That Fish Blog – Aquarium Advice and Information

Octopuses have much going for and against them as pets. They are, without a doubt, the most intelligent of the invertebrates, and often seem to rival much more “advanced” creatures in brain power. Able to distinguish and associate various shapes with a food reward, some have even learned to unscrew glass jars to obtain food. In one laboratory, cameras revealed that an octopus was leaving its aquarium each night to prey upon crabs held in a neighboring tank. Each morning, the octopus was found back in his own aquarium, having crossed several feet of dry shelf space in his nocturnal travels! One that I kept would, according to my grandmother, “watch her” as she prepared dinner (octopus see very well, and notice movement outside their aquariums). Unnerved by the thought of our pet witnessing the demise of his relatives, she would cover the aquarium with a towel on those days when she cooked octopus or squid for dinner!

On the down side, however, all species studied are quite short-lived (2 years at most) – quite odd considering their complex lifestyles. Males generally expire right after mating, and females survive only long enough to see their eggs through hatching.

The species most often seen in the pet trade is the common tropical octopus, Octopus cyaneus (please note that there is a good deal of confusion as to the identification of this species). Growing to a maximum length of 12 inches, it does well if provided excellent water quality (manage it as you would a delicate reef fish) and a secure retreat in which to hide. Octopuses absolutely need to hide and are intolerant of disturbance (although once acclimated many will become quite bold at feeding time). It is also important to avoid suddenly putting on a light if the room in which the aquarium sits is dark. When disturbed, octopuses release a dark-colored ink (sepia), which can be toxic to the animal in close quarters.

Bear in mind that octopuses consume large amounts of food and produce copious waste products – good filtration, frequent water quality tests and water changes are vital if you are to keep them successfully. Give your octopus the largest aquarium possible (this will help with water quality and in reducing stress on the animal) and be sure the lid is weighed down or otherwise fastened. The common tropical octopus does well at temperatures of 76-78 F. As most species are nocturnal, you should equip the aquarium with a bulb designed for nighttime viewing so as to be able to observe your pet without disturbing it.

Most octopus favor crabs, shrimp, clams, scallops, mussels and other shellfish, but usually take fish as well. Seafood markets are useful sources of food for your pet – as we know little of their nutritional requirements, I suggest providing as much dietary variety as possible. The wide range of frozen marine foods now available will provide you with a great many options as well.

Other species sometimes offered for sale include the red or pygmy octopus, O. bocki, which is highly nocturnal, and the common octopus, O. vulgaris. As the common octopus occupies a range spanning the Mediterranean, the Sea of Japan and the Eastern Atlantic, it is likely a fairly hardy creature. However, with a leg-span approaching 3 feet, it is too large for most home aquariums.

It is important to remember that all octopuses, even very small ones, can inflict painful bites with their sharp, parrot-like beaks, and that they can never be considered “tame” enough to handle. Most if not all produce venom in order to subdue their prey, and even venoms not shown to be dangerous to people can cause severe or even fatal reactions in particularly sensitive individuals. Amazingly, the tiny the blue-ringed octopus, Hapalochlaena maculosa, quite capable of killing a human with one bite, is sometimes offered for sale. Learn to recognize this species and avoid it at all costs.

Breeding octopuses in captivity is difficult, as is raising the young. Recent research at the Spanish Institute of Oceanography indicated that dietary factors, especially the absence of fatty acids such as DHA and EPA, are responsible for high mortalities among those that do hatch in aquariums. Enriched brine shrimp have been used with some success, but more variety is likely needed. I would experiment with various species of marine shrimp, worms, plankton and tiny marine creatures seined from eel grass beds and other marine habitats (check the legality of collecting before doing so).

Octopus husbandry is in need of much attention by serious hobbyists. These fascinating, complex creatures are impacted by habitat loss and collection for the food, bait and pet trade. Breeding them in captivity will certainly take pressure off wild populations and help in understanding what they need to survive in the wild.

Please write in with your own thoughts and questions. Thanks…until next time, Frank.

You can see photos of hatchling octopuses and read about a captive breeding effort at:http://www.bbc.co.uk/norfolk/your/a-z_norfolk/a-z_octopus.shtml

Please welcome back Frank Indiviglio with another interesting article.

Studying fish behavior is both a fascinating and very practical endeavor for the fish keeper. In addition to opening one’s eyes to the amazing diversity of fish lifestyles and behavioral adaptations, research concerning your pets’ natural behaviors will also lead to much greater success in keeping and breeding them.

The primary motivation behind animal behavior is survival – breeding, finding a suitable environment, obtaining food and avoiding predators (yes, human behavior often seems to break this rule!). Of course, even the best-designed aquarium is a poor mimic of nature, and so captive fishes must modify their behaviors – sometimes so much so that the actual purpose or function of what the fishes are doing will be lost on us. However, with experience, you should be able to see the relationship that the captive behavior has to its natural counterpart.

A wonderful aspect of the study of fish behavior is that it will provide a lifetime of surprises – there is far too much for any one person to know, and new facts emerge, quite literally, on a daily basis. With careful observation and research, you may well be able to discover something new. Today I will focus on just one facet of behavior – the time at which fishes are active, and how this affects their welfare in the aquarium.

When selecting fishes for your aquarium, it is important to consider whether they are diurnal (active by day), nocturnal (active by night) or crepuscular (active in the dim light of evening and early morning). This will affect both your enjoyment of your pets and the composition of species that you might wish to include in the aquarium.

Nocturnal fishes such as the fire eel, Mastacembelus eyrthrotaenia, and other freshwater eels, need a place to hide during the daytime. If denied this, they may become stressed and will languish in captivity. However, eels, catfishes and other species that barely move by day change radically at night, and may engage in a surprising degree of activity. These nighttime wanderings may disturb diurnal fishes and prevent them from resting properly, thereby impairing their health.

Unlike the always “ready-to eat” oscar, Astronotus ocellatus, and other Cichlids, nocturnal fishes often appear placid by day and morph into quite aggressive predators only as night falls. For example, octopuses, snowflake moray eels, Echidna nebulous, and similar species are usually quite content to spend the day secluded in a favorite retreat – easily tricking the novice into believing that they are compatible with their tank-mates. At nighttime, however, they undergo quite a change, and will quickly devour smaller neighbors.

Many diurnal fishes, such as the princess parrot fish, Scarus taeniopterus, and related species, swim about actively in daylight but secrete themselves within caves at night. Again, if you see them only during the day, you may miss such points and fail to provide for their needs (shelter-sleeping species become stressed if forced to remain in the open at night).

Please bear in mind also that many nocturnal fishes will not feed during the day. Some, including most catfishes and moray eels, will forego their nocturnal habits once they adjust to captivity. Many, however, (i.e. the fossil catfish, Heteropneustes fossilis) remain strictly nocturnal even after years in captivity, and must be fed at night if they are to thrive.

Just as nocturnal species may unsettle diurnal fishes at night, actively swimming fish (by day or night) may stress species that are largely sessile (fish which move about only occasionally). Most typical “sit and wait predators,” such as the various anglerfishes, will be greatly disturbed if forced to remain in close proximity to vigorous, mobile species (also, bottom-feeding predators usually do not obtain enough food when kept with surface-feeding fishes).

The best way to observe nocturnal fishes, and to see how diurnal fishes behave at night, is by utilizing a bulb designed specifically for nighttime aquarium viewing. Be sure to invest in such bulbs, as they will open up an entirely new world of fascinating observations and learning opportunities for you. If you plan to focus on nocturnal fishes, you may wish to consider a complete reverse light cycle, in the manner of zoo exhibits for nocturnal creatures. If a dimly lit room is available, you can leave the night-viewing bulbs on during the day, and give the fishes their “daytime” at night. This may give you more time to observe your nocturnal fishes – unless, of course, you are yourself “nocturnal”! I have been able to learn a great deal about a number of animals, both at home and while working at zoos, in this manner. Be sure to research your fishes’ natural history so that you can provide a day/night cycle of the proper length.

I’ll explore other aspects of fish behavior in future articles – until then, please write in with your observations and questions. Thanks, Frank.

An interesting article concerning the effect of light on fish activity is posted at:http://www2.hawaii.edu/~delbeek/delb12.html

Thanks Frank,

Until Next Time,

Dave

Mudskippers, the largest species of which reach a length of 12 inches, inhabit tidal flats, river mouths and mangrove swamps in East Africa, Southeast Asia, Australia, and along the Red Sea.

Gill covers tightly seal the gill chambers, and water stored there keeps the gills moist and provides oxygen to the fish as it scuttles about on land. Mudskippers also absorb moisture from the damp mud upon which they usually travel when out of water. Although it is tempting to think of mudskippers as representing an early stage in the development of amphibians, the creature that gave rise to frogs and salamanders was more like the Australian lungfish, Neoceratodus fosteri, in appearance and in its method of breathing (utilizing primitive lungs).

The most commonly available mudskipper in the pet trade is Periopthalmus barbarus, a fairly hardy species that reaches a length of 6 inches. Like all mudskippers, it hails from brackish water areas.

Mudskippers are fairly tolerant in their salinity requirements, and will do well under typical brackish water aquarium conditions (salinity of 1.005-1.015) and temperatures of 75 – 80F. They require a “beach” area, which can be a separate, drainable plastic container within the main aquarium or designed as small islands fashioned from non-toxic tree roots, coral heads and rocks. The popular “aqua-terrariums” now on the market make excellent mudskipper homes as well. Remember to keep the water shallow, or to provide easy access to land, as they are poor swimmers (not something you usually worry about when keeping fish!).

Most mudskippers do well in captivity if provided with a suitable habitat. Males, however – distinguished by their large dorsal fins and bright colors – are very territorial, and dominant specimens will make life miserable for others, so plan your group and space accordingly.

Although they prey upon live invertebrates such as crabs and insects in the wild, mudskippers adjust well to frozen foods such as prawn and clams. I also provide a vegetable-based frozen food from time to time, and find they accept this readily as well. Their food should be placed on land, as most species will not feed while submerged. Mudskippers are especially fond of live crickets, small shrimp and other such foods, and these should form a large portion of their diet. Their acrobatics when chasing live food – they often flip over in their excitement – never fail to delight me.

Brackish water community tanks containing mudskippers and fiddler crabs make fascinating exhibits. The interactions between the crabs and mudskippers (assuming they are properly matched in size!) go on all day long. If you establish a deep water area (mudskippers will do okay as long as they can exit the water easily) you can add such fascinating fishes as four-eyed fish, Anableps spp., scats, Scatophagus argus and rubrifus, monos, Monodactylus argenteus, and, of course, the amazing archer fish, Toxotes chatareus. In fact, archer fish are at their best in an aquarium containing a land area because in such they can show off their incredible ability to knock crickets from land into water. Somehow compensating for the refraction of light through water, archerfish eject streams of water at insects (best observed by placing crickets on branches positioned over the water’s surface), hitting them unerringly and thus securing a meal. They will also aim water at your eye movements, so be careful!
I’ll cover the creation of such aquariums in future articles. Until then, please share your observations and write in with your questions. Thanks, Frank.

For more information on establishing aquariums for brackish water fish, please see the article Brackish Water Basics, posted on on February 26, 2008:

They are also amazingly adept at locating food – a school I kept at the Prospect Park Zoo in NYC hit food dropped on the water’s surface as quickly as do most sighted fish. In fact, blind cave fish do quite well in aquariums housing other fish species.

Recently (January, 2008) it was discovered that young blind cave fish can detect light via unique compounds in the brain’s pineal gland (the embryos begin to develop eyes, but these degenerate rapidly). This ability declines with age.

In contrast to most cave-adapted fish – which require cold, hard water if they are to thrive – blind cave fish are quite undemanding pets. In fact, they do best at 78-82 F, as their native waters are quite warm. If kept alone, slightly hard water should be provided, but they adapt easily to conditions suited to most community-type tropical fish. Despite a very specific natural diet (see above), blind cave fish remain healthy on almost any commercial fish food – I have successfully used a mix of omnivore flakes and pellets, along with frozen foods. They ravenously devour black worms, brine shrimp and such, and are especially fond of crushed crickets and other insects. Their reaction to insect food brings, at least to my mind, an image of feeding behavior in their native cave. At feeding time, they compete quite well with other fish and rarely require special attention.

Blind cave fish are placed within the order Charachiformes, an extremely diverse group of fishes containing well over 1,500 species, including tetras and the infamous piranha. I will write about piranhas in a future article, and will include photos of some that became “attached” to me while I was seining for knife fish in northern South America. Until then, please forward your comments and questions. Thank you. Until next time, Frank.

A fascinating account of the first expedition to collect blind cave fishes, including original drawings and photos, is given in Zoo Expeditions, by William Bridges (William Morrow & Co., 1945). Long out of print, this book is well worth searching for.

An interesting article on the evolution of eye regression in this fish is posted at:
http://findarticles.com/p/articles/mi_qa3746/is_199809/ai_n8816250

The blind cave fish is found in only one cave, La Cueva Chica (the “Little Cave” – the entrance is only 15 feet wide) near Pujal, in San Lois Potosi, Mexico (related species have since been found in other caves). This fact alone should grant it special status among fish keepers, but there is much more to distinguish it – including a rare glimpse at fish adaptation in progress. Apparently, fish with normally developed eyes live in a nearby river, the Rio Tampaon, and are regularly swept into the cave by the current. There, deprived of light and the need for sight, the eyes degenerate. As time goes on, their descendents are born with gradually more reduced eyes, until the eyeless form emerges. Although I have not read evidence of it, I imagine that inter-breeding with eyeless fish already in the cave may hasten the process.

Fish in pools nearest the cave’s entrance rely upon flies, spiders and other invertebrates for food, while those deep inside subsist upon bat guano, dead bats and, I would venture a guess, fleas and other invertebrates that fall from the bats’ fur.