he attractively marked catfish in the drawing below is Synodontis
njassae, and is the larger and better known of the two
Lake Malawi catfishes belonging to the family Mochokidae (the
other is Chiloglanis neumanni).
lecotype, 192mm, Langenburg, lac Nyassa (Inst Spez,. Zool
Mus. Berlin No. 18191) (From Poll 1971)
S. njassae is endemic to Lake Malawi, where it is abundant
on rocky shores (but it is by no means restricted to this habitat;
see below). It also occurs in the inflowing streams. This Synodontis
is a good addition to an aquarium of Malawi fishes. Notes
on its aquarium care, and photos of an individual with many
small spots, are available in an article by Frank Panis at the
Its colour pattern is quite variable,
with some individuals having many small spots, and others having
only a few large spots. I collected about 500 specimens during
rotenone sampling of rocky shores in 1980, and observed that
the spotting variation appeared to be continuous, rather than
falling into discrete "large spotted" and "small
spotted" forms as many aquarists believe. Specimens with
small, medium, and large spots are shown in a black-and-white
Recently, Snoeks (2004b), without documentation,
listed a "Synodontis sp. 2" from Lake Malawi,
noting "it is my impression that there is at least one
other Synodontis species in the lake." Snoeks
did not divulge if his suspicion is based on color pattern,
ecology, or something else. Until this hypothetical second species
can be substantiated, I continue to regard S. njassae
as a single variable species.
has a strong, sharp, serrated spine at the front of the dorsal
fin and each pectoral fin. These spines can be locked at right
angles to the body. The fish can also produce defensive squeaking
sounds, which are easily audible through an aquarium glass,
using its pectoral stridulation mechanism. The mucus covering
the spines is apparently toxic. While netting stunned individuals
during rotenone sampling, I was nicked on the thumb by the tip
of a spine. Within a few seconds, the skin around the nick swelled
into a tight, painful, almost hemispherical lump that took a
couple of days to disappear; a small scar remains at the site
of the puncture over 30 years later.
Specimens of Synodontis
njassae with small, medium, and large spots,
collected by Geoffrey Fryer in the vicinity of Nkhata
Bay and sent to the British Museum (Natural History)
in 1957. Photo
© M. K. Oliver
Because of these fin spines and its large, bony head, S.
njassae (known to the indigenous fishermen as Kolokolo
or Njekayeka, both words that probably imitate the squeaking
sound the fish makes as just described above, and to Europeans
as the Squeaker) is not an important food fish. It is, however,
eaten when available. Some fishermen actually bite off the spines
to make the fish safe to handle (see photo below left, by M.
off the spines to make the fish safe to handle.
The vertical distribution of S. njassae was studied
by Thompson, Allison, & Ngatunga (1996a). They sampled offshore
fishes at six locations using mid-water trawl and gillnets.
I had the impression that this catfish is confined to rocky
shores in relatively shallow water. Wrong! Thompson et al. demonstrated
that, in fact, it is also abundant in the pelagic zone (in open
water, well above the substrate). By day it occurs all the way
down to the limits of dissolved oxygen — 230 meters (750
feet), moving up to the surface layers at night. In the southwest
arm of Lake Malawi, S. njassae is common at all depths
but most abundant in deeper water, constituting (by weight)
a mean of 2.0% of the catch of demersal fishes at a depth of
10 m (33 feet), 4.5% at 30 m (98 feet), 3.6% at 50 m (164 feet),
2.8% at 75 m (246 feet), 7.6% at 100 m (330 feet), and 8.5%
at 125 m (410 feet) (Duponchelle et al., 2000a).
Most individuals captured in open water have a standard length
(SL, without caudal fin) of 90 to 110 mm (3½-4.3 inches),
but some as small as 50 mm (2 inches) or as large as 200 mm
(8 inches) SL were caught. This species attains a maximum length
of 30 cm (11.8 inches) (Eccles, 1992).
Allison, Irvine, Thompson, & Ngatunga (1996) reported on
the diets and food consumption rates of some common offshore
pelagic fishes, including S. njassae. This catfish
(again, to my surprise) feeds extensively on zooplankton, all
day long but more intensively during the night when it is nearer
the surface. The predominant food items found in 150 stomachs
of S. njassae from open water included the planktonic
crustaceans Tropodiaptomus cunningtoni and Mesocyclops
a. aequatorialis and the lakefly Chaoborus edulis
(fourth instar larvae, adults, and pupae); less frequent food
items included planktonic algae (mainly Aulacoseira), other
planktonic crustaceans, other insects, and detritus (Allison,
Thompson, Ngatunga, & Irvine, 1995, table 9.9).
Thompson, Allison, Ngatunga, & Bulirani (1995) summarized
what is known of the breeding biology of Synodontis njassae.
The breeding site within the lake remains unknown. The eggs
are tiny (0.16 mg per egg); fecundity is high, with a mean of
1341 eggs per fish (817 females examined). Although some females
up to 14 cm (5½ inches) in length were immature, the
average size at first maturity was estimated to be 11 cm (4.3
inches) and some females matured at 10 cm (4 inches). In ripe
females, the ovaries can attain 8-9% of body weight. The authors
found females ready to spawn throughout the year; no seasonality
was observed. No larvae or juveniles were found offshore; individuals
less than 10 cm (4 inches) in length were rare in the open-water
One of the puzzles of speciation in the
African rift lakes is why Lake Malawi has only this one Synodontis,
while Lake Tanganyika, with a smaller cichlid flock, has evolved
a flock of at least 7 endemic species of Synodontis (plus
two more widely distributed species).
Photograph © 1998
by K. Armke, from Armke's Rare Aquarium Fish. Used
with the kind permission of Ken Armke.