and development 72
discussed 82
major importance in evolution 66
and saltatory development 72, 74
and stunting 78
and sympatric speciation 73
Heterophyes heterophyes, human
parasite reported in tilapias 251
Hickling, C.F., was the first to report
all-male hybrids 279
Hierarchical arrangements, and spawn-
ing performance discussed 327
Hierarchical systems, in life histories 63-4
High salinity lakes 38
High stocking densities, inhibit repro-
duction 313
High Veldt, hard winters and T.
sparrmanii 4
High range 55
Homing 54-5
Hong Kong, introductions 28
Hormones, and sex reversal discussed 316
Hot springs, in L. Chilwa 34
and north American species 34
in L. Magadi 34
S. alcalicus gmhami 34
S. spilurus percivali 34
in R. Turkwel. 37
in Uaso Nyiro system 34
Hybrid crosses, female parent to be given
first 279,353
Hybrid vigor, discussed 306
Hybridization 279-307
all-male hybrids: S. niloticus x S.
hornorum 192
all-male offspring 56
all-male polyculture 192,194
and all-male populations 191
cold tolerance of crosses 298
effect on sex ratios 11
factors effecting 102
increased growth potential of males 290
and introductions 26,56
known between Tilapia spp. and
Sarotherodon spp. only after
artificial fertilization 12
techniques to produce all-male hybrids
at Pentecoste, Brazil 285
of T. zillii and T. rendalli 12
unfortunate consequences 56
in L. Victoria 12,56,91,102
see also Interspecific spawnings
Hybrids, all-male 310-11
cold tolerant when S. aureus a parent
303
commercial production of F1 males
270
experiments with various feedstuffs
199
growth in brackiiwater ponds 121
mass production of fry 317-29
S. mossambicus x S. hornorum:
Hickling's first experiments 279
S. mossambicus x S. niloticus: fry
production in cages 214
S. mossambicus x S. niloticus: inten.
sive cage culture with mixed
species 235-6
S. mossambicus x S. niloticus: used in
cage culture 206-7
S; nitoticus x S. aureus: F1 male
hybrid production 270
S. niloticus x S. aureus: serum
transferrim 272
S. niloticus x S. hornorum: cross
figured 308
S. niloticus x S. hornorum: pro-
duction system used in
Brazil 284
temperature tolerances of various
crosses 120
toleration of dissolved oxygen levels
122
and unusual sex ratios 269-70
usually relatively easy to produce
with tilapias 334
see also Interspecific spawnings
Hydrilla verticillata, in semi-intensive
cage culture 221-2
Hydrocynus sp., will eat tilapias 85
Hydrocynus vittatus, an important
predator on tilapias 94-6
Hydrodictyon sp., in semi-intensive
cage culture 221
Hydrogen sulphide, and massive fish
kills 40
Hypersaline habitats 38
Hypophthalmichthys molitrix, a carp
used in polyculture 190, 193-4
Hypophysectomy, effect on S. spilums
135IBP, see International Biological Pro-
gramme