Compulsive Hoarding

A disorder with ancient roots?

I think we all know some people who are ever so ready to throw away something they no longer fancy or to discard some item if a newer version is available. But we may also know people, who behave in exactly the opposite way: they never throw away anything but keep and store and guard even things that no longer seem useful. That kind of behaviour can be compared to what is termed “hoarding” and, if compulsive, it is now considered a mental disorder of the “obsessive-compulsive” nature. But is it an atavism, a re-surfacing of an ancient trait with roots in the animal kingdom as suggested by Sandro René Pinto de Sousa Miguel, Rodrigo Ligabue-Braun of Porto Alegre in Brazil, akin to narcolepsy and quadripedalism in humans, which have also been linked to atavisms?

Hoarding, especially of food but occasionally also of material or other items, is certainly common in the animal kingdom and helps individuals survive lean periods. And immediately La Fontaine’s famous poem “La cigale et al fourmi” that I had to learn as a pupil during my High School French lesson, comes to mind. Indeed, there are several examples of invertebrates that store or cache food or, in the case of leaf cutter ants, even collect and tend inedible leaves to grow on them edible fungi. Honey bees are so successful (unlike the equally social hornets) and survive the winter, because they prepare and store food for the cold season. Although not usually overwintering, spiders, too, can often be seen in summer to keep numerous wrapped-up insect prey in their orb-webs for later use.

More obvious hoarders are found amongst our feathered friends and some of them behave seemingly intelligently when they attempt to hide food items and then firstly look around to make sure no other bird observes where they hide their treasures. A behaviour such as this has been reported from Corvus corax ravens by the Austrian researchers T. Bugnyar and K. Kotrschal and also the Eurasian jay Garrulus glandarius by the Cambridge University scientists E.W. Legg and N.S. Clayton. North American woodpeckers are less selfish and establish food stores that are accessible to other wood peckers, but whether shrikes like Lanius collurio allow other shrikes to access the insects, and even small mice and lizards, they store on thorns in the open, I do not know. However, policing food stores such as these, which are visible and in the open would be quite a task. Besides, hoarders with multiple caches (to reduce pilferage) run the risk of forgetting some of their troves, and in the case of forgotten and buried seeds, help spreading trees. A special facet of hoarding is that, which is represented by the New Caledonian crow Corvus moneduloides that bends twigs into hooks to extract grubs from wooden trunks with and then hides and hoards these precious tools.

Proverbial hoarders are the hamsters. It has been reported that European hamsters of the species Cricetus cricetus may have many kg of grain (up to 60 kg !) in their nests  – and it’s all for themselves (and their offspring). Packrats and squirrels, too, are well known hoarders and beavers establish food stores that can be used by anyone of their family. Some of the best-studied mammalian hoarders are shrews, especially a species by the name of Blarina brevicauda from the northeastern region of North America. To survive the winter they collect and cache food items in their burrows that can contain seeds and dry fruit, invertebrates and even small mice. It was this species of shrew that the Brazilian researchers, mentioned above, compared obsessive human hoarding with to suggest that the latter was an atavism going back to ancient evolutionary roots. The problem is, human hoarders more often than once, not just hoard food, but inedibles like coins, stamps, toys, clothes, buttons etc., and some are even known to hoard and guard some really weird and useless things like used underwear, smelly socks, cigarette buds, etc. Do animals do that also? Well, in the Statistical Manual of Mental Disorders, 5th edition (DSM-5) such behaviours in humans are now classified as a mental disorder. Maybe it’s risky then to mention I collect coins with animals on them.

© Dr V.B. Meyer-Rochow and, 2021. Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to V.B Meyer-Rochow and with appropriate and specific direction to the original content.

Giant Fishes of the Rivers

How much longer will we have them?

The vertebrate class of Pisces contains members of two major groups of fishes: the cartilaginous species and the bony fishes. The most massive (if not the longest as well) of all fish are the Whale Shark (Rhincodon typus) and the Basking Shark (Cetorhinus maximus). These two species are peaceful giants, feeding on plankton that they filter out of the ocean water with their comb-like gill rakers. However, in this blog I want to write about giant freshwater and not marine fish. Yes, river fish, for several of them are bigger than the marine bony species (with one exception: the oarfish Regalecus glesne, of which during the 1967 “Walther Herwig” South Atlantic Expedition I caught a glimpse of one 7.30 m long specimen. This midwater species is said to reach a maximal length of 13 m).

What prompted me to write this blog was the sad news that the giant Yangtze River paddlefish Psephurus gladius was officially declared extinct. It thus follows the Yangtze freshwater dolphin Lipotes vexillifer, affectionately called ‘the baiji’ in Chinese but declared extinct in 2006. In 1970 there were still 25 tons of Yangtze paddlefish caught, but the last individual was probably killed in 2007. Specimens of at least 5 m in length existed. Another Chinese giant with a length of approx. 4 m is the Chinese sturgeon Acipenser sinensis, but it may also soon be gone forever for its population decreased by 98% from 1973-2010. As of this year (2021) all commercial fishing in the Yangtze will be banned for 10 years, but as welcome a measure as this is, it cannot bring back what is lost forever.

Probably the largest with a maximum length of around 7 m of all freshwater giants is the Beluga sturgeon Huso huso of the Caspian Sea and the Sea of Azov. Because of the value of its roe (the famous “Caspian caviar”) it is farmed, but the eggs of its also farmed but only 5.5 m long relative, the Huso dauricus, are considered even tastier. In northern Europe adults of the 3 – 4 m long sturgeon Acipenser sturio used to enter rivers to reach their breeding grounds upstream, but one of the few streams where these sturgeons now still breed is the Gironde in France. Recolonisation efforts are in progress elsewhere, but so far with minimal success. A huge surprise for our professor and us students of the Zoology Class at the University of Kiel in 1968 was when an almost 2 m long catfish of the species Silurus glanis was delivered. It had been caught the day before in the small North German freshwater stream known as the Trave. The East Asian Mekong River Pangasianodon gigas catfish and South American species of river catfish are said to reach maximum lengths of 4 m and can become a danger to bathers. Of the other South American freshwater giants the Arapaima gigas with a reported maximum length of 3.4 m and the electric eel Electrophorus electricus with a length of 2.5 m need to be mentioned.

Africa’s largest freshwater fish is the Nile perch, but it hardly reaches 2 m. On the other hand there are some quite big bony fishes in the North American Mississippi-Missouri river system. There is the North American paddlefish Polyodon spathula and the fierce-looking alligator gar that can both reach a length of 3 m. Although not in imminent danger of becoming extinct, these two species are considered vulnerable and an analysis of what led to the extinction of the Yangtze River paddlefish may help save the North American species and other freshwater fish giants too. It is believed that the biggest threats to the vulnerable freshwater fish giants (but even smaller species as well) are dams that block the fish’s access to upstream spawning grounds, and furthermore overfishing, the use of illegal methods (like electro-fishing, nets with unacceptably small mesh widths, and explosives). Pollution of the river water by chemicals like insecticides, by effluents and other wastes from urban areas, and by fertilizers used in agriculture must not be forgotten. But what is certainly interesting is that rivers compared with the oceanic habitat contained more giant bony fish species than the sea. Any suggestions why?  

lication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to V.B Meyer-Rochow and with appropriate and specific direction to the original content.

© Dr V.B. Meyer-Rochow and, 2021. Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to V.B Meyer-Rochow and with appropriate and specific direction to the original content.

You Don’t See Them, but They Sure Are There

The Ears that Fish Have

That fish can hear was documented nearly 100 years ago by Nobel Prize winner Karl v. Frisch, famous for his work on honeybee communication. Freshwater fish of the carp family, like most bony fishes, not only possess swim bladders that allow them to stay buoyant at different depths, but unlike others also possess small bony connections between the fish’s inner ear and the swim bladder. The gas in the latter gets compressed in response to sound pressure in the water, starts vibrating, and then transmits the signal via the aforementioned small bones, known as Weberian ossicles, to sensitive hair cells of the inner ear. Sound amplitude (loudness) and frequency (pitch) are important, but even in fish with the best hearing, sounds above 6,000 Hz would be ultrasound to them and in swim bladder-lessfish like the fast mackerel and the tuna but even in the more sluggish Antarctic icefishes only lower frequencies can be detected.

Sounds are longitudinally transmitted waves, whose frequencies and amplitudes may vary. Because of the water’s greater density than that of air, sounds are propagated 4.8 times faster in water than in air. In a broad sense sounds are generated by movements or vibrations and in water can be the results of an animal’s vocalizations or activities, of sounds created by ice-floes or logs rubbing or bumping against each other, breaking waves, anthropogenically-produced noise like explosions and disturbances created by ships. In order to sense the sounds, fish use ear stones, i.e. so-called otoliths. Bathed in endolymphatic fluid and resting on a pad of receptor cells with sensory hairs, the two major otoliths are located just below the brain in two bony sacs of the inner ear known as the saccule and the utricle. The otoliths are part of the bony vestibule’s two regions, i.e. the cochlear portion (for hearing) and the vestibular portion with its semicircular canals (for balance and angular change). Thus, otoliths can be said to be involved in the detection of gravity and linear accelerations and serve as a structure of hearing in fish, so well explained in a recent review by Dr. Tanja Schulz-Mirbach of Munich.

Otoliths are hard, durable structures that consist primarily of calcium carbonate (CaCO3) in the form of aragonite.They remain largely unchanged during the digestion in the stomach and gut of a predator. They are thus an excellent structure to estimate a fish’s age, because their size increases by periodically laid down alternating opaque and translucent bands that consist of CaCO3 and collagen fibres. As daily increments are regularly added, researchers can correlate the number of layers with the fish’s body length and use the tabulated data to identify the fish’s age. What makes the study complicated is that the otoliths, not being translucent enough to count the layers, need to be sectioned. Furthermore, although the shapes of the otoliths are species-specific, they can vary in individuals of the same species, depending on the fish’s developmental stage and if the fish was actively swimming or passively drifting.

In Antarctic icefish my Polish colleague Ryszard Traczyk and I have recently concluded that the more spherical otoliths of larval specimens and the longish otolith shapes of the adults are the results of the inertia and friction experienced by the otoliths in their endolymphatic fluid when the fish swim: larvae swim less than adult icefish and the latter swim less than mackerel (which possess the most elongate otoliths). It is entirely possible that oscillations of the dense otoliths generate shearing forces that deflect the sensory hairs of the cells they are resting on, when the oscillations are due to disturbances in the water made by nearby prey or the approach of a predator. Responses to such disturbances in the “acoustico-lateralis” vicinity of the fish would then not only be sensed by the lateral line system, but picked up by the fish’s otoliths too and sent to the brain via the 8th cranial nerve, often referred to as the vestibulocochlear nerve. So, do fish make some noise and can they hear? Actually only a few produce sounds, but all bony fish can hear. However, there’s certainly no need to whisper when you sit in front of your aquarium and watch your colourful aquatic beauties in their 3-dimensional world.

© Dr V.B. Meyer-Rochow and, 2021. Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to V.B Meyer-Rochow and with appropriate and specific direction to the original content.