Topic 4B

Question 1

Finfish reproduction cycle

Answer 1

1. Spawning (eggs + sperm)
2. Embryo/fish larvae (1-15mm)
   - Absorb nutrients from attached yolk sac
3. Metamorphosis (biological change in morphology) –> after approx 10 days
4. Fish fry –> complete depletion of yolk sac; able to feed on their own
5. Juvenile (fingerling)
6. Adult –> reached maturity; able to spawn

Question 2

Ovaries

Answer 2

• Shades of light pink to dark yellow –> due to mature oocytes full of yolk granules

Question 3

Testes

Answer 3

• Whitish from beginning of maturation to the mature stage

Question 4

Molluscs

Answer 4

1. Bivalve (hinged shells)
2. Gastropod (snails/slugs)
3. Cephalopod (internal shell + tentacles)

Question 5

Mollusc reproduction

Answer 5

• Mostly external fertilisation
• Internal fertilisation in some gastropods
• Usually dioecious; some hermaphroditic

Question 6

Life cycle of bivalve/gastropod

Answer 6

1. Spawning (sperm + eggs)
2. Trochophore (aka planktonic stage)
   - Free swimming larvae
   - Bands of cilia
3. Veliger
   - Organs develop
   - Takes the morphology of a juvenile bivalve
   - suspends in water column
4. Metamorphosis (biological change in morphology –> settle down into substrate)
5. Spat/juvenile
   - settled into substrate & growing
6. Adult

Question 7

Location of gonads in mussels

Answer 7

Within mantle tissue

Question 8

Location of gonads in clams

Answer 8

At base of foot

Question 9

Location of gonads in oysters

Answer 9

Covers the outer surface of digestive gland

Question 10

Location of gonads of abalone

Answer 10

Left side of shell, under the foot

Question 11

Location of gonads of topshell

Answer 11

Near shell apex

Question 12

Type of spawning (mussels, clams, oysters, abalone, topshell)

Answer 12

Broadcast spawner

Question 13

How to identify sex of bivalve

Answer 13

• Colour of gonads (orange for females, cream for males)

- Identify male-associated polypeptide (only present in male; detection through gel electrophoresis)

Question 14

How to observe maturity of bivalve

Answer 14

• Round & fully developed eggs = ripe gonads
• Elongated eggs with no nucleus = unripe gonads
• use microscope

Question 15

Life cycle of shrimp

Answer 15

1. Fertilised eggs
2. Nauplius
3. Protozoa
4. Metamorphosis
5. Mysis
6. Megalopa
7. Juvenile

Question 16

Sex of shrimp

Answer 16

Male: Petasma (narrow structure, found b/w the foremost pair of swimming legs)
Female: Thelycum (broader structure, b/w the last pair of pleopods which provides an anchor site for male sperm packet received during copulation

Question 17

Different stages of development of shrimp

Answer 17

Stage 1 (immature): Transparent & not visible 
Stage 2 (developing): Early maturation, olive green
Stage 3 (nearly ripe): Expanded, dull-greyish green 
Stage 4 (ripe): Diamond shaped, dark olive green
Stage 5 (spent): Flaccid

Question 18

Internal fertilisation shrimp (process)

Answer 18

• Mostly occur at night & shortly after moulting of the female
• Approach –> male follows female
• Crawling –> crawl his head under female’s tail
• Chasing –> male chases escaping female
• Mating –> male turns ventral side up & grasp female/inverted
• Deposit of spermatophore onto the thelycum of female
  (Closed thelycum: ripe female, before ovarian maturatiion; Open thelycum: female w ovarian maturation, immediately before spawning)

Question 19

Life cycle of crab

Answer 19

1. Adult spawning
2. Zoea (4-5 moults)
3. Megalopa
4. Crablet/juvenile
5. Adult
   Note: the warmer the water, the faster the crab moves through the stages

Question 20

Stages of development in crab

Answer 20

Stage 1 (immature): translucent/pale-white 
Stage 2 (developing): early maturation, light yellow
Stage 3 (pre-maturing): expanded, yellow to orange
Stage 4 (ripe): occupies available space in capacity, orange to red-orange

Question 21

Mating behaviour of crabs

Answer 21

Mostly occur at night; shortly after moulting

1. Pre-copulation: matured males attracted to immature females, grab female, position her under his abdomen, male extends chelipeds out for defense
2. Molting: male guards aggressively over female
3. Copulation: flips female around, female opens up abdomen –> allow transfer of sperm