[INSIGHTS] Selecting a supplementary vegetable for target feeding of herbivorous fish in Shipwreck Habitat

INSIGHTS is our new series of posts featuring findings documented by the S.E.A. Aquarium curatorial team. These findings will go a long way to enhance our marine life and husbandry knowledge, as well as our breeding and conservation efforts.

First up, a Final Year Project by intern Lau Xin Hui who graduated in 2016 with a Diploma in Veterinary Technology from the School of Applied Science, Temasek Polytechnic. Mentored by Curator Akira Yeo and Aquarist Charles Chan, Xin Hui embarked on this interesting study on selecting a supplementary vegetable to target feed herbivorous fish in the Aquarium’s Shipwreck Habitat.

This is her project report.


Introduction

Compared to carnivorous fish, herbivorous fish aren’t able to break down food as efficiently, which may lead to dietary deficiency. They also tend to excrete more waste, leading to poor water quality and health issues such as Marine Head & Lateral Line Erosion – the development of small depressions around the eye, head and adjacent area.

Objectives

  • Adopt the best supplementary vegetable to meet the nutritional requirements via a target feeding device
  • Determine if the water quality of the tank will improve by adding the right types of vegetables into their diet

Materials and Methods

1. Five types of vegetables were selected: Chinese cabbage, lettuce, seaweed, carrot and cucumber.

2. Six large floating cages (130 x 90 x 65cm) made from PVC pipes and mesh gratings were used:

Supplementary vegetable for target feeding herbivorous fish

  • Each cage housed foxface rabbitfish with Marine Head & Lateral Line erosion.
  • 100g of a different type of vegetable was placed into each cage via a target feeding device. The cages were then placed in a corner of the tank.
  • Different target feeding devices were used to determine which was the most effective way to feed the fish.

Target feeding device 1: 30mm PVC pipes with a slit in the middle to hold the vegetables. It is then tied to the base of the cage using cable ties.
Supplementary vegetable for target feeding herbivorous fish

Target feeding device 2: 15mm wire mesh rolled into a cylindrical form. A 4-pound weight was attached to the base to let it sink to the bottom of the floating cage.
Supplementary vegetable for target feeding herbivorous fish

Target feeding device 3: an acrylic pipe with 2-inch holes were drilled through to allow access to the vegetables. Suction cups were attached to the top to prevent vegetables from floating up.
Supplementary vegetable for target feeding herbivorous fish

Observations

Most popular vegetable: seaweed

Effectiveness of target feeding device:

  • Device 1: Ineffective – no change in the weight of the vegetables. Fishes were seen hiding in the corners and most vegetables floated to the surface.
  • Device 2: Much more effective than device 1, especially for seaweed. Foxface rabbitfish were seen pecking at the vegetables.
  • Device 3: Most effective with the least vegetables floating on the surface.

Water quality: results showed that ammonia and pH levels were rather consistent and stayed within the optimal range towards the end of the experiment.

Supplementary vegetable for target feeding herbivorous fish

Improvement in Marine Head & Lateral Line erosion:
The fish  presented a slight improvement in their skin condition with fewer lesions, especially among those seen eating seaweed.

Conclusion

The addition of vegetables to their diet improved their general body condition and overall water quality of the tank. The use of target feeding device allows herbivorous fishes to not compete with one another for vegetables. Also, seaweed was the most popular vegetable due to their unique texture.

A feeding device (show below) was also constructed based on the data collected from all three target feeding devices used in the experiment. This device is built using FRP grating as the base, with artificial corals attached together to create a dome to house the vegetables. The corals were not packed tightly together to allow fishes to swim through and gain access to the vegetables.

Supplementary vegetable for target feeding herbivorous fish
This target feeding device, as well as target feeding device 3, have since been used in the aquarium to target feed our fishes more effectively.

It is recommended that the experiment be conducted using a larger group of research models over a longer period of time to allow for more accurate results. Lengthening the period of study would also allow further evaluation of the Marine Head & Lateral Line erosion condition on the fish.

 

The original report has been edited for context and clarity for the purpose of this blog.

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