Introduction
The common European cuttlefish (Sepia officinalis) is the most used cuttlefish in research and is becoming an increasingly important aquaculture species due to its fast growth rates, adaptability to artificial food and other features (Sykes et al., 2011). Control of reproductive function in captivity is essential for the sustainability of commercial aquaculture production. It relies on species specific biological and physiological knowledge and culture conditions, which will ultimately influence animal welfare (Conte 2004). Sykes et al., (2014) recently reviewed the state of the art of S. officinalis culture and both him and Villanueva et al., (2014) have identified control over reproduction as a bottleneck in cuttlefish/cephalopods culture development.
In nature, cuttlefish are social only for reproduction, producing complex intraspecific visual displays (Hanlon et al., 1999) and form short-term female-male pair associations (Boal, 1997). Males use visual displays to probably establish size-based dominance hierarchies, where large males mate more frequently (Adamo & Hanlon, 1996; Boal, 1997). During copulation, males display sperm removal behaviour (Hanlon et al., 1999) suggesting last sperm precedence which manifests itself in mate guarding after copulation. S. officinalis is a semelparous species and this implies a different brood stock management that used for most finfish. Until now, it has been a common practice to use cultured broodstocks to obtain animals for the subsequent generations (Sykes et al., 2006). Such closed-cycle practice with captive breeders may have led to reproductive isolation from wild populations and a resultant loss of genetic variability due to the low effective breeding population size and inbreeding. We need to address this issue, by determining the effective number of breeders contributing for reproduction in an integrative way, by using behavioural analysis.
Although a number of studies to date have investigated best rearing conditions (e.g. Sykes et al, 2011) with increase in growth rates and fecundity the goal, few studies have focused solely on welfare in light of the change in legislation (but see Tonkins et al., 2015, Cooke and Tonkins, 2015). The tanks in which breeding adults are kept can have a great effect on their behaviour and ultimately welfare. Cuttlefish are epibenthic (Hanlon and Messenger, 1996) on hatching but spend at least some of their adult lives floating in the water column, possibly looking for prey and also mates. Being semelparous sexually mature individuals go through an intense breeding phase where males vigorously and aggressively compete females and females are often harassed into copulation. Given this knowledge of their life history some shapes of tanks are likely to be better than others in terms of promoting welfare. Here, we performed the first cuttlefish "big brother" and followed a large number of cuttlefish from juvenile stage right through adulthood until the onset of senescence. We believe that the different bottom areas/tank volumes will contribute differently to social behaviour within.
Materials and Methods
This study collected video samples from 3 different tank types for analysing cuttlefish reproductive behaviour. 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♂. The tanks differ in height (2 types, same volume, different surface area and height) and surface area (one tank with reduced height, same surface area as one other tank with therefore reduced volume). We will also be able to analyse how different sex ratios reduce or increase negative behaviours. Initially a sex ratio of 2:1 (f:m) was created but this shifts towards an increase in the number of males as females die earlier due to reproductive fatigue/senescence.
At the beginning of the experiments, underwater stationary micro video cameras were placed inside the tanks. These cameras supplied an analog colour video feed to digital-video recording hard-drives. All the tanks were set with 4 cameras running 24/7. To identify the time of day where reproductive and other social interactions occur more frequently, video samplings were obtained at different times (circa 1 hour after sunrise, midday and 1 hour before sunset). Recorded video feeds for each tank were processed using the computerised system for behaviour recording and analysis, "The Observer XT 9.0", as described in Barata et al., (2008). Data is being analysed 'blind' ensuring observer bias is not a factor. The constant video capture of >190 adult individuals is unique, using very detailed cuttlefish welfare based tables we will analyse videos capturing behaviours spanning 4 months which includes the transition from juvenile to full adult to reproduction and senescence. The videos will also reveal many behaviours that may have significant welfare implications but are seen at insufficient frequency during studies unable to approach ours in magnitude. For example, dominance hierarchies have only once been recorded in cuttlefish (Boal, 1997). This information is not enough, we need to learn the nature of these hierarchies (linear, despotic, etc.) to ensure they do not impact on welfare in captivity. Despotic hierarchies may mean less overall agonistic interactions after formation and encourage a sex ratio of 1: >1 (m:f) if all other males are completely excluded from reproduction. Alternatively, linear hierarchies can lead to constant severe interactions. Without the analysis of the comprehensive video resource this information will not be available.
Results
Video recordings are still being analysed and extensive and detailed preliminary analysis will be ready by September 2016.
References
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