5.2 FEEDING AND NUTRITION

5.2.1 Introduction

Feeding commences as soon as larvae become fully shelled and their organs including the digestive system have developed.

Prior to that time, energy for respiration and development is derived from reserves laid down during egg development (oogenesis) by the maturing females (see 5.3.4). It is also likely that developing embryos are able to absorb organic nutrients from the surrounding seawater. Indeed, there is often benefit in adding a little cultured algal food to tanks containing embryos 12 hours before they have reached the D-larva stage and are capable of ingesting particulate food. It may not be the algal cells themselves that are important but rather organic nutrients in solution in the algal cultures. In this respect, the addition of small quantities of diatoms (e.g. Chaetoceros muelleri at 10 to 20 cells per ?l) from cultures nearing the stationary phase appears to be most effective.

Once the velum is developed at the D-larva stage and the fully shelled larvae are swimming, the beat of the velar cilia direct food particles towards the mouth as well as providing the motive force for swimming activity (Figure 67). At this point – Day 0 as it is usually referred to – the quality (diet composition) and quantity (ration) of food added to culture tanks becomes important.

Figure 67: Larvae feed as they swim. Beating of the cilia of the swimming organ, the velum, also directs food particles towards the mouth. The three Day 8 scallop larvae shown are swimming on a collision course.
Their darkly coloured digestive glands are clearly visible.