Nutrition and growth of fry and fingerlings
The pike-perch is a warm water fish with good growth at temperatures of about 26°C (Hilge 1990). Willemsen (1978) observed pike-perch in the effluent area of a power-plant at water temperatures of 3&31 "C. In an experiment with fish of 14 g body weight acclimated to a range of temperatures, no
mortality occurred up to 35T, while the fish stopped feeding
at 32°C. The best growth was obtained at 28-30°C (Willemsen
1978). Obviously good growth in ponds can only be achieved
in regions with long warm weather periods, which do not exist
over the entire range of this species. Hence, different growth
performances may result from either limited temperatures or
by the availability of suitable food items. Thus, mean growth
rates in weight and length of pike-perch in Hungary were
reported to be 50 g per 13 cm, 100 g per 25 cm and 350 g per 32
cm after 1, 2 and 3 years, respectively. Under more favourable
conditions, pike-perch may reach 50&1000 g per 4C50 cm in
3 years (Tolg and Penzis 1966). In the central regions of Russia
one-summer-old pike-perch may have an average weight of 25-
30 g, whereas in the southern regions they can grow to 150-300
g (Mikheev and Mejsner 1966). Steffens (1981) states, that pikeperch
after 4 weeks of rearing in tanks and fed on sieved plankton
(0.2 mm mesh size initially; 0.3 mm mesh size for fry > 6.5
mm) are 2 cm long. Hilge (1990) observed a growth increase
from 2 g to more than 300 g in about 1 year in the laboratory
under continuous warm water conditions of 22-24°C. This
temperature is apparently below the optimum level. Commercial
trout pellets from different manufacturers were used
exclusively (4247 % raw protein, 8-14 % raw fat, 1.5-3 % raw
fibre, 9% raw ash). He could also demonstrate the striking
differences in growth depending on water temperature at the
early phase of exogenous feeding using Artemia salina nauplii
as the only food source. Growth of fry at temperatures near to
those usually found around the spawning time of 1416°C was
very poor and body weight after 2 week was only 1jS of that of
animals kept at 22°C. This corresponds to observationsreported by different authors investigating feeding and development
of pike-perch larvae in their natural en\x ' onments.
In ponds treated with organophosphate compounds, pikeperch
larvae will find zooplankton communities dominated by
rotatoria and nauplii followed by copepods later on (Verreth
and Kleyn 1987). In untreated ponds, cladocerans were dominant.
The authors observed a fast change in feed preferences
from nauplii to organisms of a larger size. There seems to be a
general scheme described by several authors in prey preference
or succession from nauplii to rotatoria, copepodites, copepods,
small cladocerans, big cladocerans to mysids and chironomids.
In 7 weeks the pike-perch larvae grew from the start of exogenous
feeding to 80 mg body weight at water temperatures
varying between 14 and 18°C. The nutrition of young pikeperch
in ponds during the first year was examined by Morduchai-
Boltovskoj (1957), Steffens (1960b) and Zhmurova
(1982). The quantity of invertebrates in ponds often decreases
in late summer (second half of August, September), which can
cause starvation of pike-perch fingerlings (Steffens et al. 1995).
Fish fry of suitable size seems to be a food necessary for rearing
large pike-perch fingerlings (Nagel 1959). In ponds of the
Kuban region (Russia) containing high quantities of small forage
fish, 1-year-old pike-perch reached a weight of 500 g (Zhukova
1960).
In recent years, different research groups have initiated feeding
experiments on pike-perch fry using live plankton or artificial
larval diets. This includes the observation of abiotic
parameters as well as the cytochemical analysis of the development
of the gut functions in relation to the transition from
endogenous to exogenous feeding. Zhmurova (1986) described
experiments on first feeding of pike-perch fry with egg yolk for
3 days and dry starter feed for the following 7 days using
an automatic feeder. Mani-Ponset et al. (1994) demonstrated
physiological abnormalities in lipid metabolism of larvae fed
on either zooplankton or on an artificial larval diet. Better
performing larval diets are therefore a prerequisite for any
successful rearing technique for pike-perch fry. In fact, there
seems to be a general lack of adequate artificial larval diets that
could be used during this early phase. Larvae fed on such
diets presented hepatic alterations as compared to those fed
on zooplankton. Klein Breteler (1989) obtained 2.5 cm fry by
feeding Artemiu and subsequently zooplankton for 5 weeks.
The survival rate was low (about 26%) due to cannibalism
during that period; 33 % of the fingerlings showed deformations.
In another experiment using three different commercially-
available manufactured diets there was no success,
due to inadequate larval feeds which resulted in poor growth
and high mortalities (Ruuhijarvi et al. 1991). The feeding of a
test diet, which had been given with good success to carp and
coregonids, revealed that although the feed was ingested there
was no digestion (Schlumberger and Proteau 1991). In another
feeding trial with a larval starter, fish exhibiting good growth
had a sudden high mortality at the time of intestinal convolution
(Proteau et al. 1993). More intensive research on the larval and
older stages of pike-perch will be necessary to overcome all the
problems related to diets. Furthcr study is necded to address
rearing conditions, including water temperature, light intensity,
feeding frequencies, and finally, body malformations, cannibalism
and multi-modality of length distribution of fingerlings.
It should be stressed that the nutritional requirements of older
stages of pike-perch still have to be determined. The physical
properties of the manufactured diets such as sinking rate, stability,
colour and shape of pellet must be studied as well. The
importance of attractants in artificial diets for this species is
apparently unknown
