Tag Archives: ichthyology

Weekend Parasitology

A friend gave me a few fillets of katsuo (skipjack tuna).  I’m sure he didn’t know about the cestode guest lurking within one of them!  This is the larva of a certain species of platyhelminth, but completely harmless to humans (you can even eat them without any ill effects).  You may also find them in saba (mackerel) and surumeika (flying squid).  The dish tataki made with katsuo, a specialty of Tosa, is specifically done with the purpose of getting rid of these creatures (with fire).  If you are lucky enough to eat katsuo up north (such as I was served in Iwate) the water temperature is too low for the larvae to survive so the locals always eat their katsuo as-is, without the charring.  Incidentally, this particular fillet was shallow-fried in olive oil with salt & pepper and eaten between two slices of toast for breakfast, with no detectable influence of the parasite on the deliciousness of the fish.


Breeze over Kasumigaura


I had no luck on the water yesterday fishing for mabuna Crucian carp – aside from losing a very good fish that threw the hook at the surface, she had at least a shaku on her (30.3cm).  The wind was too strong for orthodox fishing: a stiff northerly breeze in the morning that only got stronger as the day went on, till it was howling at midday.  We packed up and left the lake at 1:30pm when the wind grew so strong as to lift one’s tackle out the water and send it streaming in a horizontal pennant in the air from the end of the rod.  I think we were one or two days too early or late as the majority of fish in the area were spawning in the shallows, you can hear and see them thrashing about, and such fish do not take the bait.  Some other fish, no doubt spent after their frenzied exertions, were idly sunning themselves at the surface or taking gulps of air and at one spot, where two rivulets conjoined, some fish were leaping out of the water.  The lucky ones would fall down the bank and roll back into the water; one unlucky fish we came upon was stranded and had its eyes and intestines picked out and eaten by the inevitable crows.  Kasumigaura is always an interesting place to visit, and for me a lack of fish in the bag is no cause for disappointment.  I passed some time watching a local man in the shallows with a home-made fishgig, standing as still as a hunting heron, looking to spear passing koi carp – in these days of opulent luxury carp is no longer a staple food in Japan but the older locals still take them.  I also spotted a number of big birds of prey soaring about but had forgotten my spyglass so I couldn’t identify them, but most sensible birdlife was taking shelter from the wind.  On the way back my fishing buddy almost ran over a cock pheasant that had walked blindly into the road, which would have been an ironic end to such a huge fine creature that had survived the Kasumigaura hunting season; luckily the bird came to his senses and ran off just before we flattened him.

Reflexions on mabuna

Looking at the two specimens I caught yesterday, both were middling-large sized and both appeared to be gravid.  In fact, at this time of the year the fish are spawning, and migrate to the shallows to spawn in reed banks that line lakes and rivers; they even migrate into the little channels and man-made canals that feed rice paddies and lotus root fields.  If you catch a mabuna that has reached sexual maturity and is in good physical condition at this time of year, it will almost certainly be gravid, and in fact you will never catch a male mabuna, not in a lifetime of fishing for them.  All mabuna are female.  Just casually looking up “mabuna” online to find out its scientific name – generally Carassius auratus langsdorfii, or just Carassius langsdorfii – I came across this unusual habit.  I had read about the switching of sexes that some fish display – generally all born female then males develop from these in the right numbers for spawning – I think the grouper and certain bass do this, but never the female-only trait.

C. langsdorfii ‘spawn’ generally at the same time (around April-May) as a number of related species: koi carp, the so-called kinbuna (C. buergeri) and nigorobuna (C. buergeri grandoculis) and others, in the same habitat, usually overgrown freshwater shallows.  These types of fish  spawn in the multiple-male-multiple-female “orgy” method common to many fish species (and certain humans, if the internet is to be believed), and during this process the entirely female race of mabuna join in, for their eggs require a sperm of a related species to activate, but fertilisation – and perfectly normal development – takes place without the sperm nucleus ever fusing with that of the egg.  This is not true parthenogenesis since a male sex partner is required, and so is termed instead gynogenesis.  Interestingly the mabuna is polyploid, usually tri- or tetraploid, and so its eggs never require chromosomes from what would usually come from the male gamete.  It also means that mabuna are all genetic clones.  However mabuna are found all over Honshu, and genomic analysis has shown that different water-systems in different locations, such as Biwako or the Kasumigaura lakes, hold different clones.  In fact the classification of funa-type species is extremely difficult, and identification – without post mortem dissection – very tricky; I still have trouble sometimes telling the difference between a herabuna and mabuna, or kinbuna (koi carp are easy to distinguish, as they have barbels).  There also appears to be a certain apocryphal cross-breeding of funa species, leading to fish that anglers refer to as ai-bera or hanbera, and that in some seasons the mabuna seem to have different physical characteristics, although how this is possible is not known and it has never been tested in a laboratory.  How Linnaeus would tear his hair (or powdered wig) after a season of mabuna fishing!

There are several apparent biological paradoxes regarding this species.  The first is that even with a little variation caused by natural mutation, a clone race would be very susceptible to a single pathogen or food shortage, yet mabuna are numerous and have not been affected by serious epidemics that I know of.  Second, if a kinbuna or nigorobuna sperm is required for mabuna eggs to ‘fertilise’, by definition that particular kin/nigorobuna sperm would not fertilise its intended target egg, and a small imbalance in either male kin/nigorobuna or female mabuna numbers would soon be amplified so that one or other would become numerically dominant, leading to the at least local extinction of the other; yet funa species co-exist in a balanced nature in all habitats they can be found in.  There is also the question of evolution, as how such a species developed in the first place, and the various old anglers’ tales of the cross-breeds that are alleged to exist.  The very definition of a species by classical taxonomy is challenged by mabuna.  Who would have thought such simple fishing could be so intriguing?

English names of Japanese Fish

I often wonder how many species I have caught in my time fishing here in Japan; after nearly five years now I think I can name almost any fish pulled out of Tokyo Bay, and identify fish caught in most other parts of Japan too (although Okinawan fish remain a mystery to me). Anyway, over the last few months I finally got round to listing all the fish, and looking up their English names.  In this day and age of internet and instant gratification you can easily find any of these, so to save time I have listed the names only in their respective languages, therefore you need at least a knowledge of katakana and a browser that supports Japanese text to read this list.

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