
hide most of the time and may not get enough to eat. Of these three 
species, A. phalaena is the most easily maintained and is also 
the best substrate sifter. It is generally a good feeder, accepting 
most types of foods, and Myers (1989) reports that it consumes large 
quantities of algae. Rainford's Hover goby is also a vigorous algae 
eater, browsing on filamentous red and green algae. This species and 
A. hectori will do poorly if kept with aggressive tankmates and 
do best in aquaria with a good supply of filamentous algae. Both of 
these fish readily accept live black worms and live brine shrimp, and 
with perseverance they can be switched to more nutritious frozen 
preparations. 

The members of this genus tend to be non-aggressive toward other 
species and will not bother any invertebrates, which makes them an 
excellent candidate for the reef aquarium. The only problem they may 
have in large reef tanks that lack filamentous algae is getting enough 
to eat. A. phalaena can be kept in male-female pairs quite 
easily but any more than two individuals of the same species or genus 
will fight constantly, resulting in the death of subordinates 
(Achterkamp 1991; S. Michael, personal observation). This apparently 
holds true for the other fish in this genus as well. The little 
experience the authors have had with A. hectori suggest it is 
shy and can be difficult to feed.

Breeding Behaviour
Achterkamp (1991) provided details of the breeding behaviour of A. 
phalaena and it is likely that the other species behave similarly. 
Adult male A. phalaena (approx. 12 cm) can be distinguished 
from females by several black dots on the tail fin. When spawning time 
approaches, the pair will search throughout the aquarium for a 
suitable nesting hole, greatly disturbing the substrate in the 
process. Once the nest has been built, egg laying begins, usually at 
night. Several large clumps of eggs are deposited that consist of 
hundreds of dirty yellow-white eggs. After egglaying the male defends 
the nest vigorously and may even drive away the female. After about 6 
days the eggs hatch out and the pair ignore the offspring as they rise 
to the surface. A pair may breed several times a month or only once or 
twice a year. If anyone has any information on the behaviour and 
breeding of the other species in the genus, we would like to hear from 
you!

Signal Gobies (Genus Signigobius)
The Signal goby, Signigobius biocellatus (Hoese and Allen 1977), is 
the only species in this genus and is easily identified by the large 
black eye-spots (ocelli) on the anterior and posterior dorsal fins. 
The Signal goby occurs in sheltered lagoons on sand and coral rubble 
substrates and occupies burrows that they excavate by using their 
mouth to carry away sand and shell fragments and by going head first 
into the hole and vigorously beating their tails (Hudson 1977). The 
burrow is used for shelter and reproduction. Juveniles occur singly 
while adults (7.5 cm) are always found in pairs (Debelius 1986). They 
feed in a similar fashion to the Hover gobies, taking in mouthfuls of 
sand and sifting it through their gill-rakers. 

These fish move by hopping along the substrate. They frequently flick 
the two dorsal fins forward exposing the large ocelli present on the 
dorsal fins. If a predator or rival approaches the Signal goby will 
erect its fins, arch its back and tilt its body. The lateral view of 
this goby apparently mimics the "face" of a piscivorous fish and may 
discourage a predator from attacking. It has also been suggested that 
this lateral perspective as well as the hopping behavior and the fin 
flicking resembles a crab moving over the bottom (Hudson 1977). 

Aquarium Behaviour
Personal observations, discussions with other aquarists, and 
examination of the literature all indicate that this is not an easy 
species to maintain. You will usually see them offered for sale as 
pairs and we recommend you buy them this way. If they are separated, 
they usually do not live long. They should be kept in an aquarium 
with fine substrate but some added coral rubble will facilitate their 
burrowing behaviour. This species should also be provided with 
numerous hiding places. Live brine shrimp and black worms can be used 
to induce feeding in finicky individuals, but vary the diet as much as 
possible once they are eating. They should be fed AT LEAST twice a day 
in order for them to maintain their body mass. Signal gobies should 
not be kept with aggressive tankmates (e.g., dottybacks, large 
wrasses), especially in smaller aquaria; they tend to do much better 
in a tank of their own (G. Schiller, personal communication).

Breeding Behaviour
The breeding behavior of the Signal goby is very unique and has been 
documented in the wild and the aquarium by Hudson (1977). As mentioned 
previously they form monogamous pairs and share a burrow. The gravid 
female nibbles the male's body before spawning and then enters the 
burrow and deposits her eggs. After spawning the male is sealed in the 
burrow at which time he fertilizes the eggs, guards and possibly 
aerates them. For two to three days the male resides in the burrow. 
During this period the female will occasionally open the chamber and 
liberate the male and the pair will engage in burrow maintenance. The 
male then re-enters the burrow and is once again sealed in. Eventually 
the male exits the burrow one last time and both parents close the 
entrance and move to a new burrow or reopen an old one nearby. The 
parents occasionally visit the "nursery" burrow, open it, clean it of 
debris and irrigate it with fresh seawater by entering the burrow 
tail first and slowly beating their tails. Finally, the burrow is 
opened a final time and a single juvenile fish emerges. It has not yet 
been determined how the developing young fish is nourished within the 
burrow but is has been suggested that they depend on yolk reserves, 
feed on micro organisms, or possibly one embryo develops faster than 
the others and feeds on its broodmates (Hudson 1977)!

Sleeper Gobies (Genus Valenciennea)
There are approximately 15 species of this genus in tropical waters, 
ranging in size from 5 cm to 20 cm (Debelius 1986). A number of 
species frequently make their way into the tanks of marine retailers, 
they include: the Yellow-headed Sleeper goby, Valenciennea 
strigata (Brousonet, 1782), the Maiden or Diamond Sleeper goby, 
V. puellaris (Tomiyama, 1955), the Banded or Tiger Sleeper 
goby, V. wardi (Playfair & Gunther, 1886), the Sixspot Sleeper 
goby, V. sexguttata (Valenciennes, 1837), the Two-stripe 
Sleeper goby, V. helsdingenii (Bleeker, 1858), and the Long-
finned Sleeper goby, V. longipinnis (Lay & Bennett, 1839). We 
have included a table with information on the maximum size and the 
distinguishing characteristics of the above listed members of this 
genus.

These gobies feed primarily on tiny crustaceans (usually under 1 mm in 
length) and occasionally on minute gastropods, clams, foramineferans, 
and polychaete worms (Hiatt & Stratsburg 1961, St. John et al 1989). 
Some of the larger species, like the Yellow-headed Sleeper, may on 
rare occasion eat small fish (Hiatt & Stratsburg 1961). A study on 
the Long-finned Sleeper goby documented that this fish will take bites 
out of the bottom sediment to a depth of 3 cm at a rate of about six 
bites per minute during the day (St. John et al 1989). As far as 
aquarium clean-up is concerned not all sleeper gobies are created 
equal. Some are more aggressive substrate sifters than others. For 
example, the authors have found that the Maiden Sleeper and the Long-
finned Sleeper are more effective at displacing bottom sediment than 
the Banded Sleeper and the Two-stripe Sleeper. 

The size of the Sleeper goby burrow varies from one species to the 
next. In the case of V. sexguttata the burrow is 10-15 cm 
long, with a coral rubble roof and a rectangular floor plan (Paulson 
1978). In the larger Yellow-headed sleeper up to 6 liters of resin was 
required to fill one burrow (Paulson 1978)! The burrows of some 
sleeper gobies provide sanctuary for other fish as well the resident 
gobies. For example, juvenile convict surgeonfish (Acanthurus 
triostegus) refuged in 2% of all V. sexguttata burrows 
observed near Enewetak Atoll. Twenty percent of all V. 
puellaris burrows examined contained juvenile yellow tangs 
(Zebrasoma flavescens). Small groups (of 2-20 individuals) of 
Green Torpedo gobies (Ptereleotris microlepis) were observed to 
hang above the entrances of Sixspot, Maiden, and Long-finned sleeper 
goby holes and to disappear into the burrows when a predator 
approached (Paulson 1978; S. Michael personal observation). 

Some species of Sleeper gobies have interesting defensive behaviours
that the aquarist may encounter. For example, juvenile V. wardi
have one spot on their dorsal fin and one on their caudal fin and,
like the Signal gobies, mimic the head-on perspective of a predator
when viewed from the side. When threatened, the Banded Sleeper
presents his side toward the predator and raises his dorsal fin and
spreads his tail, displaying the eye-spots (S. Michael, personal
observation)!

Aquarium Behaviour
Sleeper gobies usually pair for life when they are young (Debelius 
1986). Usually the pair occupies a burrow on its own, but sometimes as 
many as ten sleeper gobies, representing several different size 
classes, will utilize the same burrow (Paulson 1978). Sleeper gobies 
are sometimes sold as pairs and the authors recommend that you buy 
both individuals in such cases. If you have a single specimen you 
should try to find it a companion as they apparently do better in 
pairs; their pair bonding behaviors are also fascinating to observe. 
Most sleeper pairs are easy to recognize as they swim very close 
together through the tank, with the lower jaw of one touching the 
upper surface of the head of the other. They look like a figure 
skating pair as they "waltz" through the aquarium together! Males are 
easily distinguished from the female as they have an elongated second 
dorsal spine similar to the mandarin dragonet (see Delbeek 1989). 

Some sleeper gobies spend most of their time hovering above the bottom 
(e.g. Yellow-headed Sleeper goby), while others are most often 
observed prone on the substrate (e.g. Maiden Sleeper goby, Banded 
Sleeper goby). Some sleepers are also more secretive than others. 
For example, the aquarist may go without seeing a newly introduced 
Banded Sleeper for weeks and when this sleeper does show itself it is 
often for very brief periods of time. 

When first introduced in the aquarium it is not unusual for sleepers 
to hide for several days as they become acclimated to their new 
surroundings. Once they have overcome their initial shyness they will 
go about the chore of building their home. This usually consists of 
excavating a hole under a rock that both will share. It is important 
to arrange your decorations in a stable configuration or else you may 
find your delicately balanced decorations lying in a jumbled heap on 
the bottom! Not only does the feeding behavior of the sleeper gobies 
help put detritus into suspension, their active burrowing under 
aquarium decor also proves beneficial in this regard. When evening 
comes the pair will retreat to their burrow and the male will create a 
small pile of rocks at the entrance or plug it with a ball of algae to 
block it off for the night. Once they have survived for several 
months without any problems, your sleeper gobies should live for many 
years (Achterkamp 1986).

Sleeper gobies will eat most foods offered but it may take a few weeks 
before they will accept prepared foods. They are particularly fond of 
small crustacean (e.g., brine shrimp, mysis) and blackworms, but feed 
them a varied diet. It is also possible that some species may feed on 
larval and juvenile bristleworms, although they have been seen to 
ingest and then spit out adult worms (S. Michael, personal 
observation). Since many of the sleepers are active fish that can grow 
to at least 20 cm in length. they must be kept well fed or else they 
will slowly waste away. Therefore, it is important to have a good 
filtration system, preferably enhanced by the presence of a protein 
skimmer, to deal with the considerable amounts of waste products that 
they produce. 

Breeding Behaviour
As mentioned above, male sleeper gobies are easily identified by their 
elongated second dorsal spine. The female generally lays about 2000 
eggs on the roof of their chamber. She will tend the eggs for 3 weeks 
during which she will not leave the chamber. Just before hatching 
occurs the male will seal the entrance to the chamber, sealing in the 
female. After the eggs have hatched the male will reopen the chamber, 
at night, freeing the 2 mm fry (Debelius 1986). We have not read any 
reports of successful rearing of the fry but it seems that it may be 
possible given enough time and patience.

Sleeper gobies, Hover gobies and Signal gobies can help the aquarist 
to maintain a clean and healthy substrate, however, one may still have 
to perform the odd stir-and-siphon routine if problems develop. 
Although most of these fish are active sifters they cannot do so with 
a substrate that is too large such as dolomite or crushed coral. In 
fact, these fish may injure themselves trying to handle substrate that 
is too large or coarse, and bacterial infections may result. The best 
substrates to use have grain diameters less than 2 mm in diameter, 
such as coral sand or finely crushed coral. As mentioned above, in 
order to aid in burrow construction some larger sized pieces should be 
mixed in with the finer to provide "building-blocks" for the fish.

References
Achterkamp, A. 1986. Bewust kiezen... een serie praktische          
aquariumtips/4. Het Zee-Aquarium 36(5):92-93.

-------------- 1991. Bij de voorplaat... Amblygobius phalaena. 
Het Zee-Aquarium 41(5):104-105.

Debelius, H. 1986. Fishes for the Invertebrate Aquarium. Reimar 
Hobbing GmbH, Essen.

Delbeek, J.C. 1989. The Mandarin Fish: Synchiropus splendidus 
(Herre). Seascope Vol 6 (Fall):1,3.

Hiatt, R.W. and D.W. Stratsburg. 1960. Ecological relationships of 
fish fauna on coral reefs of the Marshall Islands. Ecol. Monogr., 
30:65-127.

Hudson, R.C.L. 1977. Preliminary observations on the behaviour of the 
gobiid fish, Signigobius biocellatus Hoese and Allen, with 
particular reference to burrowing behaviour. Z. Tierpsychol., 43:214-
220.

Paulson, A.C. 1978. On the commensal habits of Ptereleotris, 
Acanthurus, Zebrasoma with fossorial Valenciennea 
and Amblygobius. Copeia, 1978:168-169.

Myers, R.F. 1989. Micronesian Reef Fishes. Coral Graphics, Guam. 

St. John, J.,G.P. Jones, and P.F. Sale. 1989. Distribution and 
abundance of soft-sediment meiofauna and a predatory goby in a coral 
reef lagoon. Coral Reefs 8:51-57.



Table 1. Commonly imported Sleeper gobies.

Species           Description                 Max.      Distribution
                                              Length
_________________ __________________________  ______   _______________

Two-stripe        body white with a pair of   16 cm    East Africa to  
sleeper goby      brownish orange stripes     (6.3 in) Western Pacific
(V.               from the head to the tail,  
helsdingenii)     black spot on first dorsal 
                  fin                        
                   

Long-finned       body white with stripes     15 cm    Eastern Indian            
sleeper goby      consisting of rust-orange   (5.9 in) Ocean and 
(V.               colored dashes and brown             Western Pacific  
longipinnis)      spots, also a row of five           
                  blue-edged horseshoe shaped
                  markings on lower section  
                  of body                    

Maiden or Diamond body tan or light grey      14 cm   Red Sea to      
sleeper goby      with orange stripe,        (5.5 in) Samoa and the   
(V.               edged in blue from the              Marshall Islands
puellaris)        mouth to the tail and 
                  orange spots on the   
                  upper part of the body

Six-spot          body white; 6-8 small       14 cm   East Africa to  
sleeper goby      blue spots on cheek and    (5.5 in) Samoa and the   
(V.               gill cover                          Marshall Islands
sexguttata)


Yellow-headed     body light grey, head       18 cm    East Africa to        
sleeper goby      yellow, blue streak behind (7.1 in)  Society Islands
(V.               and under eye
strigata)    
          
Banded or Tiger   body with alternating       11 cm   Indo-Pacific and    
sleeper goby      brown and white bands,     (4.3 in) Western Pacific 
(V. wardi)        blue line under the eye,      
                  black eye-spots present 
                  on dorsal and caudal fins