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DEPARTMENT OF PRIMARY INDUSTRY, FISHERIES AND MINES Reproduction.

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Presentation on theme: "DEPARTMENT OF PRIMARY INDUSTRY, FISHERIES AND MINES Reproduction."— Presentation transcript:

1 DEPARTMENT OF PRIMARY INDUSTRY, FISHERIES AND MINES Reproduction

2 DEPARTMENT OF PRIMARY INDUSTRY, FISHERIES AND MINES Establish the reproductive strategy of black jewfish. Aim

3 DEPARTMENT OF PRIMARY INDUSTRY, FISHERIES AND MINES 1.Determine the spawning season and the relevance of the annual aggregations. 2.Establish the size of sexually mature black jewfish (minimum and I 50 ). 3.Document the current size/age structure of black jewfish landings. Objectives

4 DEPARTMENT OF PRIMARY INDUSTRY, FISHERIES AND MINES Over a two year period, 70 fish per month were measured, weighed and sampled. Fish sourced from commercial fishers and fishing tour operator landings. Additional fish ( 130 cm) sourced from commercial and rec. fishers. General Methods

5 DEPARTMENT OF PRIMARY INDUSTRY, FISHERIES AND MINES Reproduction Study Methods Gonad sampling: –Individual lobes weighed; section of one lobe preserved. Gonad processing: –Sectioned and stained; Classified based on oocyte stages.

6 DEPARTMENT OF PRIMARY INDUSTRY, FISHERIES AND MINES Classification System StageMost advanced oocyteOther key criteria F1ImmatureChromatin nucleolar or perinucleolar Thin gonad wall; Brown bodies not present; Compact, well packed lamellae; May have atretic cortical alveoli oocytes. F2DevelopingCortical alveoli (yolk vesicle) May have atretic oocytes; May also have post-ovulatory follicles and brown bodies. F3DevelopedYolk globuleMay have atretic oocytes; May also possess brown bodies. F4Pre-spawningMigratory nucleusOvary appears disorganised; Brown bodies may be present; May have post-ovulatory follicles if fish has spawned already. F5SpawningHydratedOvary appears disorganised; Post-ovulatory follicles, brown bodies and atretic oocytes may be present. F6SpentAtretic vitellogenicLammellae disrupted and disorganised; Vasculated in late spent stage; Brown bodies generally present. F7RestingChromatin nucleolar or perinucleolar Thick gonad wall; Brown bodies common but not always present; Lammellae not compact, often vaculated.

7 DEPARTMENT OF PRIMARY INDUSTRY, FISHERIES AND MINES Mean GSI Relative gonadosomatic index and standard deviation for females (n = 529). Spawning Season

8 DEPARTMENT OF PRIMARY INDUSTRY, FISHERIES AND MINES F2 – Developing gonads Histological Results

9 DEPARTMENT OF PRIMARY INDUSTRY, FISHERIES AND MINES F3 – Developed gonads Histological Results

10 DEPARTMENT OF PRIMARY INDUSTRY, FISHERIES AND MINES F4 & F5 – Near spawning gonads Histological Results

11 DEPARTMENT OF PRIMARY INDUSTRY, FISHERIES AND MINES Histological Results F6 – Spent gonads

12 DEPARTMENT OF PRIMARY INDUSTRY, FISHERIES AND MINES F7 – Resting gonads Histological Results

13 DEPARTMENT OF PRIMARY INDUSTRY, FISHERIES AND MINES F2 Developing (July) F3 Developed (October) F6 Spent (February) F7 Resting (May) F4-5 Near Spawning (November) Histological Results

14 DEPARTMENT OF PRIMARY INDUSTRY, FISHERIES AND MINES Spawning Size Size at first maturity Minimum size of maturity = 85 cm Maximum size of immaturity = 100 cm I 50 estimate = ~90 to 95 cm. Need to run logistic model.

15 DEPARTMENT OF PRIMARY INDUSTRY, FISHERIES AND MINES Size Structure Length/weight of black jewfish harvested near Darwin, (n = 1490). Length (cm) Weight (kg)

16 DEPARTMENT OF PRIMARY INDUSTRY, FISHERIES AND MINES Size Structure Length/weight of black jewfish harvested near Darwin, (n = 1490). Length (cm) Weight (kg) Mature Fish

17 DEPARTMENT OF PRIMARY INDUSTRY, FISHERIES AND MINES Length/weight of black jewfish harvested near Darwin, 2004 (n = 415). Length (cm) Weight (kg) Length (cm) Size Structure

18 DEPARTMENT OF PRIMARY INDUSTRY, FISHERIES AND MINES Length/weight of black jewfish harvested near Darwin, 2005 (n = 636). Length (cm) Weight (kg) Size Structure

19 DEPARTMENT OF PRIMARY INDUSTRY, FISHERIES AND MINES Length/weight of black jewfish harvested near Darwin, 2006 (n = 438). Length (cm) Weight (kg) Length (cm) Size Structure

20 DEPARTMENT OF PRIMARY INDUSTRY, FISHERIES AND MINES Summary GSI indicates extended spawning = Aug to Jan. GSI and histology suggests serial spawning. Minimum size = 85 cm; I 50 = ~90-95 cm. No apparent difference in size between years.


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