EYE COLOR AS A EYE COLOR AS A PREDICTOR OF SOCIAL PREDICTOR OF SOCIAL

DOMINANCE IN NILE DOMINANCE IN NILE TILAPIA TILAPIA Oreochromis Oreochromis

niloticusniloticus

Emmanuel M. Vera Cruz, Reggie May L. Bero,Emmanuel M. Vera Cruz, Reggie May L. Bero,Remedios B. BolivarRemedios B. Bolivar

College of FisheriesCollege of FisheriesFreshwater Aquaculture CenterFreshwater Aquaculture CenterCentral Luzon State UniversityCentral Luzon State University

Russell J. BorskiRussell J. BorskiDepartment of BiologyDepartment of Biology

North Carolina State UniversityNorth Carolina State University

IntroductionHeterogeneous fish growth is a common

phenomenon in cultured fish populations

Variation in individual growth rates attributed in part to:

social interactionsformation of feeding hierarchies

Fish status in a stable dominance hierarchy classified as:dominant subordinate, or intermediate

In Nile tilapia the eye color pattern is a consequence of fish’s relative position in the social hierarchy (Volpato et al., 2003, Vera Cruz & Brown, 2007)

Can eye color pattern prior to the interaction predicts the outcome of contest for social dominance?

Experimental fishExperimental fish

Seventy five 3-wk old all-male Nile tilapia (mean wt = 0.87 g) was obtained from the Phil-Fishgen, CLSU, Science City of Muñoz Nueva Ecija

Maintained in a rectangular tank (2 x 1 x 1 m) receiving continuous flow of water for around 3 months

Fed four times a day (2 % BW)

Isolation

Weight & length of each fish were obtained

Isolation of 40 fish for 10 days

Monitoring of eye color pattern (ECP)

ECP was monitored for six daysECP was measured by quantifying the

darkened area between the iris & sclera; from zero (no darkening) to eight (total darkening)

The eye was divided into 8 equal parts using 4 imaginary diameter lines

2/8 or 2 3/8 or 3

Social interactionECP was recorded prior to the interaction

After 10 days of isolation, fish were size-matched for the later pairing with maximum size difference of 17.74% (mean = 2.32%±2.09)

Fish were individually marked by cutting the lower (with darker ECP) or upper (with paler ECP) part of the caudal fin

To prevent the effect of place familiarity, the fish in a pair were introduced at the same time in a new environment (30x15x 30 cm aquarium)

Data gathered

The period from time of the introduction up to the time of first agonistic attack

Number of pairs that interacted

Duration of social interaction

The change in ECP

Social status of each fish after the interaction

RESULTS

Duration of time before observance of first attack

This time duration corresponds to the duration of familiarization to the new environment of at least one individual in a pair

The mean was 4.97 min (±0.69) & only one pair exceeded 10 min

Fish can adapt to the new environment as early as 2.17 minutes.

Prior to interaction

Circling at each other, provoking the other fish to start the interaction

Fins of both fish were erected indicating that they are ready to fight

During the interaction

Biting directly at each others mouth

Biting at body part of the opponent

Biting at the caudal part of

the opponent

After the interaction

Subordinate retreating during attacks of dominant

Fish pair

Eye color pattern

Before the encounter

During the encounter

After the encounter

Dominant individual

 

Early part

Middlepart

Late part

 

 

1 & 13 1, 2 2, 8 8, 2 8, 8 8, 8 13  

2 & 11 2, 2 8, 8 8, 8 8, 2 1, 8 2  

3 & 5 3, 7 8, 8 2, 8 8, 2 8, 2 5  

4 & 37 1, 8 0, 0 2, 6 2, 2 8, 2 37  

6 & 15 3, 7 NI  

7 & 22 3, 8 8, 8 2, 8 8, 0 8, 0 22  

9 & 36 2, 4 0, 8 6, 8 2, 8 8, 2 36  

14 & 21 1, 4 8, 2 8, 4 8, 4 8, 4 21  

17 & 16 2, 3 2, 2 8, 8 8, 0 8, 2 16  

18 & 10 2, 7 2, 6 8, 0 8, 6 8, 6 10  

19 & 8 6, 8 8, 8 2, 8 7, 8 8, 2 8  

25 & 20* 6, 8 8, 2 8, 8 8, 8 2, 8 25  

23 & 29 7, 7.5 6, 8 4, 8 0, 8 8, 2 29  

24 & 39 6, 8 NI  

26 & 38* 3, 7 4, 8 2, 8 2, 8 2, 8 26  

27 & 31 2, 6 6, 6 8, 8 0, 2 8, 2 31  

32 & 33 4, 8 8, 8 2, 2 2, 8 8, 2 33  

34 & 30* 0, 4 8, 8 8, 2 0, 8 0, 8 34  

40 & 12 4, 8 8, 8 8, 8 8, 8 8, 2 12  

35 & 28 2, 7 8, 8 2, 8 8, 2 8, 2 28  

NI – no interaction

Social interaction

18 of the 20 pairs interacted

In this 18 pairs, 14 (77.78%) fish with darker ECP prior to pairing became dominant

Frequency difference was highly significant (Binomial test, P = 0.009)

It is important to note that during the start of the social conflict in all the 18 pairs, the opponents with paler ECP were the ones that initiated the encounter & they were the ones that first bit & chased the opponent

Duration of interaction

Group Number of pairs (n)

Mean duration of interaction

(min)

ECP difference

Short Interaction(< 5 min)

4 4.24+0.14 5.25+0.63

LongInteraction(> 5 min)

14 9.29+0.52 2.66+0.43

ANOVA P = 0.001 P = 0.008

Part of the social encounter

Pairs with the following change in ECP (%)

Pale-Paler:

Dark-Darker

Pale-Darker:

Dark-Darker

Pale-Darker:

Dark-Paler

Pale-Paler:

Dark-Paler

Early part 11 61 11 17

Middle part 33 39 22 6

Late part 28 17 55 0

After the

encounter 22 6 72 0

In dominant fish, any change in ECP after the interaction was either towards paler or darker than the original ECP while for subordinate fish it was only for darker

ConclusionsTilapia with darker ECP before the

interaction has a greater possibility to win the fight

Subordination increased the ECP patterns of the fish after pairing

In dominant fish, any change in ECP after the interaction was either towards paler or darker than the original ECP

Shorter duration of social encounter is needed for the establishment of dominance hierarchy in pairs having greater difference in ECP prior to social encounter.

Recommendations

Further investigations on the ECP of fish is needed to answer the ff. questions:

1. Is ECP of the fish consequences of prior social (dominance or subordination) experience or is it a coping style used as a flexible behavioral strategy?

2. Is the degree of change in ECP after the interaction compared to the original ECP prior to interaction caused by the level of stress (i.e aggressive encounter) received during the interaction?

3. What are the factors influencing the change in ECP in both opponents during the early stage of the conflict?

Funding for this research was provided by the

COLLABORATIVE RESEARCH SUPPORT

PROGRAM

The AquaFish CRSP is funded in part by United States Agency for International Development (USAID)

Cooperative Agreement No. EPP-A-00-06-00012-00 and by US and Host Country partners.

The contents of this presentation do not necessarily represent an official position or policy of the United States Agency for International Development

(USAID). Mention of trade names or commercial products in this presentation does not constitute endorsement or recommendation

for use on the part of USAID or the AquaFish Collaborative Research Support Program. The accuracy, reliability, and originality of the work presented are the responsibility of the individual authors.

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