FISHERY BUI l.ETIN: VOL. 72. NO. 2 



food dispensef 



recess into which a clean tank 

 bottom can be inserted 



nylon screw secumg 

 tank bottom 



removable tank 

 bottom 



nylon mesh 



10 cm 



Figure 1. — Vertical section through the larvae rearing tank. In 

 use the tank is suspended within a larger plastic vessel. 



Figure 2. — Photograph of one of the larvae rearing units in use. 



round the cylindrical tank and was firmly clipped 

 onto it by a bayonet attachment. This circular 

 piece of Durapipe was covered with 0.75 mm aper- 

 ture nylon mesh to retain larvae and possibly 

 permit uneaten food to escape. In the event the 

 food tended to swell after being in the water for 

 some time and only a portion of it passed through 



the screen at the bottom of the tank. To facilitate 

 tank cleaning and hygiene, therefore, an exactly 

 similar cover could be fitted over the top of the 

 cylindrical tank and the tank slowly and carefully 

 inverted in the outer vessel so that the bottom 

 cover was now at the top and could readily be 

 removed together with adhering uneaten food. 

 This cleaning arrangement is not ideal, but by 

 permitting the removal of much of the uneaten 

 food from the bottom of the tank, it allowed posi- 

 tive control over tank hygiene and water quality. 

 These factors have been a major obstacle to culti- 

 vation of larval fish on artificial diets in earlier 

 experiments. As the larvae grew larger it became 

 more and more possible to siphon uneaten food 

 from the bottom of the tank without endangering 

 or losing larvae. 



Food was dispensed into the tank with the in- 

 flowing water by means of an automatic feeder of 

 the type described by Adron (1972). This feeder 

 was held on a clamp stand adjacent to the tank and 

 could readily be removed when the tank was being 

 cleaned by inversion. Approximately 15 mg dry 

 food was introduced into the water via a mixing 

 chamber at 10 min intervals, the flow rate of water 

 being about 150 ml/min. The experiment was car- 

 ried out at a temperature of 10° ± 2°C with a light 

 intensity at the water surface of 250 lux provided 

 by fluorescent light. 



The composition of the food used is shown in 

 Table 1. Freeze-dried cod muscle and shrimp meal 

 were prepared as in Cowey, Pope, Adron, and 

 Blair (1972). Freeze-dried whole hen's egg was 

 prepared by drying homogenized hen's egg in a 

 bulk centrifugal freeze drier. The gelatin (pre- 



Table 1. -Composition of diet used for rearing larval plaice. 



Component 



g;100 g dry diet 



2 Water 



150 ml 



'Cowey et al. 1972 



^Removed finally by freeze drying 



354 



