Present studies focus on the microbial control of penaeid larval cultures and on the use of recirculation systems for crustacean postlarva culture.
A first set of trials (Chapter 2) evaluated the beneficial effect of a single dose of live microalgae, microalga exudates, and probiotic bacteria from microalga growth cultures on the larviculture of penaeid first feeding larval stages feeding upon artificial microdiets. Results indicate that the presence of live microalga cells improves survival, development and growth as opposed to the addition of either water where the microalga cells were filtered out or water with microalga culture enrichment nutrients. Beneficial and detrimental effects were observed as early as the first two larval development stages. A second set of trials (Chapter 3) investigated the effects of different initial water quality treatments where Microbiological composition changes were induced through mechanical, chemical and biological water treatment methods. The treatments produced significant effects on the larva capacity to survive and moult into the next larval stages as early as during first two larval stages.
In Chapter 4, the feeding appendages and digestive tract of penaeid N auplius5 and Zoea1 larval stages are described with respect to their ability to ingest and excrete bacteria. Results from histological sections, scanning electron microscopy and in vivo, in situ real time observation of live fluorescent stained bacteria suggest bacterial colonisation may start as early as Nauplius. At this stage they already have an anal pore and antiperistalsis movements occur which are capable of bringing bacteria present in the water column into the digestive tract.
The effects of two water exchange regimes were tested in the growout of two decapod crustacean postlarvae species ( Callinectes sapidus and Litopenaeus vannamei) ( Chapter 5). The pattern of ammonia and nitrite accumulation under continuous water recirculation was compared to the patterns under standard batch water exchange procedures. Both methods were tested at three different daily percentage renewal rates. Survival and growth using continuous recirculation were similar to results obtained with traditional batch water exchange.
The effect of initial stocking density of two penaeid postlarvae species (Litopenaeus vannamei and Farfantepenaeus brasiliensis) under closed recirculation conditions is evaluated in Chapter 6. Results indicate a stocking density between 200-300 early postlarvae as optimal.