Seed supply 346-9
limitations for cage culture 212
Selective feeding, for maximum growth
154-6
Semi-intensive cage culture 226-4
aquatic and terrestrial plants 220-2
defined 220
growth rates 222
with low protein mixed feeds 223-4
production 222
species used listed 222, 224
supplemental feed 220-2
Senescent period, defined 64
Septicaemias 255-6
Sertoli cells 131
Serum esterase, studied in tilapias 273-4
Serum markers, developed to identify F1
hybrids 270
Serum transferrins 271-3
Sewage, and tilapia ponds a controversial
topic 350
Sex determination, not well understood
in tilapias 280
Sex ratios, affected by mixing species 11
affected by temperature 314
best for high broodstock performance
347
best for production of fry and finger-
lings 214-5
effect of environmental factors
discussed 127
of parents and fry production 323
in various crosses 280
Sex reversal, anabolic steroids discussed
315
cost of methods discussed 315
hormone treatment discussed 316
and increased growth discussed 306-7
and monosex culture 310-2
to produce all-male populations 191
and space as a limiting factor discussed
315-6
Sexing tilapias, discussed 201-2
errors specified 201-2
manual method used in Israel 310
Sexual maturity, size at for 17 species 74-5
Sexual steroids, and control of reproduc-
tive activities 135-6
Shaba, breeding of S. macrochir 45
breeding of T. rendalli 45
introductions to artificial lakes 24
Shoaling behavior, see Schooling
Shock syndrome, in high density culture
260
Silver carp, see Hypophthalmichthys
molitrix
Sinking pelleted feeds, intensive cage
culture trials 228-9
Site, factors influencing choice for
cage culture 211
Size, influence on distribution 52
and temperature tolerances 37
Size at maturity, factors affecting 339-40
size of water body 110
water level 110
Skin damage, repair mechanism in fish
discussed 262
Slopes of rivers, and distribution of
tilapias 32
Slime bacteria, and diseases in tilapias
254-5
Snake head, see Channa striata, mudfish,
Ophicephalus striatus
Social factors, regulation of reproductive
activity 134-5
Soda Lakes, alkalinity and fish kills 109
ecological studies 100-1
Somatic growth, in relation to stunting
and gametogenesis 336-40
Soudanian species, distribution 4,17
named 17,85
Space factor, and mortalities in high
density culture 260
Spatial segregation, factors affecting 51-5
of tilapias in L. Victoria 92
Spawning, and environmental factors 337
factors affecting hybrid production
299-302
in floating cages 213
influenced by light and temperature
314
interspecific 321-5
large fish inhibit small fish? 337
mouthbrooders 47
substrate spawners 46
and temperature in pond culture 189
Spawning behavior 46-9
and incompatibility in interspecific
crosses 322-5
in L. Malawi 98
S. karomo 47
S. variabilis 47
T. rendalli 46
T. zillii 46
Spawning frequency, fecundity and
fry production discussed 328-9
evidence for flexibility 339
exchange of water beneficial 318