Introduction
Cephalopods are gaining momentum as an alternate group for aquaculture species diversification, not only because they are a good food source (highly appreciated in some worldwide markets) but they also have the potential to quickly reach a market size. Sykes et al. (2014) recently reviewed the state of the art of Sepia officinalis culture and both him and Villanueva et al. (2014) have identified control over reproduction as a bottleneck in cuttlefish/cephalopods culture development. According to Sykes et al. (2013), the existing protocol for cuttlefish reproduction in captivity does not allow replication of results and this is probably due to not accounting for given variables, which probably have importance in increasing reproduction performance. Those are sex ratio, available space and the sexual behavior displayed when given tanks are used, which will have influence on parental contribution to offspring and population management to avoid genetic erosion and inbreeding in captive conditions. The objective of this experiment was to test the effect of tanks with different increasing volume and bottom areas on cuttlefish reproduction performance.
Material and Methods
A total of 192 juvenile cuttlefish with a mean wet weight (MWW) of 32.7±4.0g were used. These were placed in different tanks: three 3000L (3.24m2 area; B's), three 9000L (7.07m2 area; K's), and two 9000L (6.67m2 area; Q's). Each replicate/tank was set with 24 juvenile cuttlefish (which corresponded to densities of 7, 3 and 4 cuttlefish.m-2, respectively for B's, K's and Q's tanks) and a sex ratio of 2♀:1♂. All cuttlefish were weighed, every 15 days, until the start of reproduction. Data collected was used to calculate: Mean Wet Weight (MWW); Mean Absolute Instantaneous Growth Rate (MAIGR; %BW.d-1); Total Absolute Mortality (TAM); Mean Cumulative Mortality (MCM; %); Biomass (B; g); Mean Biomass Relative Increase index (B%; % BW.d-1). Additional data was collected regarding cuttlefish reproduction and used to calculate: Duration of Reproduction Stage (DRS; days); Fecundity (F; eggs); Total Egg Biomass (EB; g); Mean Individual Fecundity (IF; eggs.female-1); Mean, Maximum and Minimum egg weight (MEW; MaxIEW; MinIEWg); Mean female and male weight (MW♀; MW♂; g); Dorsal mantle length (DML); Eviscerated, gonads and digestive gland wet weight; Gonadossomatic Index (GI); Digestive Gland Index (DGI); Number of Egg Batches (Ba; n); Number of Eggs per Batch (EBa; eggs.batch-1); Viable and non-viable eggs; Egg viability (%); and Mean Hatchling Weight (MHW; g). Sex ratios were verified at the end of the experiment. Viable and non-viable eggs were sorted by external morphology and colour, according to table 11.2 and fig. 11.3 of Sykes et al. (2014). Egg Viability of was determined randomly in 100 viable eggs from a tank batch placed 2.6L hatching tanks (22.0cmx14.5cmx8.0cm) of a semi-open seawater system (250L). This procedure was performed three times in each tank, depending on egg availability for each tank.
Results and Discussion
Cuttlefish displayed a life span of 289 days, which was much larger than that recorded previously by Sykes et al. (2006), in consecutive generations, and Sykes et al. (2013). The main differences found at the end of the growth stage was as higher mortality in the B tanks.
Despite one the of B tanks contributed with only 369 eggs, the 8 tanks generated a total of 123751 eggs (in 85 postures), which is not only the highest number of eggs ever obtained at CCMar's facilities but also a number of eggs that may meet the requirements of a small scale cuttlefish commercial hatchery facility. This is even more significant if we consider that these results were obtained with an F5 generation of captive cuttlefish breeders and that the experimental tanks were placed outside the premises.
There were two K tanks reaching a production of approximately 24000 eggs/tank and individual fecundities of 1500 eggs/female. It is interesting that both K and Q tanks presented not only high values of total fecundity but also that these were fairly consistent between replicates, when compared with B tanks. In the present experiment, a lower number of batches but a higher number of eggs per batch was verified, being these much more consistent in K tanks. The non-viable egg percentage increased, when compared with the Sykes et al. (2013) paper, but this was probably due to the use of a F5 generation, while the previous used a F1.
