THE USE OF SUB-TROPICAL EAST COAST COPEPOD

SPECIES AS LIVE FEED FOR FISH LARVICULTURE

INTRODUCTION

The sustainability of marine fin fish significantly relies on the production cost

relative to yield 1. One of the main challenges facing this industry is the

availability of a cheap nutritional food source for rearing marine larvae.

Many marine fish larvae feed on smaller zooplankton species. This is due to

poor visual accuracy and a limited gape size , which consequently relies

on the inherent movement of zooplankton for larvae to feed on2.

In marine aquaculture, Artemia and rotifers are commonly used as feed. In

comparison to rotifers and Artemia, copepods have been proven to

increase the survival and growth rate of marine larvae due to their

excellent fatty acid content and adequate docosahexaenoic acid (DHA) to

eicosapentaenoic acid (EPA) ratio1.

This study aims to: (1) compare copepod species abundance, richness and

distribution along the Mlalazi estuary and Mtunzini fish farm (Fig. 4)

located on the east coast of South Africa; and (2) identify an alternate

copepod food source for dusky kob larvae, by determining their optimum

salinity and temperature ranges (Fig. 5-7).

This experiment can be used to advance the aquaculture industry by

providing a cheap, local and nutritional source of food for marine larvae.

The results obtained can also be used by the Mtunzini fish farm to provide

an adequate food source for their dusky kob larvae.

METHODS

Study Site

Sample collection

The copepods were collected during the day and night by vertical tow using a plankton

net.

Experiment 1 (Fig. 2): Samples were fixed using 10% formalin, stained using rose

Bengal and analysed for species abundance and richness, using three 20 ml sub-

samples.

Experiment 2 (Fig. 3): Live copepod samples (species 1 & 7) in aerated honey jars

were subjected to three different temperatures and salinities to test survival, with three

replicates each3 .

Sample statistics

As data was non- parametric (p< 0.05) a Kruskal-Wallis test was used to determine

whether treatments and sites were identical, followed by a linear regression model to

compare (a) species and sites for experiment 1 and (b) the treatments for experiment 2.

All statistical analyses were conducted using Rcommander, version 3.2.2.

RESULTS

• Highest abundance occurred in site 4 (Day), and site 2 (Night). Species 1 was the most abundant during day and night (Fig. 4A & B).

CONCLUSIONS

• Species abundance decreases along the Mlalazi estuary from the head (site 4) to the mouth (site 6) which is probably due to the changes

in salinity and temperature.

• Copepods species richness in the fish farm and estuary is higher at night (6 spp.) than during the day (4 spp.).

• Highest survival of copepod Pseudodiaptomus hessei (Mrázek, 1894) occurs at high temperatures (27 °C) and low salinities (25 psu), while

that of harpacticoid species 7 occurs at low temperatures (18 °C) and high salinities (35 psu).

• We recommend than an alternate copepod food source for dusky kob larvae is Pseudodiaptomus hessei (Mrázek, 1894), due to their

shared preference for high temperatures and low salinities.

REFERENCES

[1] Kassim, Z., John, A., Chin, L. K., Zakaria, F., & Asgnari, H., 2014. Sustainable Technique for Selected Live Feed Culture. Sustainable Aquaculture Techniques, Chapter 4: 105–133.

[2] Graeb, D. S. B., & Dettmers, M. J., 2004. Fish Size and Prey AvailabilityAffect Growth , Survival , Prey Selection , and Foraging Behaviour of Larval Yellow

Perch. Transactions of the American Fisheries Society, 133: 504–514.

[3] Vengadeshperumal, N., Damotharan, P., Rajkumar, M., Perumal, P., Vijayalakshmi, S., & Balasubramanian, T., 2010. Laboratory Culture and Biochemical Characterization of the

Calanoid Copepod , Acartia southwelli Sewell, 1914 and Acartia centrura Giesbrecht, 1889. Advances in Biological Research, 4(2): 97–107.

• The highest average survival of Pseudodiaptomus hessei

(Mrázek, 1894) over a 4 day period, occurred in treatment

6 (27 °C, 20 psu) with a survival of 42 %, followed by

treatment 7 with 36 % survival (27 °C, 25 psu) (Fig 5).

• The average survival in treatments was higher than the

control (30 %) (23 °C, 28 psu). The lowest survival

however was observed in treatment 4 (27 °C, 35 psu),

with a value of 22 %.

• The highest average survival of harpacticoid (species 7)

over a 4 day period (Fig. 6), occurred in treatment 9 (20

°C, 35 psu) with a value of 74 %.

• The survival was higher than observed in the control (52

%) (20 °C, 30 psu). The lowest survival however, was

observed in treatment 5 (27 °C, 30 psu), with a value of

38 %.

• The highest average survival of harpacticoid (species 7)

over a 13 day period (Fig. 7), occurred in treatment 9 (18

°C, 35 psu) with a value of 40 %, followed by

treatments 1 (39 %) (23 °C, 25 psu).

• The survival was higher than the control (31 %) (22 °C, 31

psu).

Figure 4A & B: Average copepod abundance, richness and distribution at each site along the Mtunzini fish farm (site 1-3) and Mlalazi estuary

(site 4-6) during the day (4A) and night (4B) (+/- SE)

Figure 5: Experiment 2.1 average survival of copepod Pseudodiaptomus

hessei (Mrázek, 1894) at different temperature and salinity

treatment (T) combinations per day, with replicates (+/- SE)

Figure 6: Experiment 2.2 average survival of copepod species 7

(harpacticoid) at different temperature and salinity treatment

(T) combinations per day, with replicates (+/- SE)

Figure 7: Experiment 2.3 average survival of copepod species 7

(harpacticoid) at different temperature and salinity treatment

(T) combinations per day, with replicates (+/- SE)

Figure 8: Copepod species 1-7 observed in the study. 1) Calanoid- Pseudodiaptomus hessei (Mrázek, 1894); 2) Unknown (potential Pseudodiaptomus

hessei (Mrázek, 1894) juvenile); 3) Calanoid- Arcatia natalensis (Connell & Grindley, 1974); 4) Cyclopoid; 5) Harpacticoid; 6) Cyclopoid; 7)

Harpacticoid

Figure 1: Mlalazi estuary (28⁰55’54” S; 31⁰44’04” E) located on the east

coast of South Africa (sites 1-water inlet, 2– pond, 3-hatchery);

and the Mtunzini Fish Farm (28⁰56’09” S; 31⁰45’55” E) is located

near the estuary (sites 4– head, 5– middle, 6– mouth).

Figure 2: Copepods stained with rose bengal

Figure 3: Copepods subjected to varying salinity and temperature combinations

1

A B

ACKNOWLEDGEMENTS

We thank Niel Stallard (Mtunzini Fish Farm) for permission and assistance to

collect water samples and UKZN for funding assistance.