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Nothos - names, aggression and sex ratios
It would appear that a contribution I made earlier was accidentally
truncated from the digest edition of KillieTalk V2 #270 so I will
copy it below for the benefit of those who did not receive it:
Julian Haffegee wrote......
>
>Subject: notho naming questions
>
>>>
>>>> * Nothobranchius albimarginatus Watters, Wildekamp & Cooper,
1998
>>>> * Nothobranchius annectens Watters, Wildekamp & Cooper, 1998
>>>> Deutsche Killifisch Gemeinschaft Journal, 30 (3): 52-63.
>>>
>Who named these fish? (Do the names and
>date above refer to the collecter or namer).
>
The describers and authors of the article named the fish (this is
usually the case). In this instance, the authors also happen to be
the collectors of the type specimens (which is not always the case).
>
>Do annectens and albimarginatus have literal
>meanings (white edges?).
>
The etymology relating to these species names is as follows:
N. annectens - From the Latin annectere = to connect; in reference to
the position of this species forming a link between N. guentheri on
the island of Zanzibar and the other species of the N. guentheri
group living on the mainland. An adjective. This represents the
mainland species of the group that is probably most closely related
to N. guentheri itself (in our opinion, that is).
N. albimarginatus - From the Latin words albus = white, and marginis
= margin; in reference to the color pattern of the males (distinctive
white margins to the dorsal and anal fins). An adjective.
>
>What techniques did they/you use to decide
>that these fish were their own species and
>not too similar to something else?
>
By studying the characteristics of the wild specimens (e.g.
meristics, morphology, color pattern, behavior, geographic
distribution, etc.) and the comparison of such characteristics to
those of other Notho species, especially those that were deemed to be
closely related.
>
>Is the article in DKG journal in German , if so
>does it get published elsewhere in a few months?
>
Yes, the article is in German, as all articles in the DKG Journal
are. The article does not have to be published elsewhere in a
different language for the descriptions to be valid, if that is what
you are asking. However, in this case we are preparing an English
version that will, in due course, be offered for publication in
another journal, although that may take some time.
Chris Graseck wrote.....
>Subject: More questions about Nothos.
>
>........My biggest concern at this point is aggression.
>Is N. rachovii a particularly aggressive fish?
>
Relatively speaking, N. rachovii is not as aggressive as many other
Nothos but they certainly can be aggressive to the point where the
females can suffer fatal damage.
ALL Nothos are aggressive but to different degrees depending on the
species and often also on individual specimens. Some males can be
real rogues and destroy females in short order, while others, of the
same species, can be relatively well behaved. You just have to be
aware of this, watch the fish very carefully and separate them when
necessary. And, of course, anyone who has kept wild Nothos will know
that they generally tend to be far more aggressive than tank-raised
specimens of the same species.
The best way to deal with aggression in most Nothos is to raise and
breed them in groups (e.g. 5-6 males and 10-12 females) and do not at
any time separate them. (For example, if you take one male out and
keep him on his own for a week or two and then put him back with the
rest I guarantee you will have problems). Raise them together as fry
and as they grow and mature remove those that you don't need or want
until all you have left in the tank is your select breeding group.
That is not to say there will not be any fighting in the group but
they do get used to each other if raised together. Also, with a group
the aggression is spread around (although the less dominant males and
the smaller females will still be picked on) and the sparring between
the males will draw their attention away from the females to some
extent. This doesn't work with all Nothos (e.g. it won't with N.
ocellatus) but it is the method that I try to use whenever possible.
Another obvious advantage is a larger gene pool. Of course, it does
mean that larger tanks will be needed (I use a lot of 10 and 15
gallon tanks for such groups).
Incidentally, if I have limited numbers of females, I commonly use a
reverse ratio of males to females and having a relatively larger
number of males does not mean that the females will be beaten up any
more than usual. In fact, it often has the opposite effect because
the males are so busy scrapping with each other that the don't pay as
much attention to the females. I have a number of tanks where that
situation prevails at present. For example in each of two of these
cases I have about 4 females to about 12 males.
>
>Can a pair or trio be kept in a 5 gallon aquarium.
>
Yes, certainly, but watch the females carefully for signs of damage.
-------------------------------
Now, in response to a couple of issues raised in that part of
KillieTalk V2 #270 that I did receive...........
Lee harper wrote.......
>Subject: Re: KillieTalk Digest V2 #269 (N. foerschi)
>The only problem I have had with N. foerschi is that
>the males tend to outnumber the females by at
>least 20:1 at maturity. I don't know yet if this is survival
>of the fittest or if that is a skewed hatch ratio. I am now
>running an experiment with several hundred fry where
>I remove any male as soon as it shows color. I am
>now into about the 4th week of doing this and they
>still keep coloring up. I have identified a few real females
>and removed them for next generation breeding stock.
>I have not kept track of how many males (and I can not
>go back and count them - many of them are no longer
>with us). If I end up with 20 females, I still have about
>20 males saved for them. In retrospect, I should have
>kept records. Next time, maybe. They are prolific,
>no doubt. Other Nothos have not been so skewed
>in my experience, but also not as prolific.
In general, I tend to hatch more males than females with most species
of Nothos but no more so with N. foerschi than any other species, and
certainly not with the highly skewed sex ratios Lee is experiencing.
I would think this is not a general tendency with this
species and the conditions in his fish-room must be influencing this.
The reasons for skewed sex ratios in Nothos has been debated
extensively but I have yet to read or hear of a convincing
explanation that can also be supported by controlled experimental
studies.
I personally don't think that factors such as pH and temperature, ON
THEIR OWN, are the primary causes. In discussions I have had with
biologists at my university about this, it would appear that it is
most likely the conditions the adult breeders are subjected to is
what determines the sex ratio of their off-spring.
Although I cannot presently provide experimental evidence for this,
my feeling is that it is the overall environmental conditions that
the adults are subjected to that determines the sex ratio of any
particular batch of their off-spring. Environmental conditions that
are essentially adverse and place the population under stress would
tend to favor more males and fewer females (I think so, anyway). If
the habitat conditions are such that the population density cannot be
adequately supported then a natural adjustment would be made by
lowering the number of "egg producers" (the females) in the next
generation.
Adverse environmental conditions could include, for example, a very
high population density and inadequate food supply. Inadequate rains
and/or rapid drying of the habitats could cause overpopulation and
under such conditions the water may well also have an unusually low
pH and/or a high temperature, but these would be secondary factors
only that may or may not accompany the principal cause of the stress
on the population which, in this example, is overpopulation.
I would further suggest that in our fish-rooms we maintain Nothos
under conditions that would invariably place the "population" under
stress and perhaps that is the fundamental reason for sex ratios that
are almost invariably skewed towards a high proportion of males. For
example, compared with the natural situation, we always overcrowd our
tanks (this is unavoidable) and the constant fighting among males and
the incessant driving of the females simply does not happen in nature
where there is plenty of space, hiding places for the females, and
very turbid water that must surely make it easier for the fish to
escape
the constant attention of others. We think that by placing a trio in
a 5 gallon tank or a dozen or so fish in a 15 gallon tank, that we
are providing them with plenty of space but, compared to conditions
in their natural habitats, this is most often not the case. Even when
we maintain just a few pairs of Nothos in a large tank there will
always be split fins and other damage in evidence; in contrast, wild
fish almost never show this sort of damage.
Anyway, this is merely my view on the subject but I also think that
if anyone wants to conduct controlled experiments in an attempt to
learn more about the causes of skewed sex ratios in killies then
considering environmental stress as a primary causative factor could
be a rewarding approach to the problem.
Barry Cooper wrote......
>
>I don't find N. rachovii too aggressive, usually. I will
>say that the wild N. rachovii Beira '98 are more
>aggressive and drive the females pretty hard. A trio
>in a 5 gal should be perfect. As one always should,
>keep an eye on the females for damage caused by
>an overly amorous male.
>
With regard to the wild N. rachovii Beira '98 and as a further
example of what I wrote about the advantages of group spawning Nothos
I can relate the following:
I have two spawning setups for my wild N. rachovii Beira '98. One
consists of a group of 6 males and about 20 females in a 15 gallon
tank. The males scrap a bit but not seriously so and there is just
the odd split fin among them. The females are in perfect condition
and do not get beaten up by the males at all. The second setup
consists of a single male (a particularly magnificent specimen) with
3 females in a 3.5 gallon tank. These 3 females are in a constantly
battered condition and, in fact, every week or so I have switch them
with "fresh" individuals from the 15 gallon setup (to give them a
chance to recuperate and
regrow their fins).
__________________________________________________
Brian R. Watters
University of Regina
Regina, Saskatchewan S4S 0A2, Canada
Ph: (306) 584-9161 (home); (306) 585-4663 (work)
Fax: (306) 585-5433
E-mail: bwatters at sk_sympatico.ca