Griffiths Life fiislory of Thyisitcs atun 



693 



Table 1 



Doscription ofponad maturity stages of snoek (7\rs(7(>s aliin ) in Soutli African waters. Microscopic descriptions are given only for 

 leniaU's. 



Stage 



Macroscopic appearance 



Microscopic appearance 



1 Immature and Ovaries appear as clear, pinkish, or translucent orange Some ovaries in this stage consist entirely of pri- 



resting tubes. Eggs are not visible to the naked eye. Testes mary growth oocytes and others contain oocytes 



thread-like and clear, to ribbon-like and pinkish white to the early cortical alveoli stage, a atresia of 



in color. unyolked and /3 atresia of yolked oocytes are also 



observed. 



2 Active 



3 Ripe 



4 Ripe or running 



5 Spent 



Eggs discernible to the naked eye as yellow granules 

 that do not occupy all available space in ovary. There 

 is very little increase in the diameter of the ovary. 

 Testes are wider, triangular in cross-section, and 

 beige or cream in color. Sperm is present if the gonad 

 is cut and gently squeezed. 



Ovaries completely opaque and orange to yellow in 

 color They are larger in diameter and eggs occupy all 

 available space. Testes still larger in cross-section and 

 softer in te.xture. They become creamier in color due 

 to considerable quantities of sperm. 



Ovaries considerably larger in diameter, amber in 

 color with a substantial proportion of hydrated eggs. 

 Sperm is freely extruded when pressure is applied to 

 the abdomen of the whole fish. 



Ovaries are reduced in size, similar in appearance 

 to stage- 1 ovaries, and have a few yolked oocytes 

 remaining. These yolked oocytes are generally aspher- 

 ical and appear to be undergoing resorption. Testes 

 are shrivelled in appearance and mottled beige and 

 cream in color. A little viscous semen may still ooze 

 from the genital pore when pressure is applied to the 

 abdomen. 



Primary growth to early yolked oocytes evident. 

 Those at the end of the spawning season show a 

 high degree of « atresia. 



Primary growth to late yolk-stage oocytes pres- 

 ent. Atresia and postovulatory follicles evident in 

 some. 



All stages from primary growth to hydrated oo- 

 cytes present. 



Primary growth to advanced yolk-stage oocj^tes 

 present, but a much lower proportion of yolked 

 oocytes than in previous stages; major atresia of 

 yolked oocytes also present. 



%IRI, =10077?/,/^//?/,, 



where n = the total number of food categories considered 

 at a given taxonomic level. 



Numerical percentage contribution (Pillay, 1952) was 

 excluded because T. atun has a diverse diet and this 

 method would bias the results towards small crustaceans, 

 e.g. euphausiids and amphipods, which are not individu- 

 ally selected. Inshore samples for dietary analysis were 

 collected from the west coast (regions 1-3) while offshore 

 samples were collected from both the west coast (regions 

 1-3) and western Agulhas Bank (regions 4 and 5). 



Proportion of stomachs containing food and the mean 

 mass of stomach contents (including fish with empty stom- 

 achs) were used as indices of the rate of prey consumption 

 for adult (>75 cm) snoek. Sexual and spatial differences 

 were tested for statistical significance by using chi-square 

 tests (2x2 contingency tables) for frequency data (i.e. num- 



bers with and without food ), and a two-way ANOVA with 

 single observations for mean prey mass data. 



Monthly relative condition (Kn) was calculated for adult 

 snoek (>75 cm) as follows; 



'aFn 



Kn, =  



where Wy = the gonad and stomach content free weight 

 (g) of the i^^ individual in thej"" month; 

 FL, = the fork length (mm) of the ;"^ individual; 

 a (0.000018) and b (2.80) are constants from the 

 length-weight (gonad and stomach content free) 

 relationship derived from data collected during the 

 present study (all months combined); and 

 n = the number offish sampled in the/'^ month. 



Snoek accumulate fat as three longitudinal mesenteric 

 deposits along the outer walls of the stomach. Monthly 



