Mudskippers—marvels of the mud-flats!
If you have ever seen a wildlife documentary on tropical mangrove swamps, you will likely have observed mudskippers at work and play. These unusual fish, about 15 cm (6 in) long, are a type of goby.1 Swimming in water, they seem no more remarkable than other fish. However, once the tide goes out to expose the mudflats, it’s a different matter altogether.
Comedians among fishes
Mudskipper antics on land are certainly amusing to watch. To move along, a mudskipper will slump forwards by doing ‘press-ups’ with its pectoral fins, a type of locomotion called ‘crutching’.2 When two male mudskippers dispute territory, they press up on their pectorals with mouths agape, making sideways head-swipes at each other. This comical sight was amusingly captured on acclaimed wildlife TV series, Life.3 Most dramatically of all, a mudskipper may try to attract the attention of a mate by an impressive leap into the air, followed by an ungainly landing!
A creationist’s worst nightmare?
A fish that spends more of its life on land than in the water and ‘walks’ (after a fashion) on its pectoral fins is certainly an oddity. Some evolutionists have pounced on the mudskipper as allegedly providing evidence against biblical creation. On a well known anti-creationist website, one blogger gleefully responded to a picture of two Indonesian mudskippers with the comment: “Oh no! The creationists’ worst nightmare: a walking fish!”4
An on-line video also exults in this as a major ‘Creationist’s Nightmare’.5 Among the reasons given are mudskippers’ unusual method of breathing and their unique eyes. However, the coup de grace, according to certain evolutionists, is that “the front fins can barely be called fins anymore: they are clearly an in-between of fins and more complex legs, to walk on land.” The triumphal conclusion reached? “Knowing all this, how can you ever claim that there are no transitional species?”
Accepting the challenge
Contrary to these confident claims, this unique and fascinating amphibious fish is in no way troublesome to those who view Genesis 1–11 as literal history. Periodically, Creation magazine has dealt head-on with evolutionary notions about weird and wonderful fish and fish-like animals, such as the axolotl6 and the handfish,7 similarly claimed to be evolutionary transitions or throwbacks. So, what about mudskippers?
Their robust pectoral fins are distinct from those of most other gobies, possessing double-jointed movable hinge joints. The fin muscles are also unusual, being divided into sections that move the upper and lower fin rays independently.8 Studies have shown that their fin-rays are partially collapsed when moving over land but are positioned to give maximum foothold on the mud.9 The anatomy and deployment of these fins gives them the much-needed strength, flexibility, control and range of movement for the mudskipper’s mudflat lifestyle. Slow and gradual evolutionary modification of these crucial organs of movement would require many information-adding mutations to occur in just the right places at just the right times—mutations to alter the musculo-skeletal system, the wiring of the nerves and, most importantly, the embryological development of the fins. Instead, extensive research into these kinds of complex specified genetic changes provides no evidence that they can occur, let alone in such coordinated coincidences as would be required.10 Also, each such mutation needs to provide a distinct advantage to the fish in order to be ‘locked in’ by natural selection. The likelihood of all this is vanishingly small.
The fish that blinks
Specializations of eyes in living creatures are often claimed to demonstrate the truth of evolution, but nothing could be further from the truth. For example, the surface-swimming Anableps (a fish possessing eyes with the equivalent of bifocals)11 and the deep-sea brownsnout spookfish (with its telescopic eyes that look two ways with the help of mirrors!)12 are both creatures whose eye designs cannot be accounted for by just-so story-telling.
Mudskippers have excellent all-round vision,13 which makes perfect sense for a creature that could easily become a tasty snack for predators, and argues against the slow evolution of this feature over millions of years. All mudskipper species have prominent eyes positioned on top of the head, more forward-facing than in most other fish. This gives them limited stereoscopic vision, allowing depth perception as in human beings. External eye muscles form a hammock-like seat for the eyes, allowing them to be raised or depressed at will14 and even to be completely shut inside liquid-filled skin ‘cups’ when necessary. This feature is essential to keep the eyes moist, and makes them unique as fish which blink!
The light-sensitive retina of each eye is ‘ramped’ so that it is further from the lens towards the top of the eye.15 This means it can focus on objects at different distances with the upper and lower parts of the eye, a useful feature for a fish that is in and out of the water so much.
For any one of these complex specializations to arise by unguided genetic mistakes is unlikely to say the least. Considered altogether, these features of mudskipper eyes represent a brilliant design solution to their peculiar lifestyle. Just suppose that protruding eyes had somehow evolved but the special moisturising cups had yet to appear and/or the special lens-retina relationship had yet to arise. Fish trying to make it on land but which couldn’t properly focus on objects, and whose eyes were liable to damage by drying out, would have been hugely disadvantaged—and less fit to survive.
Skin breathing specialists
Mudskippers do not breathe through their gills, which are used instead to excrete waste products such as ammonia.16 Rather, gas exchange occurs across the entire skin surface, which must be kept moist for the purpose. This includes the inner linings of the mouth and throat which, like our own lungs, are moistened surfaces lined with blood capillaries. Mudskippers may gulp mouthfuls of air by enlarging the throat cavity while closing a special valve to the gills. While under water they are, in fact, less efficient at gas exchange than most other fish so their heartbeat and general metabolism must be slowed down to conserve oxygen. This suite of special features for breathing air makes good sense in a creature that lives the mudskipper’s life. However, try contemplating how the blind forces of evolution could gradually have changed a gill-breathing fish (perfectly adapted to life in water) into a mouth and body surface-breathing amphibious fish. At every one of the numerous intermediate steps away from a true fish, anatomical and physiological challenges would rear their ugly heads, making any claimed survival benefit wishful thinking.
Nothing was left to chance in the mudskipper’s design. For instance, fish in general must maintain a slimy mucus coat as a barrier against various parasites. This is much more important for mudskippers when sliding about on land and through their burrows (see box). Mudskippers’ mucus does more than just lubricate their skin, reducing drag. Recent research has shown it also has antimicrobial activity against a wide range of bacteria.17 This includes many which infect humans, so studying the mucus could benefit mankind.
Mudskippers affirm creation!
Mudskippers really are marvels of the mangrove swamps and mudflats. Whether we focus on their special eyes, take in their unique breathing or ponder their amusing fin-walking, these fish seem to have an ideal blend of characteristics for creatures that are at home in water and on land. Their various ‘departures’ from normal fish anatomy show an economy of design, with the complex parts of each body system all clearly specified (by instructions in the DNA) and finely tuned. Mudskippers are certainly no reason for creationists to have bad dreams! Those who choose to believe otherwise would appear to be willingly ignorant (2 Peter 3:5).
- Over 30 species of mudskippers exist (in five genera) and make up the bulk of the subfamily Oxudercinae, classified within the family Gobiidae (gobies). The specialization in mudskippers makes it unlikely that all gobies are the same created kind, however.
- Mudskippers in the genus Periophthalmus make popular pets and aquarists like to feed them insects, spiders and other live foods by hand.16
- Average adult size depends on the species, from 15 to 25 cm (6–10 in) long.
- Mudskippers have many specializations for amphibious life (see main article). For instance, on land, they excavate J-shaped burrows in which they may raise their young.
- Digging burrows involves carrying mouthfuls of soft mud and spitting them out at the surface—a constant job in an intertidal zone!3
- The mud and burrow water is very poor in oxygen, so outside air is gulped down and released in the upturned section of the burrow to aerate the eggs.18
References and notes
- Other names are ‘kangaroo fish’ and ‘johnny jumpers’. Return to text.
- This is because it resembles a person moving along on crutches. See: Pace, C.M. & Gibb, A.C., Mudskipper pectoral fin kinematics in aquatic and terrestrial environments, J. Exp. Biol. 212(14):2279–2286, July 2009. Return to text.
- See clip from Episode 4 ‘Fish’ of this BBC series, hosted by David Attenborough, on YouTube, accessed 12 August 2011. Return to text.
- On pandasthumb.org, accessed 12 August 2011. Return to text.
- Accessed on YouTube August 2011. Return to text.
- They can transform (over a few weeks) from an aquatic to land-based lifestyle, including shrinkage of their gills and an increase in lung function. Dykes, J., The Axolotl: The fish that walks? Creation 27(4):21–23, September 2005; creation.com/axolotl. Return to text.
- May, K., Rare Australian fish has fins like hands, Creation 28(3):28–29, June 2006; creation.com/handfish. Return to text.
- Ref. 2, p. 2279. In other gobies, these abductor superficialis muscles are single (non-divided) muscles. Return to text.
- Ref. 2, p. 2285. Return to text.
- See chapter 5 of Sarfati, J., Refuting Evolution 2, Creation Book Publishers, 2011. Also available at creation.com/re2-beneficial-mutations. Return to text.
- Grigg, R., The fish with four eyes (Anableps), Creation 18(1):52, December 1995; creation.com/anableps. Return to text.
- Sarfati, J., Four-eyed spookfish has mirror eyes, Creation 31(4):32–33, September 2009; creation.comc. Return to text.
- Their visual fields are nearly 180 degrees for each eye! Return to text.
- Schwab, I.R., Janus on the mudflats, British Journal of Ophthalmology 87(1): 13, 2003. Return to text.
- See www.mudskipper.it/VisMech.html, as at 12 August 2011. Return to text.
- Much information in this paragraph is courtesy of Polgar, G., Mudskippers: an introduction for aquarists, wetwebmedia.com, as at 12 August 2011. Return to text.
- In many fish, antibacterial action of their mucus is much more specific for certain bacteria. See Ravi, V., et al., Antibacterial activity of the mucus of mudskipper Boleophthalmus boddarti (Pallas, 1770) from Vellar Estuary, AES Bioflux 2(1):11–14, 2010. Return to text.
- Lee, H.J., et al., Burrow air phase maintenance and respiration by the mudskipper Scartelaos histophorus (Gobiidae: Oxudercinae), J. Exp. Biol. 208(1):169–177, January 2004. Return to text.